METHANESULFONATE UTILIZATION BY A NOVEL METHYLOTROPHIC BACTERIUM INVOLVES AN UNUSUAL MONOOXYGENASE

Methylotroph strain M2, isolated from soil, was capable of growth on methanesulphonic acid (MSA) as sole carbon and energy source. MSA was oxidized 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 hydroxypyruvate reductase in MSA-grown bacteria indicated the production of formaldehyde from MSA (and its further oxidation for energy generation), and assimilation of formaldehyde by means of the serine pathway. Growth yields 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 either methane or methanol, but appears to be by an NADH-dependent methanesulphonate monooxygenase, cleaving MSA into formaldehyde and sulphite. The organism lacked ribulose bisphosphate carboxylase and did not fix carbon dioxide autotrophically. It also lacked ribulose-monophosphate-dependent hexulose phosphate synthase. Growth on methanol, methylammonium and other C-1 compounds was exhibited, but ability to oxidize MSA was not induced by growth on these substrates. Similarly, methylammonium (MMA) was only oxidized by strain M2 grown on MMA. Growth on methanol involved a pyrroloquinoline quinone (PQQ)-linked methanol dehydrogenase (large subunit molecular mass 60 kDa). This organism is the first methylotroph shown to have the ability to oxidize MSA, by virtue of a novel monooxygenase, and is significant in the global sulphur cycle as MSA can be a major product of the oxidation in the atmosphere of dimethyl sulphide, the principal biogeochemical sulphur gas