Organization of methylamine utilization genes (mau) in ‘Methylobacillus flagellatum’ KT and analysis of mau mutants

Abstract

The organization of genes involved in utilization of methylamine (mau genes) was studied in the obligate methylotroph ‘Methylobacillus flagellatum’ KT. Nine open reading frames were identified as corresponding to the genes mauFBEDAGLMN. In addition, an open reading frame (orf-1) encoding a polypeptide with unknown function was identified upstream of the mau gene cluster. Subclones of the ‘M. flagellatum’ KT gene cluster were used for complementation of a series of chemically induced mau mutants of ‘M. flagellatum’ KT. Mutants in mauF, mauB, mauEID, mauA, mauG, mauL and mauM were identified. Two mutants (mau-18 and mau-19) were not complemented by the known mau genes. Since none of the chemically induced mutants studied had a defect in orf-1 or mauN, insertion mutants in these genes were constructed. Phenotypically the mutants fell into three groups. The mauF, mauB, mauE/D, mauA, mauG, mauL and mauM mutants do not grow on methylamine as a source of carbon and lack methylamine dehydrogenase activity, but they synthesize both the large and the small subunit polypeptides albeit at different ratios. The mau-18 and mau-19 mutants do not grow on methylamine as a source of carbon, and lack both methylamine dehydrogenase activity and the methylamine dehydrogenase subunits. The orf-1 and mauN mutants grow on methylamine as a source of carbon and synthesize wild-type levels of methylamine dehydrogenase. It has been shown earlier that the product of the mauM gene is not required for synthesis of active methylamine dehydrogenase in Methylobacterium extorquens AM1 and Paracoccus denitrificans. However, MauM is required for synthesis of functional methylamine dehydrogenase in ‘M. flagellatum’.