PMID: 11931554Apr 5, 2002Paper

Regulation of nitrogen fixation in the phototrophic purple bacterium Rhodobacter capsulatus

Journal of Molecular Microbiology and Biotechnology
Bernd MasepohlWerner Klipp

Abstract

In R. capsulatus synthesis and activity of the molybdenum and the alternative nitrogenase is controlled at three levels by the environmental factors ammonium, molybdenum, light, and oxygen. At the first level, transcription of the nifA1, nifA2, and anfA genes--which encode the transcriptional activators of all other nif and anf genes, respectively--is controlled by the Ntr system in dependence on ammonium availability. Mutations in ginB (coding for the signal transduction protein PII) result in significant expression of nifA and anfA in the presence of ammonium. In contrast to GlnB, the PII-paralogue GlnK is not involved in the Ntr signal transduction mechanism. In addition to ammonium control, transcription of anfA is inhibited by traces of molybdenum via the molybdate-dependent repressor proteins MopA and MopB. At the second level of regulation, activity of NifA1, NifA2, and AnfA is inhibited by ammonium in an NtrC-independent manner. This post-translational ammonium control of NifA activity is partially released in the absence of GlnK, and completely abolished in a glnB/glnK double mutant. In contrast, AnfA activity is still inhibited by ammonium in the glnB/glnK mutant background. At the third level of regulation, both GlnB...Continue Reading

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