Metabolic Pathways Involved in DMSP Degradation

Abstract

Dimethylsulfoniopropionate (DMSP) is initially biodegraded by cleavage into dimethyl sulfide (DMS) and acrylate or by demethylation to 3-methylmercaptopropionate (MMPA). Demethylation of MMPA produces 3-mercaptopropionate (MPA) which is catabolized with the elimination of H2S to leave acrylate. MMPA is also metabolized with the formation of methanethiol by unknown mechanisms. DMSP lyases which catalyze the cleavage of DMSP into DMS and acrylate, occur in a variety of organisms; aerobic and anaerobic bacteria, phytoplankton, macroalgae and possibly higher plants. Biochemical properties reveal the occurrence of more than one DMSP lyase probably because of the different physiological functions of the enzyme. Demethylations of DMSP to MMPA and thence to MPA are performed by aerobic and anaerobic bacteria. In anaerobes the first demethylation step was documented for a species of Desulfobacterium and the second step from MMPA to MPA was established with species of Methanosarcina. MPA degradation has been observed only with anoxygenic phototrophic bacteria (Rhodopseudomonas sp. strain BB1, Thiocapsa roseopersicina) and occurs with H2S elimination to leave acrylate. DMS and methanethiol are degraded by a variety of aerobes and anaerobes. Strict aerobes may use monooxygenases to oxidize the methyl groups whereas facultative and strict anaerobes probably employ transmethylases and a C1-folate system of oxidation. Methanogens probably funnel methyl groups from DMS, methanethiol and MMPA via specific methyl transferases to methyl coenzyme M reductase.