Insights into denitrification in Methylotenera mobilis from denitrification pathway and methanol metabolism mutants.

We investigated phenotypes of mutants of Methylotenera mobilis JLW8 with lesions in genes predicted to encode functions of the denitrification pathway, as well as mutants with mutations in methanol dehydrogenase-like structural genes xoxF1 and xoxF2, in order to obtain insights into denitrification and methanol metabolism by this bacterium. By monitoring the accumulation of nitrous oxide, we demonstrate that a periplasmic nitrate reductase, NAD(P)-linked and copper-containing nitrite reductases, and a nitric oxide reductase are involved in the denitrification pathway and that the pathway must be operational in aerobic conditions. However, only the assimilatory branch of the denitrification pathway was essential for growth on methanol in nitrate-supplemented medium. Mutants with mutations in each of the two xoxF genes maintained their ability to grow on methanol, but not the double XoxF mutant, suggesting that XoxF proteins act as methanol dehydrogenase enzymes in M. mobilis JLW8. Reduced levels of nitrous oxide accumulated by the XoxF mutants compared to the wild type suggest that these enzymes must be capable of donating electrons for denitrification.