title: Phosphate and oxygen limitation induce respiratory nitrate reductase 3 synthesis in stationary-phase mycelium of Streptomyces coelicolor A3(2).
abstract: The saprophytic actinobacterium Streptomyces coelicolor A3(2) requires oxygen for filamentous growth. Surprisingly, the bacterium also synthesizes three active respiratory nitrate reductases (Nar), which are believed to contribute to survival, or general fitness, of the bacterium in soil when oxygen becomes limiting. In this study, we analysed Nar3 and showed that activity of the enzyme is restricted to stationary-phase mycelium of S. coelicolor. Phosphate limitation was shown to be necessary for induction of enzyme synthesis. Nar3 synthesis was inhibited by inclusion of 20 mM phosphate in a defined 'switch assay' in which highly dispersed mycelium from exponentially growing cultures was shifted to neutral MOPS-glucose buffer to induce Nar3 synthesis and activity. Quantitative assessment of nar3 transcripts revealed a 30-fold induction of gene expression in stationary-phase mycelium. Transcript levels in stationary-phase mycelium incubated with phosphate were reduced by a little more than twofold, suggesting that the negative influence of phosphate on Nar3 synthesis was mainly at the post-transcriptional level. Furthermore, it was demonstrated that oxygen limitation was necessary to induce high levels of Nar3 activity. However, an abrupt shift from aerobic to anaerobic conditions prevented appearance of Nar3 activity. This suggests that the bacterium regulates Nar3 synthesis in response to the energy status of the mycelium. Nitrate had little impact on regulation of the Nar3 level. Together, these data identify Nar3 as a stationary-phase nitrate reductase in S. coelicolor and demonstrate that enzyme synthesis is induced in response to both phosphate limitation and hypoxia.
authors: Institute of Biology/Microbiology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle (Saale), Germany.
authors: Dörte
authors: D
authors: Falke
authors: Institute of Biology/Microbiology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle (Saale), Germany.
authors: Marco
authors: M
authors: Fischer
authors: Institute of Biology/Microbiology, Martin-Luther University Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120 Halle (Saale), Germany.
authors: R Gary
authors: RG
authors: Sawers
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D025282:Mycelium / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D050901:Nitrate Reductase / Q000096:biosynthesis / Q000235:genetics*; D010100:Oxygen / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D048372:Streptomyces coelicolor / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D010710:Phosphates; D050901:Nitrate Reductase; D010100:Oxygen