volcanii ( 5, 10, 11).Īrchaea usually possess characteristics similar to those of bacteria in terms of metabolism, whereas their genetic processes, including replication, transcription, and translation, have been considered to be closer to those of eukaryotes than those of bacteria ( 12, 13). The DMSO reductase genes dmsABCD, which are homologous to the bacterial counterparts present in Escherichia coli, are also found in H. However, because of the lack of the N 2O reductase gene, the end product of denitrification by H. Similar to bacterial denitrification, the denitrifying process in archaea proceeds by successive reactions catalyzed by the redox enzymes nitrate reductase, nitrite reductase, NO reductase, and N 2O reductase ( 6, – 8). volcanii is a facultative anaerobic microorganism that can grow by denitrification (nitrate respiration), dimethyl sulfoxide (DMSO) respiration, or fumarate respiration under anaerobic conditions ( 1, – 5). Haloferax volcanii, an extreme haloarchaeon isolated from the Dead Sea, has been evaluated as a model organism of this type of extremophile ( 1, 2). The haloarchaeon-specific regulator NarO, which activates denitrification under anaerobic conditions, is suggested to be involved in the nitrate-responsive suppression of DMSO respiration. The results of transcriptome analysis, growth phenotyping, and reporter assays indicated that DMSO respiration is suppressed in response to nitrate in H. In facultative anaerobic bacteria that can grow by both nitrate respiration and DMSO respiration, nitrate respiration is preferentially induced when both nitrate and DMSO are available as the respiratory substrates. IMPORTANCE Haloferax volcanii can grow anaerobically by denitrification (nitrate respiration) or DMSO respiration. This is the first report to show that a regulatory mechanism that suppresses DMSO respiration in response to nitrate exists not only in bacteria but also in haloarchaea. Nitrate-responsive suppression of DMSO respiration is known in several bacteria such as Escherichia coli and photosynthetic Rhodobacter species. #Mosaic pro 1.0.10 ActivatorNarO has been identified as an activator of denitrification-related genes in response to anaerobic conditions, and here, we found that NarO is also involved in nitrate-responsive suppression of the dms operon. In contrast, the anaerobic growth of the Δ dmsR mutant by denitrification was little affected by the addition of DMSO. A reporter assay demonstrated that the transcription of the dms operon was suppressed by nitrate. volcanii by DMSO respiration was inhibited at nitrate concentrations of <1 mM, whereas nitrate-responsive growth inhibition was not observed in the Δ narO mutant. volcanii indicated extensive changes in gene expression involving the activation of denitrification, suppression of DMSO respiration, and conversion of the heme biosynthetic pathway under denitrifying conditions. Comparative transcriptome analysis of denitrifying and aerobic cells of H. Haloferax volcanii is a facultative anaerobic haloarchaeon that can grow using nitrate or dimethyl sulfoxide (DMSO) as a respiratory substrate under anaerobic conditions.
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