An HcpR homologue from Desulfovibrio desulfuricans and its possible role in nitrate reduction and nitrosative stress

The Escherichia coli CRP (cAMP receptor protein), is a global regulator of transcription that modulates gene expression by activation or repression at a range of promoters in E. coli. A major function is to regulate the selection of nutrients required for growth. The anaerobic sulfate-reducing bacterium Desulfovibrio desulfuricans ATCC27774 is capable of utilizing sulfate, nitrite and nitrate as terminal electron acceptors. In the presence of both sulfate and nitrate, sulfate is reduced preferentially despite nitrate being the thermodynamically more favourable electron acceptor. Three inverted repeat sequences upstream of the D. desulfuricans ATCC27774 nap (nitrate reduction in the periplasm) operon have high levels of similarity to the consensus sequence for the E. coli CRP DNA-binding site. In other Desulfovibrio species a putative CRP homologue, HcpR [regulator of hcp (hybrid cluster protein) transcription], has a predicted regulon comprising genes involved in sulfate reduction and nitrosative stress. The presence of CRP consensus sites within the D. desulfuricans ATCC27774 nap promoter prompted a search for CRP homologues in the genomes of sulfate-reducing bacteria. This revealed the presence of a potential CRP homologue that we predict binds to CRP consensus sites such as those of the nap operon. Furthermore, we predict that much of the core HcpR regulon predicted in other Desulfovibrio species is conserved in D. desulfuricans.