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  • 1. Alcamán, M. Estrella
    et al.
    Alcorta, Jaime
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Vásquez, Mónica
    Polz, Martin
    Díez, Beatriz
    Physiological and gene expression responses to nitrogen regimes and temperatures in Mastigocladus sp strain CHP1, a predominant thermotolerant cyanobacterium of hot springs2017In: Systematic and Applied Microbiology, ISSN 0723-2020, E-ISSN 1618-0984, Vol. 40, no 2, p. 102-113Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria are widely distributed primary producers with significant implications for the global biogeochemical cycles of carbon and nitrogen. Diazotrophic cyanobacteria of subsection V (Order Stigonematales) are particularly ubiquitous in photoautotrophic microbial mats of hot springs. The Stigonematal cyanobacterium strain CHPI isolated from the Porcelana hot spring (Chile) was one of the major contributors of the new nitrogen through nitrogen fixation. Further morphological and genetic characterization verified that the strain CHP1 belongs to Stigonematales, and it formed a separate Glade together with other thermophiles of the genera Fischerella and Mastigocladus. Strain CHP1 fixed maximum N-2 in the light, independent of the temperature range. At 50 degrees C niJH gene transcripts showed high expression during the light period, whereas the nifH gene expression at 45 degrees C was arrhythmic. The strain displayed a high affinity for nitrate and a low tolerance for high ammonium concentrations, whereas the narB and glnA genes showed higher expression in light and at the beginning of the dark phase. It is proposed that Mastigocladus sp. strain CHPI would represent a good model for the study of subsection V thermophilic cyanobacteria, and for understanding the adaptations of these photoautotrophic organisms inhabiting microbial mats in hot springs globally.

  • 2. Allen, Lisa Zeigler
    et al.
    McCrow, John P.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Dupont, Christopher L.
    Badger, Jonathan H.
    Hoffman, Jeffery M.
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Allen, Andrew E.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Venter, J. Craig
    The Baltic Sea Virome: Diversity and Transcriptional Activity of DNA and RNA Viruses2017In: mSystems, ISSN 2379-5077, Vol. 2, no 1, article id UNSP e00125-16Article in journal (Refereed)
    Abstract [en]

    Metagenomic and metatranscriptomic data were generated from size-fractionated samples from 11 sites within the Baltic Sea and adjacent marine waters of Kattegat and freshwater Lake Tornetrask in order to investigate the diversity, distribution, and transcriptional activity of virioplankton. Such a transect, spanning a salinity gradient from freshwater to the open sea, facilitated a broad genome-enabled investigation of natural as well as impacted aspects of Baltic Sea viral communities. Taxonomic signatures representative of phages within the widely distributed order Caudovirales were identified with enrichments in lesser-known families such as Podoviridae and Siphoviridae. The distribution of phage reported to infect diverse and ubiquitous heterotrophic bacteria (SAR11 clades) and cyanobacteria (Synechococcus sp.) displayed population-level shifts in diversity. Samples from higher-salinity conditions (>14 practical salinity units [PSU]) had increased abundances of viruses for picoeukaryotes, i.e., Ostreococcus. These data, combined with host diversity estimates, suggest viral modulation of diversity on the whole-community scale, as well as in specific prokaryotic and eukaryotic lineages. RNA libraries revealed single-stranded DNA (ssDNA) and RNA viral populations throughout the Baltic Sea, with ssDNA phage highly represented in Lake Tornetrask. Further, our data suggest relatively high transcriptional activity of fish viruses within diverse families known to have broad host ranges, such as Nodoviridae (RNA), Iridoviridae (DNA), and predicted zoonotic viruses that can cause ecological and economic damage as well as impact human health. IMPORTANCE Inferred virus-host relationships, community structures of ubiquitous ecologically relevant groups, and identification of transcriptionally active populations have been achieved with our Baltic Sea study. Further, these data, highlighting the transcriptional activity of viruses, represent one of the more powerful uses of omics concerning ecosystem health. The use of omics-related data to assess ecosystem health holds great promise for rapid and relatively inexpensive determination of perturbations and risk, explicitly with regard to viral assemblages, as no single marker gene is suitable for widespread taxonomic coverage.

  • 3.
    Bauer, Karolina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Lugomela, Charles
    Seppälä, Susanna
    Borg, Agneta Julia
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Variability in benthic diazotrophy and cyanobacterial diversity in a tropical intertidal lagoon.2008In: FEMS Microbiol Ecol, ISSN 0168-6496, Vol. 63, no 2, p. 205-21Article in journal (Refereed)
  • 4.
    Berg, Carlo
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Dupont, Chris L.
    Asplund-Samuelsson, Johannes
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Celepli, Narin A.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Eiler, Alexander
    Allen, Andrew E.
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Ininbergs, Karolina
    Dissection of Microbial Community Functions during a Cyanobacterial Bloom in the Baltic Sea via Metatranscriptomics2018In: Frontiers in Marine Science, E-ISSN 2296-7745, article id UNSP 55Article in journal (Refereed)
    Abstract [en]

    Marine and brackish surface waters are highly dynamic habitats that undergo repeated seasonal variations in microbial community composition and function throughout time. While succession of the various microbial groups has been well investigated, little is known about the underlying gene-expression of the microbial community. We investigated microbial interactions via metatranscriptomics over a spring to fall seasonal cycle in the brackish Baltic Sea surface waters, a temperate brackish water ecosystem periodically promoting massive cyanobacterial blooms, which have implications for primary production, nutrient cycling, and expansion of hypoxic zones. Network analysis of the gene expression of all microbes from 0.22 to 200 mu m in size and of the major taxonomic groups dissected the seasonal cycle into four components that comprised genes peaking during different periods of the bloom. Photoautotrophic nitrogen-fixing Cyanobacteria displayed the highest connectivity among the microbes, in contrast to chemoautotrophic ammonia-oxidizing Thaumarchaeota, while heterotrophs dominated connectivity among pre- and post-bloom peaking genes. The network was also composed of distinct functional connectivities, with an early season balance between carbon metabolism and ATP synthesis shifting to a dominance of ATP synthesis during the bloom, while carbon degradation, specifically through the glyoxylate shunt, characterized the post-bloom period, driven by Alphaproteobacteria as well as by Gammaproteobacteria of the SAR86 and SAR92 clusters. Our study stresses the exceptionally strong biotic driving force executed by cyanobacterial blooms on associated microbial communities in the Baltic Sea and highlights the impact cyanobacterial blooms have on functional microbial community composition.

  • 5.
    Bergman, Birgitta
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ran, Liang
    Stockholm University, Faculty of Science, Department of Botany.
    Adams, David G
    Cyanobacterial-plant symbiosis: signaling and development2008In: The Cyanobacteria: Molecular Biology, Genomics and evolution, Caister Academic Press, Norfolk, UK , 2008, p. 447-473Chapter in book (Other academic)
  • 6.
    Bergman, Birgitta
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Rasmussen, Ulla
    Stockholm University, Faculty of Science, Department of Botany.
    Rai, Amar N
    Cyanobacterial Associations2007In: Associative and Endophytic Nitrogen-fixing Bacteria and Cyanobacterial Associations., Kluwer Academic Publishers, Dordrecht , 2007, p. 257-301Chapter in book (Other academic)
  • 7.
    Bergman, Birgitta
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Sandh, Gustaf
    Stockholm University, Faculty of Science, Department of Botany.
    Lin, Senjie
    Larsson, John
    Stockholm University, Faculty of Science, Department of Botany.
    Carpenter, Edward J.
    Trichodesmium - a widespread marine cyanobacterium with unusual nitrogen fixation properties2013In: FEMS Microbiology Reviews, ISSN 0168-6445, E-ISSN 1574-6976, Vol. 37, no 3, p. 286-302Article, review/survey (Refereed)
    Abstract [en]

    The last several decades have witnessed dramatic advances in unfolding the diversity and commonality of oceanic diazotrophs and their N2-fixing potential. More recently, substantial progress in diazotrophic cell biology has provided a wealth of information on processes and mechanisms involved. The substantial contribution by the diazotrophic cyanobacterial genus Trichodesmium to the nitrogen influx of the global marine ecosystem is by now undisputable and of paramount ecological importance, while the underlying cellular and molecular regulatory physiology has only recently started to unfold. Here, we explore and summarize current knowledge, related to the optimization of its diazotrophic capacity, from genomics to ecophysiological processes, via, for example, cellular differentiation (diazocytes) and temporal regulations, and suggest cellular research avenues that now ought to be explored.

  • 8.
    Bergman, Birgitta
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Zheng, Weiwen
    Ekman, Martin
    Ran, Liang
    Stockholm University, Faculty of Science, Department of Botany.
    The cyanobacterium–Azolla symbiosis: Interactions and cell differentiation2007In: Abstracts of the Annual Main Meeting of the Society for Experimental Biology, Glasgow, Scotland, 31st March - 4th April, 2007, 2007Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Selected cyanobacteria form stable nitrogen-fixing symbioses with diverse eukaryotes. The water-fern Azolla carries a nitrogen-fixing cyanobacterium (cyanobiont) in its leaves and shows a pronounced intimacy between its partners. It is the only perpetual N2-fixing symbiosis, i.e. the cyanobiont is vertically transmitted in sporocarps between plant generations. The cyanobiont also seems incapable of independent growth which may suggest gene loss and that the symbiosis is on its way to evolve into a N2-fixing plant. Proteomic analyses of the cyanobiont (2-D coupled to MS) resulted in an identification of about 79% of proteins analysed. Processes upregulated were related to energy production, nitrogen and carbon metabolism and stress, while photosynthesis and metabolic turnover rates were downregulated, stressing a slow heterotrophic mode of growth, high heterocyst frequencies and nitrogen-fixing capacities. Peptide mass spectra of NifH demonstrated the presence of a 300–400 Da protein modification localized to a 13 amino acid sequence. Additionally, a short phylogenetic distance between the cyanobiont and some sequenced cyanobacteria (Section IV) and the database hits of the proteins identified by proteomics, together suggest that the Azolla cyanobiont may represent a novel cyanobacterial genus. The genome of the cyanobiont will be sequenced in 2007 (DOE/JGI, USA).

  • 9.
    Bergman, Birgitta
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Zheng, Wei-Wen
    Klint, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Ran, Liang
    Stockholm University, Faculty of Science, Department of Botany.
    On the origin of plants and relations to contemporary cyanobacterial-plant symbioses.2008In: Plant Biotechnology, Vol. 25, no 3, p. 213-220Article, review/survey (Other (popular science, discussion, etc.))
  • 10.
    Berntzon, Lotta
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of bicarbonate on LC-MS/MS analysis of BMAA using AQC or EZ: FaastTM pre-column derivatizationManuscript (preprint) (Other academic)
  • 11.
    Berntzon, Lotta
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Erasmie, Sven
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Celepli, Narin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Rasmussen, Ulla
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    BMAA Inhibits Nitrogen Fixation in the Cyanobacterium Nostoc sp PCC 71202013In: Marine Drugs, ISSN 1660-3397, E-ISSN 1660-3397, Vol. 11, no 8, p. 3091-3108Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria produce a range of secondary metabolites, one being the neurotoxic non-protein amino acid beta-N-methylamino-L-alanine (BMAA), proposed to be a causative agent of human neurodegeneration. As for most cyanotoxins, the function of BMAA in cyanobacteria is unknown. Here, we examined the effects of BMAA on the physiology of the filamentous nitrogen-fixing cyanobacterium Nostoc sp. PCC 7120. Our data show that exogenously applied BMAA rapidly inhibits nitrogenase activity (acetylene reduction assay), even at micromolar concentrations, and that the inhibition was considerably more severe than that induced by combined nitrogen sources and most other amino acids. BMAA also caused growth arrest and massive cellular glycogen accumulation, as observed by electron microscopy. With nitrogen fixation being a process highly sensitive to oxygen species we propose that the BMAA effects found here may be related to the production of reactive oxygen species, as reported for other organisms.

  • 12.
    Berntzon, Lotta
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ronnevi, L. O.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Eriksson, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    DETECTION OF BMAA IN THE HUMAN CENTRAL NERVOUS SYSTEM2015In: Neuroscience, ISSN 0306-4522, E-ISSN 1873-7544, Vol. 292, p. 137-147Article in journal (Refereed)
    Abstract [en]

    Amyotrophic lateral sclerosis (ALS) is an extremely devastating neurodegenerative disease with an obscure etiology. The amino acid beta-N-methyl-L-alanine (BMAA) produced by globally widespread phytoplankton has been implicated in the etiology of human motor neuron diseases. BMAA was recently proven to be present in Baltic Sea food webs, ranging from plankton to larger Baltic Sea organisms, some serving as important food items (fish) for humans. To test whether exposure to BMAA in a Baltic Sea setting is reflected in humans, blood and cerebrospinal fluid (CSF) from individuals suffering from ALS were analyzed, together with sex- and age-matched individuals not inflicted with ALS. Ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and multiple reaction monitoring (MRM), in conjunction with diagnostic transitions revealed BMAA in three (12%) of the totally 25 Swedish individuals tested, with no preference for those suffering from ALS. The three BMAA-positive samples were all retrieved from the CSF, while BMAA was not detected in the blood. The data show that BMAA, potentially originating from Baltic Sea phytoplankton, may reach the human central nervous system, but does not lend support to the notion that BMAA is resident specifically in ALS-patients. However, while dietary exposure to BMAA may be intermittent and, if so, difficult to detect, our data provide the first demonstration of BMAA in the central nervous system of human individuals ante mortem quantified with UHPLC-MS/MS, and therefore calls for extended research efforts.

  • 13.
    Brindefalk, Björn
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Dupont, Christopher L.
    Yooseph, Shibu
    Pinhassi, Jarone
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Distribution and expression of microbial rhodopsins in the Baltic Sea and adjacent waters2016In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 18, no 12, p. 4442-4455Article in journal (Refereed)
    Abstract [en]

    Rhodopsins are light-driven ion-pumping membrane proteins found in many organisms and are proposed to be of global importance for oceanic microbial energy generation. Several studies have focused on marine environments, with less exploration of rhodopsins in brackish waters. We investigated microbial rhodopsins in the Baltic Sea using size-fractionated metagenomic and metatranscriptomic datasets collected along a salinity gradient spanning from similar to 0 to 35 PSU. The normalised genomic abundance of rhodopsins in Bacteria, as well as rhodopsin gene expression, was highest in the smallest size fraction (0.1-0.8 mu m), relative to the medium (0.8-3.0 mu m) and large (> 3.0 mu m) size fractions. The abundance of rhodopsins in the two smaller size fractions displayed a positive correlation with salinity. Proteobacteria and Bacteroidetes rhodopsins were the most abundant while Actinobacteria rhodopsins, or actinorhodopsins, were common at lower salinities. Phylogenetic analysis indicated that rhodopsins have adapted independently to the marine-brackish transition on multiple occasions, giving rise to green light-adapted variants from ancestral blue light-adapted ones. A notable diversity of viral-like rhodopsins was also detected in the dataset and potentially linked with eukaryotic phytoplankton blooms. Finally, a new clade of likely proton-pumping rhodopsin with non-canonical amino acids in the spectral tuning and proton accepting site was identified.

  • 14.
    Celepli, Narin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Sundh, John
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dupont, Chris L.
    Yooseph, Shibu
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Meta-omic analyses of Baltic Sea cyanobacteria: diversity, community structure and salt acclimation2017In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 19, no 2, p. 673-686Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria are important phytoplankton in the Baltic Sea, an estuarine-like environment with pronounced north to south gradients in salinity and nutrient concentrations. Here, we present a metagenomic and -transcriptomic survey, with subsequent analyses targeting the genetic identity, phylogenetic diversity, and spatial distribution of Baltic Sea cyanobacteria. The cyanobacterial community constituted close to 12% of the microbial population sampled during a pre-bloom period (June-July 2009). The community was dominated by unicellular picocyanobacteria, specifically a few highly abundant taxa (Synechococcus and Cyanobium) with a long tail of low abundance representatives, and local peaks of bloom-forming heterocystous taxa. Cyanobacteria in the Baltic Sea differed genetically from those in adjacent limnic and marine waters as well as from cultivated and sequenced picocyanobacterial strains. Diversity peaked at brackish salinities 3.5-16psu, with low N:P ratios. A shift in community composition from brackish to marine strains was accompanied by a change in the repertoire and expression of genes involved in salt acclimation. Overall, the pre-bloom cyanobacterial population was more genetically diverse, widespread and abundant than previously documented, with unicellular picocyanobacteria being the most abundant clade along the entire Baltic Sea salinity gradient.

  • 15. Degerholm, Jenny
    et al.
    Gundersen, Kjell
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Söderbäck, Erik
    Seasonal significance of N2 fixation in coastal and offshore waters of the northwestern Baltic Sea2008In: Marine Ecology Progress Series, ISSN 0171-8630, Vol. 360, p. 73-84Article in journal (Refereed)
    Abstract [en]

    Annual rates of N2 fixation were measured over 3 yr (1998–2000) at an open water station (BY31) and 2 coastal stations (H4 and X1) in the Baltic Sea. This is the first report on depth-integrated rates of N2 fixation from more than one complete growth season in the Baltic Sea. Annual estimates of N2 fixation ranged from 56000 to 125000 t N in the Baltic Proper, and 18000 to 162000 t N at the inshore stations (Himmerfjärden). Rates of N2 fixation were measured in situ at 4 depths between 0 and 25 m using the 15N tracer technique for size fractionated organisms larger and smaller than 20 µm. Maximum rates of N2 fixation were found in surface waters (0 to 4 m depth), and a major part of this activity (80% in coastal and 89% in offshore waters) took place during daylight hours. Integrated rates of N2 fixation in cells >20 µm followed the average abundance of filamentous cyanobacteria (primarily Aphanizomenon sp.) in the water column. Molar C:N mass ratios in particles >20 µm, i.e. filamentous cyanobacteria, suggest that this size fraction was N-sufficient during summer, whereas the molar C:P mass ratios indicated P-limitation during this period. A reduction in sewage discharge to the Himmerfjärden bay area during the study period appears not to have been compensated for by increased rates of N2 fixation. The patchy distribution of cyanobacteria and the high seasonal variability in N2 fixation rates emphasize the need for adequate spatial and temporal sampling strategies in studies of N2 fixation in coastal and open waters of the Baltic Sea.

  • 16. DeLuca, Thomas H.
    et al.
    Zackrisson, Olle
    Bergman, Ingela
    Díez, Beatriz
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Diazotrophy in Alluvial Meadows of Subarctic River Systems2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 11, article id e77342Article in journal (Refereed)
    Abstract [en]

    There is currently limited understanding of the contribution of biological N-2 fixation (diazotrophy) to the N budget of large river systems. This natural source of N in boreal river systems may partially explain the sustained productivity of river floodplains in Northern Europe where winter fodder was harvested for centuries without fertilizer amendments. In much of the world, anthropogenic pollution and river regulation have nearly eliminated opportunities to study natural processes that shaped early nutrient dynamics of large river systems; however, pristine conditions in northern Fennoscandia allow for the retrospective evaluation of key biochemical processes of historical significance. We investigated biological N-2 fixation (diazotrophy) as a potential source of nitrogen fertility at 71 independent floodplain sites along 10 rivers and conducted seasonal and intensive analyses at a subset of these sites. Biological N-2 fixation occurred in all floodplains, averaged 24.5 kg N ha(-1) yr(-1) and was down regulated from over 60 kg N ha(-1) yr(-1) to 0 kg N ha(-1) yr(-1) by river N pollution. A diversity of N-2-fixing cyanobacteria was found to colonize surface detritus in the floodplains. The data provide evidence for N-2 fixation to be a fundamental source of new N that may have sustained fertility at alluvial sites along subarctic rivers. Such data may have implications for the interpretation of ancient agricultural development and the design of contemporary low-input agroecosystems.

  • 17. Diez, Beatriz
    et al.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Marine diazotrophic cyanobacteria: out of the blue.2008In: Plant Biotechnology, ISSN 1342-4580, Vol. 25, no 3, p. 221-225Article, review/survey (Other (popular science, discussion, etc.))
  • 18.
    Diez, Beatriz
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Pedros-Alio, Carlos
    Anto, Meritxell
    Snoeijs, Pauline
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    High cyanobacterial nifh gene diversity in arctic seawater and sea ice brine2012In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 4, no 3, p. 360-366Article in journal (Refereed)
    Abstract [en]

    Although cyanobacterial diazotrophs are common in Arctic terrestrial and freshwater habitats, they have been assumed to be absent from Arctic marine habitats. We report here a high diversity of cyanobacterial nifH genes in Fram Strait and the Greenland Sea. The nifH gene encodes the iron protein of the nitrogenase enzyme complex, which is essential for biological N2 fixation. Using primers specific for nifH genes we uncovered communities of autotrophic and heterotrophic bacteria in sea ice brine and seawater between latitudes 65 and 81 degrees N. Cyanobacteria (Oscillatoriales and Chroococcales) with known marine planktonic and benthic distributions were distinguished, alongside a mix of metabolically versatile eubacteria (nifH Clusters I and III). Using primers selective for cyanobacterial nifH genes we identified filamentous non-heterocystous Trichodesmium-like and LPP (Leptolyngbya, Phormidium and Plectonema)-like Oscillatoriales, as well as Cyanothece-like Chroococcales in a brine sample from 81 degrees N. The occurrence of Trichodesmium-like cyanobacteria was further confirmed by sequences of the hetR gene of Trichodesmium. Microscopic examinations confirmed the presence of viable filamentous and unicellular cyanobacteria. Our results reveal the potential for microbial N2 fixation in the Arctic seas. However, it is still left to determine if these genes are also metabolically active before any biogeochemical importance of diazotrophy in the polar oceans can be assessed.

  • 19. Dominguez-Escobar, Julia
    et al.
    Beltran, Yislem
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Diez, Beatriz
    Stockholm University, Faculty of Science, Department of Botany.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Botany.
    Souza, Valeria
    Falcon, Luisa I.
    Phylogenetic and molecular clock inferences of cyanobacterial strains within Rivulariaceae from distant environments2011In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 316, no 2, p. 90-99Article in journal (Refereed)
    Abstract [en]

    Heterocyst-forming cyanobacteria are important players at both evolutionary and ecological scales, but to date it has been difficult to establish their phylogenetic affiliations. We present data from a phylogenetic and molecular clock analysis of heterocystous cyanobacteria within the family Rivulariaceae, including the genera Calothrix, Rivularia, Gloeotrichia and Tolypothrix. The strains were isolated from distant geographic regions including fresh and brackish water bodies, microbial mats from beach rock, microbialites, pebble beaches, plus PCC strains 7103 and 7504. Phylogenetic inferences (distance, likelihood and Bayesian) suggested the monophyly of genera Calothrix and Rivularia. Molecular clock estimates indicate that Calothrix and Rivularia originated similar to 1500 million years ago (MYA) ago and species date back to 400-300 MYA while Tolypothrix and Gloeotrichia are younger genera (600-400 MYA).

  • 20. Dupont, Chris L.
    et al.
    Larsson, John
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Yooseph, Shibu
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Goll, Johannes
    Asplund-Samuelsson, Johannes
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    McCrow, John P.
    Celepli, Narin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Allen, Lisa Zeigler
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lucas, Andrew J.
    Hagström, Åke
    Thiagarajan, Mathangi
    Brindefalk, Björn
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Richter, Alexander R.
    Andersson, Anders F.
    Tenney, Aaron
    Lundin, Daniel
    Tovchigrechko, Andrey
    Nylander, Johan A. A.
    Brami, Daniel
    Badger, Jonathan H.
    Allen, Andrew E.
    Rusch, Douglas B.
    Hoffman, Jeff
    Norrby, Erling
    Friedman, Robert
    Pinhassi, Jarone
    Venter, J. Craig
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Functional Tradeoffs Underpin Salinity-Driven Divergence in Microbial Community Composition2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 2, p. e89549-Article in journal (Refereed)
    Abstract [en]

    Bacterial community composition and functional potential change subtly across gradients in the surface ocean. In contrast, while there are significant phylogenetic divergences between communities from freshwater and marine habitats, the underlying mechanisms to this phylogenetic structuring yet remain unknown. We hypothesized that the functional potential of natural bacterial communities is linked to this striking divide between microbiomes. To test this hypothesis, metagenomic sequencing of microbial communities along a 1,800 km transect in the Baltic Sea area, encompassing a continuous natural salinity gradient from limnic to fully marine conditions, was explored. Multivariate statistical analyses showed that salinity is the main determinant of dramatic changes in microbial community composition, but also of large scale changes in core metabolic functions of bacteria. Strikingly, genetically and metabolically different pathways for key metabolic processes, such as respiration, biosynthesis of quinones and isoprenoids, glycolysis and osmolyte transport, were differentially abundant at high and low salinities. These shifts in functional capacities were observed at multiple taxonomic levels and within dominant bacterial phyla, while bacteria, such as SAR11, were able to adapt to the entire salinity gradient. We propose that the large differences in central metabolism required at high and low salinities dictate the striking divide between freshwater and marine microbiomes, and that the ability to inhabit different salinity regimes evolved early during bacterial phylogenetic differentiation. These findings significantly advance our understanding of microbial distributions and stress the need to incorporate salinity in future climate change models that predict increased levels of precipitation and a reduction in salinity.

  • 21.
    Díez, Beatriz
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Bauer, Karolina
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Epilithic cyanobacterial communities of a marine tropical beach rock (Heron Island, Great Barrier Reef): diversity and diazotrophy.2007In: Appl Environ Microbiol, ISSN 0099-2240, Vol. 73, no 11, p. 3656-68Article in journal (Refereed)
  • 22.
    Díez, Beatriz
    et al.
    Stockholm University, Science for Life Laboratory (SciLifeLab). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Pontificia Universidad Católica de Chile, Chile; Center for Climate Change and Resilience Research (CR)2, Chile.
    Nylander, Johan A. A.
    Stockholm University, Science for Life Laboratory (SciLifeLab). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Swedish Museum of Natural History, Sweden.
    Ininbergs, Karolina
    Stockholm University, Science for Life Laboratory (SciLifeLab). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dupont, Christopher L.
    Allen, Andrew E.
    Yooseph, Shibu
    Rusch, Douglas B.
    Bergman, Birgitta
    Stockholm University, Science for Life Laboratory (SciLifeLab). Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Metagenomic Analysis of the Indian Ocean Picocyanobacterial Community: Structure, Potential Function and Evolution2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 5, article id e0155757Article in journal (Refereed)
    Abstract [en]

    Unicellular cyanobacteria are ubiquitous photoautotrophic microbes that contribute substantially to global primary production. Picocyanobacteria such as Synechococcus and Prochlorococcus depend on chlorophyll a-binding protein complexes to capture light energy. In addition, Synechococcus has accessory pigments organized into phycobilisomes, and Prochlorococcus contains chlorophyll b. Across a surface water transect spanning the sparsely studied tropical Indian Ocean, we examined Synechococcus and Prochlorococcus occurrence, taxonomy and habitat preference in an evolutionary context. Shotgun sequencing of size fractionated microbial communities from 0.1 mu m to 20 mu m and subsequent phylogenetic analysis indicated that cyanobacteria account for up to 15% of annotated reads, with the genera Prochlorococcus and Synechococcus comprising 90% of the cyanobacterial reads, even in the largest size fraction (3.0-20 mm). Phylogenetic analyses of cyanobacterial lightharvesting genes (chl-binding pcb/isiA, allophycocyanin (apcAB), phycocyanin (cpcAB) and phycoerythin (cpeAB)) mostly identified picocyanobacteria clades comprised of overlapping sequences obtained from Indian Ocean, Atlantic and/or Pacific Oceans samples. Habitat reconstructions coupled with phylogenetic analysis of the Indian Ocean samples suggested that large Synechococcus-like ancestors in coastal waters expanded their ecological niche towards open oligotrophic waters in the Indian Ocean through lineage diversification and associated streamlining of genomes (e.g. loss of phycobilisomes and acquisition of Chl b); resulting in contemporary small celled Prochlorococcus. Comparative metagenomic analysis with picocyanobacteria populations in other oceans suggests that this evolutionary scenario may be globally important.

  • 23. Ekman, Martin
    et al.
    Tollbäck, Petter
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Proteomic analysis of the cyanobacterium of the Azolla symbiosis: identity, adaptation, and NifH modification.2008In: J Exp Bot, ISSN 1460-2431, Vol. 59, no 5, p. 1023-34Article in journal (Refereed)
  • 24.
    Ekman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Tollbäck, Petter
    Department of Analytical Chemistry.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Proteomic analysis of the cyanobacterium of the Azolla symbiosis: identity, adaptation, and NifH modification.2007In: J Exp Bot, ISSN 0022-0957Article in journal (Refereed)
  • 25.
    Ekman, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Tollbäck, Petter
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Klint, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Protein expression profiles in an endosymbiotic cyanobacterium revealed by a proteomic approach2006In: Molecular Plant-Microbe Interactions, ISSN 0894-0282, E-ISSN 1943-7706, Vol. 19, no 11, p. 1251-1261Article in journal (Refereed)
    Abstract [en]

    Molecular mechanisms behind adaptations in the cyano-bacterium (Nostoc sp.) to a life in endosymbiosis with plants are still not clarified, nor are the interactions between the partners. To get further insights, the proteome of a Nostoc strain, freshly isolated from the symbiotic gland tissue of the angiosperm Gunnera manicata Linden, was analyzed and compared with the proteome of the same strain when free-living. Extracted proteins were separated by two-dimensional gel electrophoresis and were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry combined with tandem mass spectrometry. Even when the higher percentage of differentiated cells (heterocysts) in symbiosis was compensated for, the majority of the proteins detected in the symbiotic cyanobacteria were present in the free-living counterpart, indicating that most cellular processes were common for both stages. However, differential expression profiling revealed a significant number of proteins to be down-regulated or missing in the symbiotic stage, while others were more abundant or only expressed in symbiosis. The differential protein expression was primarily connected to i) cell envelope-associated processes, including proteins involved in exopolysaccharide synthesis and surface and membrane associated proteins, ii) to changes in growth and metabolic activities (C and N), including upregulation of nitrogenase and proteins involved in the oxidative pentose phosphate pathway and downregu-lation of Calvin cycle enzymes, and iii) to the dark, micro-aerobic conditions offered inside the Gunnera gland cells, including changes in relative phycobiliprotein concentrations. This is the first comprehensive analysis of proteins in the symbiotic state.

  • 26. Estrella Alcamán, María
    et al.
    Fernandez, Camila
    Delgado, Antonio
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Diez, Beatriz
    The cyanobacterium Mastigocladus fulfills the nitrogen demand of a terrestrial hot spring microbial mat2015In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 9, no 10, p. 2290-2303Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria from Subsection V (Stigonematales) are important components of microbial mats in non-acidic terrestrial hot springs. Despite their diazotrophic nature (N-2 fixers), their impact on the nitrogen cycle in such extreme ecosystems remains unknown. Here, we surveyed the identity and activity of diazotrophic cyanobacteria in the neutral hot spring of Porcelana (Northern Patagonia, Chile) during 2009 and 2011-2013. We used 16S rRNA and the nifH gene to analyze the distribution and diversity of diazotrophic cyanobacteria. Our results demonstrate the dominance of the heterocystous genus Mastigocladus (Stigonematales) along the entire temperature gradient of the hot spring (69-38 degrees C). In situ nitrogenase activity (acetylene reduction), nitrogen fixation rates (cellular uptake of N-15(2)) and nifH transcription levels in the microbial mats showed that nitrogen fixation and nifH mRNA expression were light-dependent. Nitrogen fixation activities were detected at temperatures ranging from 58 degrees C to 46 degrees C, with maximum daily rates of 600 nmol C2H4 cm(-2) per day and 94.1 nmol N cm(-2) per day. These activity patterns strongly suggest a heterocystous cyanobacterial origin and reveal a correlation between nitrogenase activity and nifH gene expression during diurnal cycles in thermal microbial mats. N and C fixation in the mats contributed similar to 3 g Nm(-2) per year and 27 g Cm-2 per year, suggesting that these vital demands are fully met by the diazotrophic and photoautotrophic capacities of the cyanobacteria in the Porcelana hot spring.

  • 27. Falcon, Luisa I
    et al.
    Lindwall, Susanne
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Bauer, Karolina
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Carpenter, Edward C
    Ultrastructure of unicellular N-2 fixing cyanobacteria from the tropical North Atlantic and subtropical North Pacific Oceans2004In: Journal of Phycology, Vol. 40, no 6, p. 1074-1078Article in journal (Refereed)
    Abstract [en]

    Abstract: Nitrogen fixing unicellular marine cyanobacteria may have a major role in the global biogeochemistry of N; nevertheless, little is known about their phylogeny and morphology. We isolated N-2 fixing unicellular cyanobacteria from the tropical North Atlantic and subtropical North Pacific Oceans and examined ultrastructural dynamics during dark:light cycles when grown in incubators. The isolate from the subtropical North Pacific was larger and showed a size variation from 3 to 7 mum but had similar morphology and cell division-plane characteristics as the isolate from the North Atlantic (2.5 mum). Nitrogen fixation only occurred during the dark phase, and ultrastructural analysis demonstrated changes in the appearance and quantity of large carbohydrate-like granules present in the cells. To verify the composition of these carbohydrate-like granules, staining with periodic acid, thioacetic acid, and silver was carried out, and a positive reaction was obvious in all cells. The cells from the Atlantic seemed to empty their polysaccharide granules during the night, whereas those from the Pacific showed a decrease in the number of their granules. Our work suggests that phylogenetically related strains of unicellular N-2 fixing cyanobacteria from different oceans showed similar carbohydrate-like granules that could be used to fuel N-2 fixation during darkness.

  • 28. Hamisi, M. I.
    et al.
    Lugomela, C.
    Lyimo, T. J.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Díez, Beatriz
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Pontificia Universidad Católica de Chile, Chile; Center for Climate Change and Resilience Research, Chile.
    Plankton composition, biomass, phylogeny and toxin genes in Lake Big Momela, Tanzania2017In: African Journal of Aquatic Science, ISSN 1608-5914, E-ISSN 1727-9364, Vol. 42, no 2, p. 109-121Article in journal (Refereed)
    Abstract [en]

    Lake Big Momela, one of the East African soda lakes in Northern Tanzania characterised by highly saline-alkaline conditions, making them inhospitable to a range of organisms, although supporting massive growths of some adapted planktonic microorganisms that serve as food for birds, such as Lesser Flamingo. The temporal dynamics of plankton, with an emphasis on cyanobacteria, were examined in 2007 using morphological traits and ribosomal genetic markers (16S and 18S rRNA). Cyanobacterial genes encoding for hepatotoxins (mcyE and ndaF) were also screened. Rotifers and copepods dominated the zooplankton, whereas cyanobacteria, such as Anabaenopsis elenkinii and Arthrospira fusiformis dominated the phytoplankton community, and these being related to representatives in other East African soda lakes. The cyanobacteria community also showed distinct seasonal patterns influenced by environmental parameters, mainly salinity, pH and nitrate. Significant positive correlations were found between phytoplankton abundance and nitrate concentrations (r = 0.617, p = 0.033). No signals of the hepatotoxin synthetase genes mcyE and ndaF were retrieved from cyanobacteria during the whole year. In general, our data illustrate the presence of rich planktonic communities, including some unique and potentially endemic cyanobacteria.

  • 29. Hamisi, Mariam
    et al.
    Diez, Beatriz
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Thomas
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Epiphytic cyanobacteria of the seagrass Cymodocea rotundata: diversity, diel nifH expression and nitrogenase activity2013In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 5, no 3, p. 367-376Article in journal (Refereed)
    Abstract [en]

    Seagrasses are photoautotrophic, ecologically important components of many globally widespread coastal ecosystems, in which combined nitrogen may limit their production. We examined the biodiversity and diazotrophic capacity of microbial epiphytes associated with the phyllosphere of the seagrass Cymodocea rotundata of the Western Indian Ocean. Light microscopy, 16S rRNA and nifH gene analysis revealed the dominance of cyanobacteria in the epiphytic microbial community. Most phylotypes were related to free-living uncultured benthic cyanobacteria, while some to cyanobacterial endosymbionts of marine diatoms. Novel and potentially diazotrophic species, some of known pantropical distribution, were also discovered. Significant diel nitrogenase activities (acetylene reduction assay) were recorded (up to 358 +/- 232nmolC2H4g1 of seagrass FWh1). The nifH gene expression patterns showed that heterocystous phylotypes may be the dominant diazotrophs during the day and non-heterocystous at night. These data show that C.rotundata is colonized by diverse diazotrophic cyanobacteria species and suggest that these may be beneficial partners of seagrasses in nitrogen-depleted waters.

  • 30.
    Hamisi, Mariam
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Institut de Ciéncies del Mar (ICM), CMIMA-CSIC, Barcelona.
    Lyimo, Thomas
    University of Dar es Salaam, Tanzania.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Cyanobacteria associated with the phyllosphere of the seagrass Cymodocea rotundata: Diversity, diel nifH expression and nitrogenase activity: Diversity, nifH expression and activity in seagrassManuscript (preprint) (Other academic)
    Abstract [en]

    Tropical seagrass ecosystems are highly productive and extremely important for sustaining marine life. As seagrasses are associated with complex assemblages of poorly examined epiphytic microbes, we proposed that nitrogen-fixing microorganisms may contribute to the productivity. The morphological and genetic diversity (based on the 16S rRNA and nifH genes) of cyanobacteria and diel variations in nifH gene expression, NifH protein levels and nitrogenase (nitrogen-fixing) activity were examined in the phyllosphere of Cymodocea rotundata of coastal areas of the western Indian Ocean (Tanzania). The 16S rRNA and nifH gene analyses during two consecutive years (October-November, 2007 and 2008) revealed the dominance of a mixed cyanobacterial community. Most sequences represented free-living uncultured cyanobacteria previously reported as benthic in the region, clearly separated from marine planktonic phylotypes, while a few sequences clustered with cyanobacterial symbionts of diatoms. Appreciable, but varying nitrogenase activities were found on a diel as well as monthly basis, with the highest activity encountered, 358 ± 232 and 258 ± 139 nmol C2H4 g-1 h-1, in November. On a diel basis, nifH gene expression coincided with the NifH protein level (Oct 2008) and nitrogenase activity. At day time, nifH gene expression primarily originated from heterocystous phylotypes, while from non-heterocystous filamentous phylotypes (mainly Oscillatoriales) at night. The data suggest that a variety of diazotrophic cyanobacteria are common among the epiphytes on Cymodocea and we propose that these may represent a valuable source of ‘new’ nitrogen in the often oligotrophic, but ecologically important seagrass ecosystems.

  • 31.
    Hamisi, Mariam I.
    et al.
    University of Dodoma, School of Natural Sciences and Mathematics.
    Mvungi, Esther F.
    Stockholm University, Faculty of Science, Department of Botany.
    Lyimo, Thomas J.
    University of Dar es Salaam, Department of Molecular Biology and Biotechnology.
    Mamboya, Florence A.
    Dar es Salaam Institute of Technology, Department of Sciences and Laboratory Technology.
    Österlund, Katrin
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Institut de Ciéncies del Mar (ICM), CMIMA-CSIC, Barcelona.
    Nutrient enrichment affects the seagrass Cymodocea serrulata and induces changes to its epiphytic cyanobacterial communityManuscript (preprint) (Other academic)
    Abstract [en]

    To better understand how elevated water column nutrient levels affect the performance of the seagrass Cymodocea serrulata as well as the composition and density of its associated epiphytes, two sets of experiments were carried out where nutrient concentration were manipulated in a flow though system containing seagrasses. The photosynthetic performance, growth characteristics and nutrient content (N:P) were followed for C. serrulata. Simultaneously the biomass, species composition for the epiphytic cyanobacteria, in particular diazotrophs was monitored. The photosynthetic capacity of seagrasses decreased with increase in nutrient concentrations and exposure time. Nutrient contents of seagrass leaves and epiphytes decreased after nutrient addition. A higher diversity of both heterocystous and non-heterocystous cyanobacteria was observed in the experimental seagrasses as compared with natural field samples. Many of the cyanobacterial sequences retrieved represented uncultured and potentially novel diazotrophic phylotypes. Diel nitrogenase activity measurements verified the presence of a distinct proportion of diazotrophs, which was negatively affected by moderate nutrient levels. These results demonstrate that seagrasses were physiologically stressed by the increased nutrient level as revealed by low maximum quantum yields, although the effect was not instant. In contrast the epiphytes whose response was apparent during the short term exposure to moderate nutrient concentration which also promoted rapid change in their composition.

  • 32.
    Hamisi, Mariam
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Lyimo, Thomas
    University of Dar es Salaam, Tanzania.
    Muruke, Masoud
    University of Dar es Salaam, Tanzania.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Nitrogen fixation by epiphytic and epibenthic diazotrophs associated with seagrass meadows along the Tanzanian coast, Western Indian Ocean2009In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 57, p. 33-42Article in journal (Refereed)
    Abstract [en]

    Seasonal, diurnal, and age-dependent variations in nitrogen fixation (nitrogenase activity) by epiphytic diazotrophs colonizing the seagrasses Halodule uninervis, Cymodocea rotundata, Thalassodendron ciliatum, and Thalassia hemprichii, and by epibenthic diazotrophs associated with seagrass-vegetated and nonvegetated sediments, were estimated at 2 sites along the Tanzanian coast, Western Indian Ocean. Acetylene reduction-gas chromatography showed that nitrogenase activity values were significantly higher (p = 0.0004) at the site with low nutrient levels (Mjimwema) than at the site with higher nutrient levels (Ocean Road). The nitrogenase activity ranged from 10 to 192 nmol N g–1 h–1 for H. uninervis, 7 to 80 nmol N g–1 h–1 for C. rotundata, 10 to 75 nmol N g–1 h–1 for Thalassia hemprichii, and from 4 to 61 nmol N g–1 h–1 for Thalassodendron ciliatum. Nitrogenase activity values in sediments covered by seagrasses were significantly higher than in surrounding nonvegetated sediments (t = 4.021, p = 0.0005). Significant variations in nitrogenase activity were apparent depending on leaf age and season, with highest activity being found in mid-aged leaves during the northeastern monsoon (NEM), and in older leaves during the southeastern monsoon (SEM). Daytime nitrogenase activity was appreciable on above-ground seagrass parts, while rhizosphere activity peaked at night-time. Collectively our data show that diazotrophs (cyanobacteria and other bacteria) are associated with seagrasses (leaves and roots), and potentially constitute an integral part of the ecosystem. They show highly dynamic nitrogenase activity and a succession in seagrass colonization, and we concluded that their presence may contribute to the productivity of the seagrass beds.

  • 33.
    Ininbergs, Karolina
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Larsson, John
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab). Linnaeus University, Sweden.
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Stockholm University, Science for Life Laboratory (SciLifeLab).
    Microbial metagenomics in the Baltic Sea: Recent advancements and prospects for environmental monitoring2015In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 44, p. 439-450Article in journal (Refereed)
    Abstract [en]

    Metagenomics refers to the analysis of DNA from a whole community. Metagenomic sequencing of environmental DNA has greatly improved our knowledge of the identity and function of microorganisms in aquatic, terrestrial, and human biomes. Although open oceans have been the primary focus of studies on aquatic microbes, coastal and brackish ecosystems are now being surveyed. Here, we review so far published studies on microbes in the Baltic Sea, one of the world's largest brackish water bodies, using high throughput sequencing of environmental DNA and RNA. Collectively the data illustrate that Baltic Sea microbes are unique and highly diverse, and well adapted to this brackish-water ecosystem, findings that represent a novel base-line knowledge necessary for monitoring purposes and a sustainable management. More specifically, the data relate to environmental drivers for microbial community composition and function, assessments of the microbial biodiversity, adaptations and role of microbes in the nitrogen cycle, and microbial genome assembly from metagenomic sequences. With these discoveries as background, prospects of using metagenomics for Baltic Sea environmental monitoring are discussed.

  • 34.
    Jonasson, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Eriksson, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Berntzon, Lotta
    Stockholm University, Faculty of Science, Department of Botany.
    Rasmussen, Ulla
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    A novel cyanobacterial toxin (BMAA) with potential neurodegenerative effects2008In: Plant Biotechnology, ISSN 1342-4580, E-ISSN 1347-6114, Vol. 25, no 3, p. 227-232Article in journal (Refereed)
    Abstract [en]

    The non-protein amino acid beta-N-methyl-amino-L-alanine (BMAA) is a neurotoxin that was recently found to be produced by most cyanobacteria. The neurotoxin was discovered in 1967 in the seeds of the cycad Cycas micronesica, but this BMAA may originate from the symbiotic cyanobacterium Nostoc, which inhabits the roots of cycads. BMAA is thought to be the cause of the deadly neurodegenerative disease amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC), common among the Chamorro people of Guam. It was demonstrated that the Chamorros, in all probability, have been exposed to high levels of BMAA through dietary consumption of flying foxes which fed mainly on cycads seeds. BMAA production may be a common conserved evolutionary feature among cyanobacteria and due to their wide global distribution, the toxin may be a common concern and potentially involved in provoking degenerative diseases worldwide. BMAA may likewise be bioaccumulated in other cyanobacterial based food webs within ecosystems outside Guam, and it is proposed that such webs may exist in the Baltic Sea, with its massive occurrence of cyanobacteria (blooms).

  • 35.
    Jonasson, Sara
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Eriksson, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Berntzon, Lotta
    Stockholm University, Faculty of Science, Department of Botany.
    Spacil, Zdenek
    Stockholm University, Faculty of Science, Department of Analytical Chemistry. Charles University Prague, Czech Republic .
    Ilag, Leopold L.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Ronnevi, Lars-Olof
    Rasmussen, Ulla
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Transfer of a cyanobacterial neurotoxin within a temperate aquatic ecosystem suggests pathways for human exposure2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 20, p. 9252-9257Article in journal (Refereed)
    Abstract [en]

    beta-methylamino-L-alanine (BMAA), a neurotoxic nonprotein amino acid produced by most cyanobacteria, has been proposed to be the causative agent of devastating neurodegenerative diseases on the island of Guam in the Pacific Ocean. Because cyanobacteria are widespread globally, we hypothesized that BMAA might occur and bioaccumulate in other ecosystems. Here we demonstrate, based on a recently developed extraction and HPLC-MS/MS method and long-term monitoring of BMAA in cyanobacterial populations of a temperate aquatic ecosystem (Baltic Sea, 2007-2008), that BMAA is biosynthesized by cyanobacterial genera dominating the massive surface blooms of this water body. BMAA also was found at higher concentrations in organisms of higher trophic levels that directly or indirectly feed on cyanobacteria, such as zooplankton and various vertebrates (fish) and invertebrates (mussels, oysters). Pelagic and benthic fish species used for human consumption were included. The highest BMAA levels were detected in the muscle and brain of bottom-dwelling fishes. The discovery of regular biosynthesis of the neurotoxin BMAA in a large temperate aquatic ecosystem combined with its possible transfer and bioaccumulation within major food webs, some ending in human consumption, is alarming and requires attention.

  • 36.
    Klint, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ran, Liang
    Stockholm University, Faculty of Science, Department of Botany.
    Rasmussen, Ulla
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Identification of developmentally regulated proteins in cyanobacterial hormogonia using a proteomic approach.2006In: Symbiosis, ISSN 0334-5114, Vol. 41, no 2, p. 87-95Article in journal (Refereed)
  • 37.
    Klint, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Rasmussen, Ulla
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    FtsZ may have dual roles in the filamentous cyanobacterium Nostoc/Anabaena sp. strain PCC 7120.2007In: J Plant Physiol, ISSN 0176-1617, Vol. 164, no 1, p. 11-8Article in journal (Refereed)
  • 38.
    Larsson, John
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Celepli, Narin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dupont, Christopher L.
    Yooseph, Shibu
    Bergman, Bigitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Picocyanobacteria containing a novel pigment gene cluster dominate the brackish water Baltic Sea2014In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 8, no 9, p. 1892-1903Article in journal (Refereed)
    Abstract [en]

    Photoautotrophic picocyanobacteria harvest light via phycobilisomes (PBS) consisting of the pigments phycocyanin (PC) and phycoerythrin (PE), encoded by genes in conserved gene clusters. The presence and arrangement of these gene clusters give picocyanobacteria characteristic light absorption properties and allow the colonization of specific ecological niches. To date, a full understanding of the evolution and distribution of the PBS gene cluster in picocyanobacteria has been hampered by the scarcity of genome sequences from fresh-and brackish water-adapted strains. To remediate this, we analysed genomes assembled from metagenomic samples collected along a natural salinity gradient, and over the course of a growth season, in the Baltic Sea. We found that while PBS gene clusters in picocyanobacteria sampled in marine habitats were highly similar to known references, brackish-adapted genotypes harboured a novel type not seen in previously sequenced genomes. Phylogenetic analyses showed that the novel gene cluster belonged to a clade of uncultivated picocyanobacteria that dominate the brackish Baltic Sea throughout the summer season, but are uncommon in other examined aquatic ecosystems. Further, our data suggest that the PE genes were lost in the ancestor of PC-containing coastal picocyanobacteria and that multiple horizontal gene transfer events have re-introduced PE genes into brackish-adapted strains, including the novel clade discovered here.

  • 39.
    Larsson, John
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Nylander, Johan A. A.
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Genome fluctuations in cyanobacteria reflect evolutionary, developmental and adaptive traits2011In: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148, Vol. 11, p. 187-Article in journal (Refereed)
    Abstract [en]

    Background: Cyanobacteria belong to an ancient group of photosynthetic prokaryotes with pronounced variations in their cellular differentiation strategies, physiological capacities and choice of habitat. Sequencing efforts have shown that genomes within this phylum are equally diverse in terms of size and protein-coding capacity. To increase our understanding of genomic changes in the lineage, the genomes of 58 contemporary cyanobacteria were analysed for shared and unique orthologs. Results: A total of 404 protein families, present in all cyanobacterial genomes, were identified. Two of these are unique to the phylum, corresponding to an AbrB family transcriptional regulator and a gene that escapes functional annotation although its genomic neighbourhood is conserved among the organisms examined. The evolution of cyanobacterial genome sizes involves a mix of gains and losses in the clade encompassing complex cyanobacteria, while a single event of reduction is evident in a clade dominated by unicellular cyanobacteria. Genome sizes and gene family copy numbers evolve at a higher rate in the former clade, and multi-copy genes were predominant in large genomes. Orthologs unique to cyanobacteria exhibiting specific characteristics, such as filament formation, heterocyst differentiation, diazotrophy and symbiotic competence, were also identified. An ancestral character reconstruction suggests that the most recent common ancestor of cyanobacteria had a genome size of approx. 4.5 Mbp and 1678 to 3291 protein-coding genes, 4%-6% of which are unique to cyanobacteria today. Conclusions: The different rates of genome-size evolution and multi-copy gene abundance suggest two routes of genome development in the history of cyanobacteria. The expansion strategy is driven by gene-family enlargment and generates a broad adaptive potential; while the genome streamlining strategy imposes adaptations to highly specific niches, also reflected in their different functional capacities. A few genomes display extreme proliferation of non-coding nucleotides which is likely to be the result of initial expansion of genomes/gene copy number to gain adaptive potential, followed by a shift to a life-style in a highly specific niche (e. g. symbiosis). This transition results in redundancy of genes and gene families, leading to an increase in junk DNA and eventually to gene loss. A few orthologs can be correlated with specific phenotypes in cyanobacteria, such as filament formation and symbiotic competence; these constitute exciting exploratory targets.

  • 40.
    Larsson, John
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Nylander, Johan
    Natural History Museum, University of Oslo.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Genome fluctuations in cyanobacteria reflect evolutionary, developmental and adaptive traitsIn: BMC Evolutionary Biology, ISSN 1471-2148, E-ISSN 1471-2148Article in journal (Refereed)
  • 41.
    Larsson, John
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Nylander, Johan
    Natural History Museum, University of Oslo.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Horizontally transferred genes in a cyanobacterial plant symbiont suggest roles in symbiosis maintenanceManuscript (preprint) (Other academic)
  • 42.
    Lin, Senjie
    et al.
    Department of Marine Sciences, University of Connecticut, USA.
    Sandh, Gustaf
    Stockholm University, Faculty of Science, Department of Botany.
    Zhang, Huan
    Department of Marine Sciences, University of Connecticut, USA.
    Cheng, Jiujun
    Stockholm University, Faculty of Science, Department of Botany.
    Perkins, Keri
    Department of Marine Sciences, University of Connecticut, USA.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Carpenter, Edward
    Romberg Tiburon Center, San Francisco State University, USA.
    Two flavodoxin genes in Trichodesmium (Oscillatoriales, Cyanophyceae): Remarkable sequence divergence and possible functional diversification2009In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 371, no 1, p. 93-101Article in journal (Refereed)
    Abstract [en]

    We analyzed flavodoxin gene sequences and transcription patterns in the marine nitrogen-fixing cyanobacterium Trichodesmium Ehrenberg ex Gomont 1892. While a typical cyanobacterial flavodoxin ortholog (fld1) was identified from cultured (strain IMS101) and environmental Trichodesmium by PCR and Southern blot hybridization, a second flavodoxin (fld2) was identified in the genome sequence. BLAST and phylogenetic analyses indicated that the two fld genes were highly divergent: fld1 was most closely related to fld common in cyanobacteria, wheras fld2 formed a distinct cluster with a fld so far only found in the unicellular diazotrophic cyanobacteria Cyanothece and Crocosphaera (in which fld2 was the only fld). The fld2 cluster was more closely allied with a fld in non-cyanobacterial diazotrophs such as Azotobacter and Azoarcus than fld1 in other cyanobacteria. This result suggests different evolutionary history of these two genes. Real-Time RT–PCR analysis on iron-replete and iron-deplete Trichodesmium cultures revealed remarkable diel dynamics in transcription of both flds but surprisingly failed to show induction under iron stress. Addition of nitrate to these cultures depressed nifH and fld2 transcription while elevating the transcription of fld1 in iron-stressed cultures. A positive correlation between fld and nifH transcript abundances was found, which was stronger in the case of fld2 than fld1. Our data suggest that these two flavodoxins in Trichodesmium may be functionally diversified and that use of flavodoxin as an iron stress indicator needs to be validated for each organism with consideration of diel dynamics of gene expression.

  • 43.
    Lundgren, Pernilla
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Bauer, Karolina
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Lugomela, Charles
    Söderbäck, Erik
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany. Växtfysiologi.
    Reevaluation of the nitrogen fixation behavior in the marine non-heterocystous cyanobacterium Lyngbya majuscula2003In: Journal of Phycology, Vol. 39, no 2, p. 310-314Article in journal (Refereed)
    Abstract [en]

    Abstract: Lyngbya majuscula Harvey ex Gomont is a common marine cyanobacterium in tropical and subtropical near-shore waters. A few reports have indicated that L. majuscula fixes nitrogen only in the light. Because this feature is uncommon among non-heterocystous cyanobacteria, we attempted a reevaluation. Nitrogenase activity, regulation, and localization were examined over diel cycles on natural populations of L. majuscula growing in subtidal zones off Zanzibar in the western Indian Ocean. The data show that L. majuscula fixed nitrogen and synthesized nitrogenase in all cells during the dark phase of a diel cycle. During the light phase, nitrogenase was degraded to undetectable levels.

  • 44. Osborne, Bruce
    et al.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Why Does Gunnera Do It and Other Angiosperms Don’t?2009In: Prokaryotic Symbionts in Plants / [ed] Katharina Pawlowski, Heidelberg, Germany: Springer Verlag , 2009, p. 207-224Chapter in book (Other (popular science, discussion, etc.))
  • 45. Plominsky, Alvaro M.
    et al.
    Delherbe, Nathalie
    Mandakovic, Dinka
    Riquelme, Brenda
    Gonzalez, Karen
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mariscal, Vicente
    Vasquez, Monica
    Intercellular transfer along the trichomes of the invasive terminal heterocyst forming cyanobacterium Cylindrospermopsis raciborskii CS-5052015In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 362, no 5Article in journal (Refereed)
    Abstract [en]

    Cylindrospermopsis raciborskii CS-505 is an invasive freshwater filamentous cyanobacterium that when grown diazotrophically may develop trichomes of up to 100 vegetative cells while differentiating only two end heterocysts, the sole sites for their N-2-fixation process. We examined the diazotrophic growth and intercellular transfer mechanisms in C. raciborskii CS-505. Subjecting cultures to a combined-nitrogen-free medium to elicit N-2 fixation, the trichome length remained unaffected while growth rates decreased. The structures and proteins for intercellular communication showed that while a continuous periplasmic space was apparent along the trichomes, the putative septal junction sepJ gene is divided into two open reading frames and lacks several transmembrane domains unlike the situation in Anabaena, differentiating a 5-fold higher frequency of heterocysts. FRAP analyses also showed that the dyes calcein and 5-CFDA were taken up by heterocysts and vegetative cells, and that the transfer from heterocysts and 'terminal' vegetative cells showed considerably higher transfer rates than that from vegetative cells located in the middle of the trichomes. The data suggest that C. raciborskii CS-505 compensates its low-frequency heterocyst phenotype by a highly efficient transfer of the fixed nitrogen towards cells in distal parts of the trichomes (growing rapidly) while cells in central parts suffers (slow growth).

  • 46. Plominsky, Álvaro M.
    et al.
    Larsson, John
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Delherbe, Nathalie
    Osses, Igor
    Vásquez, Mónica
    Dinitrogen Fixation Is Restricted to the Terminal Heterocysts in the Invasive Cyanobacterium Cylindrospermopsis raciborskii CS-5052013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 2, article id e51682Article in journal (Refereed)
    Abstract [en]

    The toxin producing nitrogen-fixing heterocystous freshwater cyanobacterium Cylindrospermopsis raciborskii recently radiated from its endemic tropical environment into sub-tropical and temperate regions, a radiation likely to be favored by its ability to fix dinitrogen (diazotrophy). Although most heterocystous cyanobacteria differentiate regularly spaced intercalary heterocysts along their trichomes when combined nitrogen sources are depleted, C. raciborskii differentiates only two terminal heterocysts (one at each trichome end) that can reach >100 vegetative cells each. Here we investigated whether these terminal heterocysts are the exclusive sites for dinitrogen fixation in C. raciborskii. The highest nitrogenase activity and NifH biosynthesis (western-blot) were restricted to the light phase of a 12/12 light/dark cycle. Separation of heterocysts and vegetative cells (sonication and two-phase aqueous polymer partitioning) demonstrated that the terminal heterocysts are the sole sites for nifH expression (RT-PCR) and NifH biosynthesis. The latter finding was verified by the exclusive localization of nitrogenase in the terminal heterocysts of intact trichomes (immunogold-transmission electron microscopy and in situ immunofluorescence-light microscopy). These results suggest that the terminal heterocysts provide the combined nitrogen required by the often long trichomes (>100 vegetative cells). Our data also suggests that the terminal-heterocyst phenotype in C. raciborskii may be explained by the lack of a patL ortholog. These data help identify mechanisms by which C. raciborskii and other terminal heterocyst-forming cyanobacteria successfully inhabit environments depleted in combined nitrogen.

  • 47.
    Ploug, Helle
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Musat, Niculina
    Adam, Birgit
    Moraru, Christina L.
    Lavik, Gaute
    Vagner, Tomas
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Kuypers, Marcel M. M.
    Carbon and nitrogen fluxes associated with the cyanobacterium Aphanizomenon sp. in the Baltic Sea2010In: The ISME journal, ISSN 1751-7362, Vol. 4, no 9, p. 1215-1223Article in journal (Refereed)
    Abstract [en]

    Carbon and nitrogen fluxes in Aphanizomenon sp. colonies in the Baltic Sea were measured using a combination of microsensors, stable isotopes, mass spectrometry, and nanoscale secondary ion mass spectrometry (nanoSIMS). Cell numbers varied between 956 and 33 000 in colonies ranging in volume between 1.4 x 10(-4) and 230 x 10(-4) mm(-3). The high cell content and their productivity resulted in steep O-2 gradients at the colony-water interface as measured with an O-2 microsensor. Colonies were highly autotrophic communities with few heterotrophic bacteria attached to the filaments. Volumetric gross photosynthesis in colonies was 78 nmol O-2 mm(-3) h(-1). Net photosynthesis was 64 nmol O-2 mm(-3) h(-1), and dark respiration was on average 15 nmol O-2 mm(-3) h(-1) or 16% of gross photosynthesis. These volumetric photosynthesis rates belong to the highest measured in aquatic systems. The average cell-specific net carbon-fixation rate was 38 and 40 fmol C cell(-1) h(-1) measured by microsensors and by using stable isotopes in combination with mass spectrometry and nanoSIMS, respectively. In light, the net C:N fixation ratio of individual cells was 7.3 +/- 3.4. Transfer of fixed N-2 from heterocysts to vegetative cells was fast, but up to 35% of the gross N-2 fixation in light was released as ammonium into the surrounding water. Calculations based on a daily cycle showed a net C: N fixation ratio of 5.3. Only 16% of the bulk N-2 fixation in dark was detected in Aphanizomenon sp. Hence, other organisms appeared to dominate N-2 fixation and NH4+ release during darkness.

  • 48.
    Ran, Liang
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Huang, Fang
    Ekman, Martin
    Stockholm University, Faculty of Science, Department of Botany.
    Klint, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Proteomic analyses of the photoauto- and diazotrophically grown cyanobacterium Nostoc sp. PCC 731022007In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 153, p. 608-618Article in journal (Refereed)
    Abstract [en]

    The filamentous cyanobacteria of the genus Nostoc are globally distributed, phenotypically complex organisms, capable of cellular differentiation and of forming symbiotic associations with a wide range of plants. To further our understanding of these processes and functions, the proteome of photoautotrophically and diazotrophically grown Nostoc sp. PCC 73102 (N. punctiforme) cells was examined. Extracted proteins were separated into membrane and soluble protein fractions and analysed using two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The analysis led to the identification of 82 proteins that could be divided into 12 functional categories. Significantly, 65 of these proteins have not been previously documented in the Nostoc proteome. Many of the proteins identified were readily recognized as housekeeping proteins involved in carbon, nitrogen and energy metabolism, but a number of proteins related to stress, motility, secretion and post-translational modifications were also identified. Ten unclassified proteins were also detected, representing potential novel functions. These proteins were highly expressed, suggesting that they play key roles during photoautotrophic and diazotrophic growth. Nineteen of the proteins expressed under the growth conditions examined contained putative thioredoxin (Trx) targets, a motif that functions in redox regulation via redox equivalent mediators and is known to be significant in a wide range of biological processes. These observations contribute to our understanding of the complex Nostoc life cycle.

  • 49.
    Ran, Liang
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Larsson, John
    Stockholm University, Faculty of Science, Department of Botany.
    Vigil-Stenman, Theoden
    Stockholm University, Faculty of Science, Department of Botany.
    Nylander, Johan A. A.
    Stockholm University, Faculty of Science, Department of Botany.
    Ininbergs, Karolina
    Stockholm University, Faculty of Science, Department of Botany.
    Zheng, Wei-Wen
    Lapidus, Alla
    Lowry, Stephen
    Haselkorn, Robert
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Genome Erosion in a Nitrogen-Fixing Vertically Transmitted Endosymbiotic Multicellular Cyanobacterium2010In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 5, no 7, article id e11486Article in journal (Refereed)
    Abstract [en]

    Background: An ancient cyanobacterial incorporation into a eukaryotic organism led to the evolution of plastids (chloroplasts) and subsequently to the origin of the plant kingdom. The underlying mechanism and the identities of the partners in this monophyletic event remain elusive.

    Methodology/Principal Findings: To shed light on this evolutionary process, we sequenced the genome of a cyanobacterium residing extracellularly in an endosymbiosis with a plant, the water-fern Azolla filiculoides Lam. This symbiosis was selected as it has characters which make it unique among extant cyanobacterial plant symbioses: the cyanobacterium lacks autonomous growth and is vertically transmitted between plant generations. Our results reveal features of evolutionary significance. The genome is in an eroding state, evidenced by a large proportion of pseudogenes (31.2%) and a high frequency of transposable elements (,600) scattered throughout the genome. Pseudogenization is found in genes such as the replication initiator dnaA and DNA repair genes, considered essential to free-living cyanobacteria. For some functional categories of genes pseudogenes are more prevalent than functional genes. Loss of function is apparent even within the ‘core’ gene categories of bacteria, such as genes involved in glycolysis and nutrient uptake. In contrast, serving as a critical source of nitrogen for the host, genes related to metabolic processes such as cell differentiation and nitrogen-fixation are well preserved.

    Conclusions/Significance: This is the first finding of genome degradation in a plant symbiont and phenotypically complex cyanobacterium and one of only a few extracellular endosymbionts described showing signs of reductive genome evolution. Our findings suggest an ongoing selective streamlining of this cyanobacterial genome which has resulted in an organism devoted to nitrogen fixation and devoid of autonomous growth. The cyanobacterial symbiont of Azolla can thus be considered at the initial phase of a transition from free-living organism to a nitrogen-fixing plant entity, a transition process which may mimic what drove the evolution of chloroplasts from a cyanobacterial ancestor.

  • 50.
    Sandh, Gustaf
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Botany.
    Díez, Beatriz
    Stockholm University, Faculty of Science, Department of Botany.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Temporal separation of cell division and diazotrophy in the marine diazotrophic cyanobacterium Trichodesmium erythraeum IMS1012009In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 295, no 2, p. 281-288Article in journal (Refereed)
    Abstract [en]

    Examination of the diurnal patterns of basic cellular processes in the marine nonheterocystous diazotrophic cyanobacterium Trichodesmium revealed that the division of cells occurred throughout the diurnal cycle, but that it oscillated and peaked at an early stage in the dark period. Transcription of the early cell division gene ftsZ and the occurrence of the FtsZ protein showed a similar diurnal rhythmicity that preceded the division of cells. DNA replication (dnaA gene transcription) occurred before the transcription of ftsZ and hetR, the latter encoding the key heterocyst differentiation protein. Transcription of ftsZ and hetR in turn preceded the development of the nitrogen-fixing diazocytes and nifH transcription, and were at the minimum when diazotrophy was at the maximum. The nifH gene transcription showed a negative correlation to the circadian clock gene kaiC. Together, the data show a temporal separation between cell division and diazotrophy on a diurnal basis.

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