title: Ammonium ions inhibit nitrogen fixation but do not affect heterocyst frequency in the bloom-forming cyanobacterium Nodularia spumigena strain AV1.
abstract: 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.
authors.affiliation: Department of Botany, Stockholm University, Stockholm, Sweden.
authors.forename: Simina
authors.initials: S
authors.lastname: Vintila
authors.affiliation: Department of Botany, Stockholm University, Stockholm, Sweden.
authors.forename: Rehab
authors.initials: R
authors.lastname: El-Shehawy
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003470:Culture Media; D004269:DNA, Bacterial / Q000032:analysis / Q000302:isolation & purification; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000187:drug effects*; D046932:Nodularia / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development* / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D004269:DNA, Bacterial; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; C067403:HetR protein, Bacteria; D010088:Oxidoreductases; C029130:nitrogenase reductase