Characterisation of chlorate reduction in the haloarchaeon Haloferax mediterranei

• Published in: Biochimica et biophysica acta Vol. 1850; no. 4; pp. 587 - 594
• Main Authors: Martínez-Espinosa, Rosa María, Richardson, David J., Bonete, María José
• Format: Journal Article
• Language: English
• Published: Netherlands 01.04.2015
• Subjects: active sites; Amino Acid Sequence; anaerobic conditions; cell membranes; Chlorates - metabolism; culture media; denitrification; enzyme activity; genes; Haloferax mediterranei; Haloferax mediterranei - metabolism; Hydrogen-Ion Concentration; ions; Molecular Sequence Data; Nitrate Reductase - metabolism; nitrates; Oxidation-Reduction; Oxidoreductases - metabolism; perchlorates; wastewater treatment; Archaeon; Respiratory nitrate reductase; Halophile; Anaerobic respiration; Chlorite dismutase; Chlorate reduction
• ISSN: 0304-4165; 0006-3002
• DOI: 10.1016/j.bbagen.2014.12.011

Haloferax mediterranei is a denitrifying haloarchaeon using nitrate as a respiratory electron acceptor under anaerobic conditions in a reaction catalysed by pNarGH. Other ions such as bromate, perchlorate and chlorate can also be reduced. Hfx. mediterranei cells were grown anaerobically with nitrate as electron acceptor and chlorate reductase activity measured in whole cells and purified nitrate reductase. No genes encoding (per)chlorate reductases have been detected either in the Hfx. mediterranei genome or in other haloarchaea. However, a gene encoding a chlorite dismutase that is predicted to be exported across the cytoplasmic membrane has been identified in Hfx. mediterranei genome. Cells did not grow anaerobically in presence of chlorate as the unique electron acceptor. However, cells anaerobically grown with nitrate and then transferred to chlorate-containing growth medium can grow a few generations. Chlorate reduction by the whole cells, as well as by pure pNarGH, has been characterised. No clear chlorite dismutase activity could be detected. Hfx. mediterranei pNarGH has its active site on the outer-face of the cytoplasmic membrane and reacts with chlorate and perchlorate. Biochemical characterisation of this enzymatic activity suggests that Hfx. mediterranei or its pure pNarGH could be of great interest for waste water treatments or to better understand biological chlorate reduction in early Earth or Martian environments. Some archaea species reduce (per)chlorate. However, results here presented as well as those recently reported by Liebensteiner and co-workers [1] suggest that complete perchlorate reduction in archaea follows different rules in terms of biological reactions.