Methanogenic conversion of 3-s-methylmercaptopropionate to 3-mercaptopropionate

Anaerobic metabolism of dimethylsulfoniopropionate, an osmolyte of marine algae, in anoxic intertidal sediments involves either cleavage to dimethylsulfide or demethylation to 3-S-methylmercaptopropionate (MMPA) and subsequently to 3-mercaptopropionate. The methanogenic archaea Methanosarcina sp. strain MTP4 (DSM 6636), Methanosarcina acetivorans DSM 2834, and Methanosarcina (Methanolobus) siciliae DSM 3028 were found to use MMPA as a growth substrate and to convert it stoichiometrically to 3-mercaptopropionate. Approximately 0.75 mol of methane was formed per mol of MMPA degraded; methanethiol was not detected as an intermediate. Eight other methanogenic strains did not carry out this conversion. We also studied the conversion of MMPA in anoxic marine sediment slurries. Addition of MMPA (500 (mu)M) resulted in the production of methanethiol which was subsequently converted to methane (417 (mu)M). In the presence of the antibiotics ampicillin, vancomycin, and kanamycin (20 (mu)g/ml each), 275 (mu)M methane was formed from 380 (mu)M MMPA; no methanethiol was formed during these incubations. Only methanethiol was formed from MMPA when 2-bromoethanesulfonate (25 mM) was added to a sediment suspension. These results indicate that in natural environments MMPA could be directly or indirectly a substrate for methanogenic archaea.