METHANOGENIC CONVERSION OF 3-S-METHYLMERCAPTOPROPIONATE TO 3-MERCAPTOPROPIONATE

Anaerobic metabolism of dimethylsulfoniopropionate, an osmolyte of mar ine 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 M ethanosarcina sp. strain MTP4 (DSM 6636), Methanosarcina acetivorans D SM 2834, and Methanosarcina (Methanolobus) siciliae DSM 3028 were foun d to use MMPA as a growth substrate and to convert it stoichiometrical ly to 3-mercaptopropionate. Approximately 0.75 mol of methane was form ed per mol of MMPA degraded; methanethiol was not detected as an inter mediate. Eight other methanogenic strains did not carry out this conve rsion. We also studied the conversion of MMPA in anoxic marine sedimen t slurries. Addition of MMPA (500 mu M) resulted in the production of methanethiol which was subsequently converted to methane (417 mu M). I n the presence of the antibiotics ampicillin, vancomycin, and kanamyci n (20 mu g/ml each), 275 mu M methane was formed from 380 mu M MMPA; n o 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 environm ents MMPA could be directly or indirectly a substrate for methanogenic archaea.