Anaerobic Growth of Haloarchaeon Haloferax volcanii by Denitrification Is Controlled by the Transcription Regulator NarO
Abstract
The extremely halophilic archaeon Haloferax volcanii grows anaerobically by denitrification. A putative DNA-binding protein, NarO, is encoded upstream of the respiratory nitrate reductase gene of H. volcanii. Disruption of the narO gene resulted in a loss of denitrifying growth of H. volcanii, and the expression of the recombinant NarO recovered the denitrification capacity. A novel CXnCXCX7C motif showing no remarkable similarities with known sequences was conserved in the N terminus of the NarO homologous proteins found in the haloarchaea. Restoration of the denitrifying growth was not achieved by expression of any mutant NarO in which any one of the four conserved cysteines was individually replaced by serine. A promoter assay experiment indicated that the narO gene was usually transcribed, regardless of whether it was cultivated under aerobic or anaerobic conditions. Transcription of the genes encoding the denitrifying enzymes nitrate reductase and nitrite reductase was activated under anaerobic conditions. A putative cis element was identified in the promoter sequence of haloarchaeal denitrifying genes. These results demonstrated a significant effect of NarO, probably due to its oxygen-sensing function, on the transcriptio...Continue Reading
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