Nitrate reduction in Haloferax alexandrinus: the case of assimilatory nitrate reductase.
Haloferax alexandrinus Strain TM JCM 10717T= IFO 16590Tis an extreme halophilic archaeon able to produce significant amounts of canthaxanthin. Its genome sequence has been analysed in this work using bioinformatics tools available at Expasy in order to look for genes encoding nitrate reductase-like proteins: respiratory nitrate reductase (Nar) and/or assimilatory nitrate reductase (Nas). The ability of the cells to reduce nitrate under aerobic conditions was tested. The enzyme in charge of nitrate reduction under aerobic conditions (Nas) has been purified and characterised. It is a monomeric enzyme (72 ± 1.8 kDa) that requires high salt concentration for stability and activity. The optimum pH value for activity was 9.5. Effectiveness of different substrates, electron donors, cofactors and inhibitors was also reported. High nitrite concentrations were detected within the culture media during aerobic/microaerobic cells growth. The main conclusion from the results is that this haloarchaeon reduces nitrate aerobically thanks to Nas and may induce denitrification under anaerobic/microaerobic conditions using nitrate as electron acceptor. The study sheds light on the role played by haloarchaea in the biogeochemical cycle of nitrogen, paying special attention to nitrate reduction processes. Besides, it provides useful information for future attempts on microecological and biotechnological implications of haloarchaeal nitrate reductases.
Department of Biology, Faculty of Science, Anadolu University, 26470, Eskişehir, Turkey.
Volkan
V
Kilic
Department of Biology, Faculty of Science, Anadolu University, 26470, Eskişehir, Turkey.
Gözde Aydoğan
GA
Kilic
Department of Biology, Faculty of Science, Anadolu University, 26470, Eskişehir, Turkey.
Hatice Mehtap
HM
Kutlu
División de Bioquímica y Biología Molecular, Departamento de Agroquímica y Bioquímica, Facultad de Ciencias, Universidad de Alicante, Ap. 99, 03080, Alicante, Spain. rosa.martinez@ua.es.
Rosa María
RM
Martínez-Espinosa
D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism*; D004795:Enzyme Stability; D019621:Haloferax / Q000201:enzymology* / Q000378:metabolism; D009565:Nitrate Reductases / Q000737:chemistry / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D010084:Oxidation-Reduction; D013379:Substrate Specificity
D019843:Archaeal Proteins; D009566:Nitrates; D009565:Nitrate Reductases
Archaea; Assimilatory nitrate pathway; Denitrification; Halophiles; N-cycle; Nitrate reductase