title: 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 transcriptional activation of haloarchaeal denitrifying genes.
  
  
  OBJECTIVE
  H. volcanii is an extremely halophilic archaeon capable of anaerobic growth by denitrification. The regulatory mechanism of denitrification has been well understood in bacteria but remains unknown in archaea. In this work, we show that the helix-turn-helix (HTH)-type regulator NarO activates transcription of the denitrifying genes of H. volcanii under anaerobic conditions. A novel cysteine-rich motif, which is critical for transcriptional regulation, is present in NarO. A putative cis element was also identified in the promoter sequence of the haloarchaeal denitrifying genes.
authors.affiliation: Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hattori
authors.affiliation: Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan.
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Shiba
authors.affiliation: Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Ashiki
authors.affiliation: Department of Environment and Energy Systems, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan.
authors.forename: Takuma
authors.initials: T
authors.lastname: Araki
authors.affiliation: Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan.
authors.forename: Yoh-kow
authors.initials: YK
authors.lastname: Nagashima
authors.affiliation: Research Institute of Green Science and Technology, Shizuoka University, Shizuoka, Japan.
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Yoshimatsu
authors.affiliation: Department of Science, Graduate School of Integrated Science and Technology, Shizuoka University, Shizuoka, Japan Department of Environment and Energy Systems, Graduate School of Science and Technology, Shizuoka University, Shizuoka, Japan fujiwara.taketomo@shizuoka.ac.jp.
authors.forename: Taketomo
authors.initials: T
authors.lastname: Fujiwara
mesh_terms: D000595:Amino Acid Sequence; D000693:Anaerobiosis; D019843:Archaeal Proteins / Q000235:genetics / Q000378:metabolism*; D058440:Denitrification / Q000502:physiology; D019848:Gene Expression Regulation, Archaeal / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D019622:Haloferax volcanii / Q000502:physiology*; D008969:Molecular Sequence Data; D050901:Nitrate Reductase / Q000235:genetics / Q000378:metabolism; D010957:Plasmids; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D019843:Archaeal Proteins; D014157:Transcription Factors; D050901:Nitrate Reductase