title: Decoupling of ammonium regulation and ntcA transcription in the diazotrophic marine cyanobacterium Trichodesmium sp. IMS101.
abstract: Nitrogen (N) physiology in the marine cyanobacterium Trichodesmium IMS101 was studied along with transcript accumulation of the N-regulatory gene ntcA and of two of its target genes: napA (nitrate assimilation) and nifH (N(2) fixation). N(2) fixation was impaired in the presence of nitrite, nitrate and urea. Strain IMS101 was capable of growth on these combined N sources at <2 μM but growth rates declined at elevated concentrations. Assimilation of nitrate and urea was impaired in the presence of ammonium. Whereas ecologically relevant N concentrations (2-20 μM) suppressed growth and assimilation, much higher concentrations were required to affect transcript levels. Transcripts of nifH accumulated under nitrogen-fixing conditions; these transcript levels were maintained in the presence of nitrate (100 μM) and ammonium (20 μM). However, nifH transcript levels were below detection at ammonium concentrations >20 μM. napA mRNA was found at low levels in both N(2)-fixing and ammonium-utilizing filaments, and it accumulated in filaments grown with nitrate. The positive effect of nitrate on napA transcription was abolished by ammonium additions of >200 μM. This effect was restored upon addition of the glutamine synthetase inhibitor L-methionin-DL-sulfoximine. Surprisingly, ntcA transcript levels remained high in the presence of ammonium, even at elevated concentrations. These findings indicate that ammonium repression is decoupled from transcriptional activation of ntcA in Trichodesmium IMS101.
authors.affiliation: The Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA 02543, USA. apost@mbl.edu
authors.forename: Anton F
authors.initials: AF
authors.lastname: Post
authors.forename: Branko
authors.initials: B
authors.lastname: Rihtman
authors.forename: Qingfeng
authors.initials: Q
authors.lastname: Wang
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005974:Glutamate-Ammonia Ligase / Q000235:genetics; D009566:Nitrates / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D009603:Nitroso Compounds; D000644:Quaternary Ammonium Compounds / Q000378:metabolism* / Q000494:pharmacology; D053778:Thiazolidines; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014508:Urea / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D009566:Nitrates; D009573:Nitrites; D009603:Nitroso Compounds; D000644:Quaternary Ammonium Compounds; D053778:Thiazolidines; D014157:Transcription Factors; C040387:N-nitrosothiazolidine-4-carboxylic acid; D014508:Urea; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen