Regulation of Hydrogenase Gene Expression

Abstract

Photosynthetic bacteria contain various types of [NiFe]-hydrogenases. The most widespread are respiratory uptake hydrogenases that are usually co-synthesized with nitrogenase. Hydrogenase synthesis responds to envi- ronmental signals such as H2, O2, CO. In Rhodobacter species and Rhodopseudomonas palustris, a regulatory [NiFe]-hydrogenase, HupUV, is the direct H2 sensor of the H2 regulatory pathway. It transfers the signal to a two-component regulatory system, which comprises the soluble histidine kinase HupT/HoxJ and the response regulator HupR/HoxA. The transcription factor HupR/HoxA activates the transcription of hydrogenase genes in its nonphosphorylated form. In Rhodospirillum rubrum, the transcriptional regulator CooA, which senses CO and the redox state, activates the synthesis of a CO-tolerant hydrogenase under anaerobic conditions. In Thiocapsa roseopersicina, FnrT activates anaerobic induction of the Hyn hydrogenase. In Rhodobacter species and in Rhodopseudomonas palustris, hydrogenase synthesis is also under the negative control of the redox- responding global two-component regulatory system, RegB/PrrB/RegS-RegA/Prra/RegR.