Expression of uptake hydrogenase and molybdenum nitrogenase in Rhodobacter capsulatus is coregulated by the RegB-RegA two-component regulatory system.
Purple photosynthetic bacteria are capable of generating cellular energy from several sources, including photosynthesis, respiration, and H(2) oxidation. Under nutrient-limiting conditions, cellular energy can be used to assimilate carbon and nitrogen. This study provides the first evidence of a molecular link for the coregulation of nitrogenase and hydrogenase biosynthesis in an anoxygenic photosynthetic bacterium. We demonstrated that molybdenum nitrogenase biosynthesis is under the control of the RegB-RegA two-component regulatory system in Rhodobacter capsulatus. Footprint analyses and in vivo transcription studies showed that RegA indirectly activates nitrogenase synthesis by binding to and activating the expression of nifA2, which encodes one of the two functional copies of the nif-specific transcriptional activator, NifA. Expression of nifA2 but not nifA1 is reduced in the reg mutants up to eightfold under derepressing conditions and is also reduced under repressing conditions. Thus, although NtrC is absolutely required for nifA2 expression, RegA acts as a coactivator of nifA2. We also demonstrated that in reg mutants, [NiFe]hydrogenase synthesis and activity are increased up to sixfold. RegA binds to the promoter of the hydrogenase gene operon and therefore directly represses its expression. Thus, the RegB-RegA system controls such diverse processes as energy-generating photosynthesis and H(2) oxidation, as well as the energy-demanding processes of N(2) fixation and CO(2) assimilation.
Elsen
S
S
Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
Dischert
W
W
Colbeau
A
A
Bauer
C E
CE
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D004269:DNA, Bacterial; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D008969:Molecular Sequence Data; D009591:Nitrogenase / Q000235:genetics* / Q000378:metabolism; D010088:Oxidoreductases / Q000096:biosynthesis / Q000235:genetics*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000201:enzymology* / Q000235:genetics; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation
D001426:Bacterial Proteins; D004269:DNA, Bacterial; C061338:NifA protein, Bacteria; D045322:Photosynthetic Reaction Center Complex Proteins; D011993:Recombinant Fusion Proteins; C072722:RegA protein, Bacteria; C091081:RegB protein, Rhodobacter; D014157:Transcription Factors; D010088:Oxidoreductases; C029746:uptake hydrogenase; D009591:Nitrogenase; C029130:nitrogenase reductase; D011494:Protein Kinases