Breakdown of dimethyl sulphide by mixed cultures and byThiobacillus thioparus

Dimethyl sulphide (DMS) was degraded by acclimatized activated sludge and by a mixed culture of Thiobacillus thioparus TK-1 and Pseudomonas sp. AK-2. While both these organisms persisted in stable co-culture on DMS, it was found that T. thioparus TK-1 and the derived strain TK-m grew in pure culture on DMS, and oxidized DMS with an apparent Km of 4.5 × 10−5 M. During growth, all the DMS-sulphur was oxidized stoichiometrically to sulphate but no methanol was detected in pure cultures of TK-m. DMS-carbon was probably converted to CO2, since the fixation of 14CO2 was progressively diluted during growth of a culture on 14CO2 and DMS. Growth yields were consistent with autotrophic growth, dependent on the oxidation of the methyl residues to CO2 (probably with formaldehyde as a first intermediate) and the sulphide to sulphate. The organism thus appears to exhibit a mixture, from the one substrate, of chemolithotrophic and methylotrophic energy generation supporting autotrophic growth with CO2 fixation.