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  • 1. dos Reis, Fabio Bueno, Jr.
    et al.
    Simon, Marcelo F.
    Gross, Eduardo
    Boddey, Robert M.
    Elliott, Geoffrey N.
    Neto, Nicolau E.
    Loureiro, M. de Fatima
    de Queiroz, Luciano P.
    Scotti, Maria Rita
    Chen, Wen-Ming
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Rubio, Maria C.
    de Faria, Sergio M.
    Bontemps, Cyril
    Goi, Silvia R.
    Young, J. Peter W.
    Sprent, Janet I.
    James, Euan K.
    Nodulation and nitrogen fixation by Mimosa spp. in the Cerrado and Caatinga biomes of Brazil2010In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 186, no 4, p. 934-946Article in journal (Refereed)
    Abstract [en]

    P>An extensive survey of nodulation in the legume genus Mimosa was undertaken in two major biomes in Brazil, the Cerrado and the Caatinga, in both of which there are high degrees of endemicity of the genus. Nodules were collected from 67 of the 70 Mimosa spp. found. Thirteen of the species were newly reported as nodulating. Nodules were examined by light and electron microscopy, and all except for M. gatesiae had a structure typical of effective Mimosa nodules. The endosymbiotic bacteria in nodules from all of the Mimosa spp. were identified as Burkholderia via immunolabelling with an antibody against Burkholderia phymatum STM815. Twenty of the 23 Mimosa nodules tested were shown to contain nitrogenase by immunolabelling with an antibody to the nitrogenase Fe- (nifH) protein, and using the delta 15N (15N natural abundance) technique, contributions by biological N-2 fixation of up to 60% of total plant N were calculated for Caatinga Mimosa spp. It is concluded that nodulation in Mimosa is a generic character, and that the preferred symbionts of Brazilian species are Burkholderia. This is the first study to demonstrate N-2 fixation by beta-rhizobial symbioses in the field.

  • 2. Gumaelius, Lena
    et al.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Voss, Mirjam
    Outreach initiatives operated by universities for increasing interest in science and technology2016In: European Journal of Engineering Education, ISSN 0304-3797, E-ISSN 1469-5898, Vol. 41, no 6, p. 589-622Article in journal (Refereed)
    Abstract [en]

    Since the 1990s, the low number of students choosing to study science and technology in higher education has been on the societal agenda and many initiatives have been launched to promote awareness regarding career options. The initiatives particularly focus on increasing enrolment in the engineering programmes. This article describes and compares eight European initiatives that have been established and operated by universities (and in some cases through collaboration with other actors in society). Each initiative is summarised in a short essay that discusses motivation, organisation, pedagogical approach, and activities. The initiatives are characterised by comparing the driving forces behind their creation, how the initiative activities relate to the activities at the university, size based on the number of participants and cost per participant and pedagogical framework. There seem to be two main tracks for building outreach activities, one where outreach activities are based on the university’s normal activities, and one where outreach activities are designed specifically for the visiting students. 

  • 3.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Metabolic regulation of nitrogenase in Rhodospirillum rubrum: studies on DRAG and DRAT, the regulatory proteins of dinitrogenase reductase1998Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Nitrogen fixation is catalyzed by nitrogenase, in an ATP-dependent reaction where dinitrogen is reduced to ammonium. Nitrogenase is a protein complex consisting of two proteins; dinitrogenase and dinitrogenase reductase and the reaction is only carried out by prokaryotes. In the photosynthetic bacterium, Rhodospirillum rubrum, nitrogen fixation is regulated at both a genetic and a metabolic level. The metabolic regulation is excerted through post-translational modification of dinitrogenase reductase, causing inactivation of the enzyme when so called switch-off effectors are added. The post-translational modification has been shown to be an ADP-ribosylation on Arg-101 of dinitrogenase reductase. The regulatory proteins are; dinitrogenase reductase ADP-ribosyl transferase (DRAT), catalyzing modification and dinitrogenase reductase activating glycohydrolase (DRAG) catalyzing demodification. Both DRAG and DRAT are subjected to post-translational regulation in the cell. The internal signals for this regulation are still not identified and have been the focus of this thesis.

    By changing the concentration of NAD+ in R.rubrum a reversible decrease in nitrogenase activity could be observed. This decrease in activity was shown to be correlated to a post-translational modification of dinitrogenase reductase by SDS-PAGE and Western blot. The modification is catalyzed by DRAT since studies on a DRAT- mutant show no response at all to additional NAD+. Shortening the switch-off period by addition of NADH generating compounds, confirmed that a change in NAD+ /NADH ratio affects the duration of the switch-off period. Using in vivo fluorometry to study the effect of changes in the NAD+ concentration when nitrogenous switch-off effectors were added, showed that ammonium and glutamine momentarily change the concentration of NAD+. On the basis of these results we suggest that the signal pathway for DRAT activation involves changes in the concentration of NAD+.

    The membrane associated DRAG is shown to be released by treating the chromatophores with MgGDP, similar treatment with MgGTP, MgATP or MgADP did not result in such a release. Upto 40% of DRAG activity can be found in the supernatant compared to 0.5 M NaCl treated membranes. The chromatophore membranes are shown to have GTPase activity with and without DRAG associated to the membranes indicating the presence of a GTP hydrolyzing protein in the chromatophore membrane. Crosslinking studies demonstrated a high molecular weight complex, that crossreacted with DRAG antibodies.

    The regulation of DRAG is suggested by us to be mediated by the chromatophore membrane possibly involving a protein complex with GTPase activity. DRAG is suggested to be active in its soluble form and inactive when bound to the membranes.

  • 4.
    Selao, Tiago T.
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Comparative proteomic studies in Rhodospirillum rubrum grown under different nitrogen conditions2008In: Journal of Proteome Research, ISSN 1535-3893, E-ISSN 1535-3907, Vol. 7, no 8, p. 3267-3275Article in journal (Refereed)
    Abstract [en]

    Forty-four differentially expressed proteins have been identified in the photosynthetic diazotroph Rhodospirillum rubrum grown anaerobic and photoheterotrophically, with different nitrogen sources, using 2D-PAGE and MALDI-TOF, from gels containing an average of 679 ± 52 (in N+) and 619 ± 37 (in N−) protein spots for each gel. A higher level of expression was found under nitrogen-rich growth, for proteins involved in carbon metabolism (reductive tricarboxylic acid cycle, CO2 fixation, and poly-β-hydroxybutyrate metabolism) and amino acid metabolism. The key enzymes RuBisCO and α-ketoglutarate synthase were found to be present in higher amounts in nitrogen-rich conditions. Ntr and Nif regulated proteins, such as glutamine synthetase and nitrogenase, were, as expected, induced under nitrogen-fixing conditions and glutamate dehydrogenase was down regulated. A novel 2Fe-2S ferredoxin with unknown function was identified from nitrogen-fixing cultures. In addition to differential expression, two of the identified proteins revealed variable pI values in response to the nitrogen source used.

  • 5.
    Selao, Tiago Toscano
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Branca, Rui
    Chae, Pil Seok
    Lehtio, Janne
    Gellman, Samuel H.
    Rasmussen, Sören G. F.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Identification of Chromatophore Membrane Protein Complexes Formed under Different Nitrogen Availability Conditions in Rhodospirillum rubrum2011In: Journal of Proteome Research, ISSN 1535-3893, E-ISSN 1535-3907, Vol. 10, no 6, p. 2703-2714Article in journal (Refereed)
    Abstract [en]

    The chromatophore membrane of the photosynthetic diazotroph Rhodospirillum rubrum is of vital importance for a number of central processes, including nitrogen fixation. Using a novel amphiphile, we have identified protein complexes present under different nitrogen availability conditions by the use of two-dimensional Blue Native/SDS-PAGE and NSI-LC-LTQ-Orbitrap mass spectrometry. We have identified several membrane protein complexes, including components of the ATP synthase, reaction center, light harvesting, and NADH dehydrogenase complexes. Additionally, we have identified differentially expressed proteins, such as subunits of the succinate dehydrogenase complex and other TCA cycle enzymes that are usually found in the cytosol, thus hinting at a possible association to the membrane in response to nitrogen deficiency. We propose a redox sensing mechanism that can influence the membrane subproteome in response to nitrogen availability.

  • 6.
    Selao, Tiago Toscano
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Edgren, Tomas
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wang, He
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Effect of pyruvate on the metabolic regulation of nitrogenase activity in Rhodospirillum rubrum in darkness2011In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080, Vol. 157, p. 1834-1840Article in journal (Refereed)
    Abstract [en]

    Rhodospirillum rubrum, a photosynthetic diazotroph, is able to regulate nitrogenase activity in response to environmental factors such as ammonium ions or darkness, the so-called switch-off effect. This is due to reversible modification of the Fe-protein, one of the two components of nitrogenase. The signal transduction pathway(s) in this regulatory mechanism is not fully understood, especially not in response to darkness. We have previously shown that the switch-off response and metabolic state differ between cells grown with dinitrogen or glutamate as the nitrogen source, although both represent poor nitrogen sources. In this study we show that pyruvate affects the response to darkness in cultures grown with glutamate as nitrogen source, leading to a response similar to that in cultures grown with dinitrogen. The effects are related to protein uridylylation and glutamine synthetase activity. We also show that pyruvate induces de novo protein synthesis and that inhibition of pyruvate formate-lyase leads to loss of nitrogenase activity in the dark.

  • 7.
    Selao, Tiago Toscano
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Edgren, Tomas
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wang, He
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    The effect of pyruvate on the metabolic regulation of nitrogenase activity in Rhodospirillum rubrum with darkness as switch-off effector2010In: Microbiology, ISSN 1350-0872, E-ISSN 1465-2080Article in journal (Refereed)
    Abstract [en]

    Rhodospirillum rubrum, a photosynthetic diazotroph, is able to regulate nitrogenase activity in response to environmental factors such as ammonium ions or darkness – the so-called switch-off effect. This is due to reversible modification of the Fe-protein one of the two components of nitrogenase. The signal transduction pathway(s) in this regulatory mechanism is not fully understood, especially not in the response to darkness. We have previously shown that the switch-off response and metabolic state differ between cells grown with dinitrogen or glutamate as nitrogen source, although both represent poor nitrogen sources. In this study we show that addition of pyruvate to cultures grown with glutamate as nitrogen source will lead to a switch-off response that is similar to that in cultures grown with dinitrogen. The effects are related to PII protein uridylylation and GS activity. We also show that pyruvate induces de novo protein synthesis and that pyruvate formate-lyase activity is required for activity in the dark.

  • 8.
    Teixeira, Pedro Filipe
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Selao, Tiago Toscano
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Henriksson, Veronika
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Wang, He
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Diazotrophic growth of Rhodospirillum rubrum with 2-oxoglutarate as sole carbon source affects the regulation of nitrogen metabolism as well as the soluble proteome2010In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123, Vol. 161, no 8, p. 651-659Article in journal (Refereed)
    Abstract [en]

    2-Oxoglutarate plays a central role as a signal in the regulation of nitrogen metabolism in the phototrophic diazotroph Rhodospirillum rubrum. In order to further study the role of this metabolite, we have constructed an R. rubrum strain that has the capacity to grow on 2-oxoglutarate as sole carbon source, in contrast to wild-type R. rubrum. This strain has the same growth characteristics as wild-type with malate as carbon source, but showed clear metabolic differences when 2-oxoglutarate was used. Among other things, the regulation of nitrogen metabolism is altered, which can be related to different modification profiles of the regulatory PII proteins.

  • 9.
    Vintila, Simina
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Selao, Tiago
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Noren, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Stockholm University, Faculty of Science, Department of Botany.
    Characterization of nifH gene expression, modification and rearrangement in Nodularia spumigena strain AV12011In: FEMS Microbiology Ecology, ISSN 0168-6496, E-ISSN 1574-6941, Vol. 77, no 2, p. 449-459Article in journal (Refereed)
    Abstract [en]

    The annually reoccurring blooms that characterize the surface waters of the Baltic Sea are dominated by filamentous, heterocystous cyanobacteria such as Nodularia spumigena. In a previous study, we have demonstrated that N. spumigena strain AV1 differentiates heterocysts in the absence of detectable nitrogen fixation activity, an unusual physiological trait that is clearly distinct from other well-studied cyanobacteria. To further analyze the uncoupling between these two processes, we analyzed the gene expression and modification of the nitrogenase enzyme (the enzyme responsible for nitrogen fixation) in N. spumigena AV1, as well as in several other N. spumigena strains. Here, we demonstrate the occurrence of two nifH gene copies in N. spumigena strain AV1, only one of which is located in a complete nifHDK cluster and several NifH protein forms. Furthermore, we demonstrate the occurrence of a DNA rearrangement mechanism acting within the nifH gene copy located in the nifHDK cluster and present only in the strains exhibiting the previously reported uncoupling between heterocyst differentiation and nitrogen fixation processes. These data stress the existence of a distinct and complex regulatory circuit related to nitrogen fixation in this ecologically significant bloom-forming cyanobacterium.

  • 10.
    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.

  • 11.
    Wang, He
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Teixeira, Pedro
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Jonsson, Anders
    Vintila, Simina
    Norén, Agneta
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nordlund, Stefan
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Transcription of the PII-AmtB encoding operons in Rhodospirillum rubrum and studies of the functional role(s) of GlnB, GlnJ and AmtB1 in nitrogen metabolismArticle in journal (Refereed)
  • 12. 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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