Dimethyl Sulphoxide and Dimethyl Sulphide as a Carbon, Sulphur and Energy Source for Growth of Hyphomicrobium S

Abstract

A Hyphomicrobium sp. capable of growth on dimethyl sulphide and dimethyl sulphoxide was isolated from aerobic enrichment cultures containing dimethyl sulphoxide as the carbon and energy source. Suspensions of cells taken from a dimethyl sulphoxide-limited chemostat oxidized dimethyl sulphide, methanethiol, formaldehyde, formate and thiosulphate. Enzyme studies indicated that the pathway of dimethyl sulphoxide metabolism involves an initial reduction to dimethyl sulphide, which is subsequently oxidized by an NADH-dependent mono-oxygenase to formaldehyde and methanethiol. Further oxidation of methanethiol is by a hydrogen peroxide-producing oxidase, again resulting in the production of formaldehyde. Extracts of dimethyl sulphoxide-grown cells also contained high levels of catalase as well as NAD+-dependent formaldehyde and formate dehydrogenases. The organism probably used the serine pathway for growth on dimethyl sulphoxide. This was indicated by the presence of high activities of hydroxypyruvate reductase in dimethyl sulphoxide-grown cells.