title: Nitrate/nitrite assimilation system of the marine picoplanktonic cyanobacterium Synechococcus sp. strain WH 8103: effect of nitrogen source and availability on gene expression.
abstract: The genes encoding the structural components of the nitrate/nitrite assimilation system of the oceanic cyanobacterium Synechococcus sp. strain WH 8103 were cloned and characterized. The genes encoding nitrate reductase (narB) and nitrite reductase (nirA) are clustered on the chromosome but are organized in separate transcriptional units. Upstream of narB is a homologue of nrtP that encodes a nitrate/nitrite-bispecific permease rather than the components of an ABC-type nitrate transporter found in freshwater cyanobacteria. Unusually, neither nirA nor ntcA (encoding a positive transcription factor of genes subject to nitrogen control) were found to be tightly regulated by ammonium. Furthermore, transcription of glnA (encoding glutamine synthetase) is up-regulated in ammonium-grown cells, highlighting significant differences in nitrogen control in this cyanobacterium. Nitrogen depletion led to the transient up-regulation of ntcA, nirA, nrtP, narB, and glnA in what appears to be an NtcA-dependent manner. The NtcA-like promoters found upstream of nirA, nrtP, and narB all differ in sequence from the canonical NtcA promoter established for other cyanobacteria, and in the case of nirA, the NtcA-like promoter was functional only in cells deprived of combined nitrogen. The ecological implications of these findings are discussed in the context of the oligotrophic nature of oceanic surface waters in which Synechococcus spp. thrive.
authors.affiliation: School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom.
authors.forename: Clare
authors.initials: C
authors.lastname: Bird
authors.forename: Michael
authors.initials: M
authors.lastname: Wyman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D009572:Nitrite Reductases / Q000235:genetics / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010933:Plankton / Q000235:genetics / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012623:Seawater / Q000382:microbiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D009566:Nitrates; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; C075617:ntcA protein, Synechococcus; D009565:Nitrate Reductases; D009572:Nitrite Reductases; D050901:Nitrate Reductase; D009584:Nitrogen