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  • 1.
    Caputo, Andrea
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Nylander, Johan A. A.
    Foster, Rachel Ann
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    The genetic diversity and evolution of diatom-diazotroph associations highlights traits favoring symbiont integration2019In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 366, no 2, article id fny297Article in journal (Refereed)
    Abstract [en]

    Diatom diazotroph associations (DDAs) are a widespread marine planktonic symbiosis between several diatom genera and di-nitrogen (N2)-fixing bacteria. Combining single cell confocal microscopy observations and molecular genetic approaches on individual field collected cells, we determined the phylogenetic diversity, distribution and evolution of the DDAs. Confocal analyses coupled with 3-D imaging re-evaluated the cellular location of DDA symbionts. DDA diversity was resolved by paired gene sequencing (18S rRNA and rbcL genes, 16S rRNA and nifH genes). A survey using the newly acquired sequences against public databases found sequences with high similarity (99–100%) to either host (18S rRNA) or symbiont (16S rRNA) in atypical regions for DDAs (high latitudes, anoxic basin and copepod gut). Concatenated phylogenies were congruent for the host and cyanobacteria sequences and implied co-evolution. Time-calibrated trees dated the appearance of N2 fixing planktonic symbiosis from 100–50Mya and were consistent with the symbiont cellular location: symbioses with internal partners are more ancient. An ancestral state reconstruction traced the evolution of traits in DDAs and highlight that the adaptive radiation to the marine environment was likely facilitated by the symbiosis. Our results present the evolutionary nature of DDAs and provide new genetic and phenotypic information for these biogeochemically relevant populations.

  • 2. 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).

  • 3.
    Karyolaimos, Alexandros
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Ampah-Korsah, Henry
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Zhang, Zhe
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    de Gier, Jan-Willem
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Shaping Escherichia coli for recombinant membrane protein production2018In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 365, no 15, article id fny152Article, review/survey (Refereed)
    Abstract [en]

    The bacterium Escherichia coli has been widely used for the production of both pro- and eukaryotic membrane proteins. Usually, a set of standard strains as well as different culture setups and induction regimes are screened for to enhance production yields. However, on a limited scale, E. coli strains have been isolated for recombinant helical bundle membrane protein production using both selection- and engineering-based approaches. Here, we discuss how such approaches have been used so far to shape E. coli for the production of these recombinant membrane proteins and may be used in the future to further enhance production yields.

  • 4. 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).

  • 5.
    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.

  • 6.
    Wang, He
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Franke, Claudia C.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Reversible membrane association of dinitrogenase reductase activating glycohydrolase in the regulation of nitrogenase activity in Rhodospirillum rubrum; dependence on GlnJ and AmtB12005In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 253, no 2, p. 273-279Article in journal (Refereed)
    Abstract [en]

    In the photosynthetic bacterium Rhodospirillum rubrum nitrogenase activity is regulated by reversible ADP-ribosylation of dinitrogenase reductase in response to external so called “switch-off” effectors. Activation of the modified, inactive form is catalyzed by dinitrogenase reductase activating glycohydrolase (DRAG) which removes the ADP-ribose moiety. This study addresses the signal transduction between external effectors and DRAG. R. rubrum, wild-type and PII mutant strains, were studied with respect to DRAG localization. We conclude that GlnJ clearly has an effect on the association of DRAG to the membrane in agreement with the effect on regulation of nitrogenase activity. Furthermore, we have generated a R. rubrum mutant lacking the putative ammonium transporter AmtB1 which was shown not to respond to “switch-off” effectors; no loss of nitrogenase activity and no ADP-ribosylation. Interestingly, DRAG was mainly localized to the cytosol in this mutant. Overall the results support our model in which association to the membrane is part of the mechanism regulating DRAG activity.

  • 7. Wang, Helen
    et al.
    Waluk, Dominik
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Dixon, Ray
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Energy shifts induce membrane sequestration of DraG in Rhodospirillum rubrum independent of the ammonium transporters and diazotrophic conditions2018In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 365, no 16, article id fny176Article in journal (Refereed)
    Abstract [en]

    Metabolic regulation of Rhodospirillum rubrum nitrogenase is mediated at the post-translational level by the enzymes DraT and DraG when subjected to changes in nitrogen or energy status. DraT is activated during switch-off, while DraG is inactivated by reversible membrane association. We confirm here that the ammonium transporter, AmtB1, rather than its paralog AmtB2, is required for ammonium induced switch-off. Amongst several substitutions at the N100 position in DraG, only N100K failed to locate to the membrane following ammonium shock, suggesting loss of interaction through charge repulsion. When switch-off was induced by lowering energy levels, either by darkness during photosynthetic growth or oxygen depletion under respiratory conditions, reversible membrane sequestration of DraG was independent of AmtB proteins and occurred even under non-diazotrophic conditions. We propose that under these conditions, changes in redox status or possibly membrane potential induce interactions between DraG and another membrane protein in response to the energy status.

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