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The use of dimethylsulfoniopropionate (DMSP) by the anoxygenic phototrophic purple sulfur bacterium Thiocapsa roseopersicina M11 under different environmental conditions was studied. Under anoxic/light conditions DMSP cleavage occurred both at low and intermediate salinities but at different growth phases: at low salinity (5 parts per thousand S) DMSP cleavage was observed in the exponential growth phase, whereas at intermediate salinity (35 parts per thousand S) cleavage was not observed until the stationary phase was reached. At higher salinities DMSP accumulated intracellularly, prior to cleavage, suggesting usage as compatible solute. Circumstantial evidence suggests that under anoxic/light conditions acrylate, one of the DMSP cleavage products, was reduced to propionate at the expense of intracellular sulfur oxidation, and subsequently used as carbon source. The addition of acrylate had an inhibitory effect on growth, the reduction of acrylate to propionate can thus play an additional role as a detoxification mechanism. Dimethyl sulfide (DMS), also a DMSP cleavage product, was not used under anoxic conditions. However, under oxic conditions both DMS and acrylate metabolization resulted in protein production. DMSP lyase in cell suspensions was induced by acrylate and activity was enhanced in the light. The latter suggests that DMSP cleavage is an energy dependent process. The potential anaerobic DMS production and aerobic consumption in T, roseopersicina M11 is in agreement with previously observed diurnal DMS dynamics in coastal marine sediments, the natural habitat of this anoxygenic phototrophic bacterium. This is the first report in which a bacterium is described that is able to cleave DMSP with subsequent metabolization of DMS. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.