METHANESULFONATE UTILIZATION BY A NOVEL METHYLOTROPHIC BACTERIUM INVOLVES AN UNUSUAL MONOOXYGENASE

Methylotroph strain M2, isolated from soil, was capable of growth on m ethanesulphonic acid (MSA) as sole carbon and energy source. MSA was o xidized by cell suspensions with an MSA:oxygen stoichiometry of 1.0:2. 0, indicating complete conversion to carbon dioxide and sulphate. The presence of formaldehyde and formate dehydrogenases and hydroxypyruvat e reductase in MSA-grown bacteria indicated the production of formalde hyde from MSA (and its further oxidation for energy generation), and a ssimilation of formaldehyde by means of the serine pathway. Growth yie lds in MSA-limited chemostat culture were a function of dilution rate, with yield ranging from 7.0 g mol(-1) at D = 0.04 h(-1), to 14.6 at 0 .09 h(-1). MSA metabolism was not initiated by hydrolysis to produce e ither methane or methanol, but appears to be by an NADH-dependent meth anesulphonate monooxygenase, cleaving MSA into formaldehyde and sulphi te. The organism lacked ribulose bisphosphate carboxylase and did not fix carbon dioxide autotrophically. It also lacked ribulose-monophosph ate-dependent hexulose phosphate synthase. Growth on methanol, methyla mmonium and other C-1 compounds was exhibited, but ability to oxidize MSA was not induced by growth on these substrates. Similarly, methylam monium (MMA) was only oxidized by strain M2 grown on MMA. Growth on me thanol involved a pyrroloquinoline quinone (PQQ)-linked methanol dehyd rogenase (large subunit molecular mass 60 kDa). This organism is the f irst methylotroph shown to have the ability to oxidize MSA, by virtue of a novel monooxygenase, and is significant in the global sulphur cyc le as MSA can be a major product of the oxidation in the atmosphere of dimethyl sulphide, the principal biogeochemical sulphur gas.