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Ammonium ions inhibit nitrogen fixation but do not affect heterocyst frequency in the bloom-forming cyanobacterium Nodularia spumigena strain AV1.
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
2007 (English)In: Microbiology, ISSN 1350-0872, Vol. 153, no Pt 11, 3704-3712 p.Article in journal (Refereed) Published
Abstract [en]

In the presence of ammonium ion, Nodularia spumigena strain AV1, a filamentous, heterocystous cyanobacterium isolated from the Baltic Sea, lost aerobic nitrogen-fixation activity while maintaining heterocyst frequency along the filaments. Real-time RT-PCR showed that the expression of nifH (encoding the dinitrogenase reductase component of the nitrogenase enzyme) was suppressed and the levels of NifH protein decreased dramatically in response to treatment with ammonium. On the other hand, ntcA (encoding the global nitrogen regulator in cyanobacteria) and hetR (the key regulatory gene in heterocyst differentiation) were expressed and their expression patterns were not affected by the treatment with ammonium. These data demonstrate that N. spumigena strain AV1 maintains heterocyst frequency along the filaments in the presence of ammonium and in the absence of detectable N2-fixation activity.

Place, publisher, year, edition, pages
2007. Vol. 153, no Pt 11, 3704-3712 p.
URN: urn:nbn:se:su:diva-21072DOI: 10.1099/mic.0.2007/007849-0ISI: 000251096800009PubMedID: 17975078OAI: diva2:187598
Available from: 2007-12-05 Created: 2007-12-05 Last updated: 2009-09-01Bibliographically approved
In thesis
1. Functional genomics of the Baltic Sea cyanobacterium Nodularia spumigena in relation to nitrogen fixation, heterocyst differentiation and toxin production
Open this publication in new window or tab >>Functional genomics of the Baltic Sea cyanobacterium Nodularia spumigena in relation to nitrogen fixation, heterocyst differentiation and toxin production
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nodularia spumigena is a filamentous, heterocystous cyanobacterium that dominates the annual, toxic cyanobacterial blooms in the Baltic Sea. The blooms are believed to have increased in recent years, due to eutrophication by phosphate and/or nitrogen. Toxicity of these blooms is well-documented and attributed to the hepatotoxin nodularin. The focus of this study was to characterize nitrogen fixation and toxin production of Nodularia spumigena, in response to various levels of combined nitrogen and phosphate. In the presence of combined nitrogen, several Nodularia spumigena strains lost aerobic nitrogen fixation activity while the heterocyst frequency along the filaments remained unchanged. The expression of nifH dropped in response to the treatment, while the expression patterns of ntcA and hetR (key genes controlling heterocyst differentiation) were not affected. It is therefore concluded that in Nodularia, nitrogen fixation and heterocyst differentiation are uncoupled. Protein profiling during ammonium supplementation revealed differential expression of 28 proteins. Proteins involved in energy metabolism, carbon and nitrogen fixation were down-regulated during ammonium supplementation while stress-related proteins were up-regulated, further indicating that N. spumigena does not benefit from ammonium supplementation. Analysis of the nodularin synthetase (nda) gene expression demonstrated an increase of all the nine nda genes upon phosphate depletion and decrease of expression in the presence of combined nitrogen. In contrast to shifts in expression, the intra- and extracellular nodularin concentrations did not vary significantly, suggesting a transcriptionally-independent regulation of nodularin biosynthesis. Together, these data suggest that neither nitrogen nor phosphate alone, especially the low levels encountered in the Baltic Sea, affects heterocyst formation and nodularin biosynthesis.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University, 2009. 61 p.
cyanobacteria, Nodularia, nitrogen fixation, heterocyst, nitrogenase, ammonium, phosphate, nodularin, Baltic Sea
National Category
Research subject
Plant Physiology
urn:nbn:se:su:diva-29495 (URN)978-91-7155-935-7 (ISBN)
Public defence
2009-10-02, Föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 10:00 (English)
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript. Paper 5: ManuscriptAvailable from: 2009-09-10 Created: 2009-09-01 Last updated: 2009-09-01Bibliographically approved

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