Dynamics of dimethyl sulfide in a marine microbial mat

The microbial mat was chosen as a model ecosystem to study dynamics of dimethyl sulfide (DMS) in marine sediments in order to gain insight into key processes and factors which determine emission rates. A practical advantage, compared to open ocean ecosystems, is that microbial mats contain high biomasses of different functional groups of bacteria involved in DMS dynamics, and that DMS concentrations are generally high enough to allow direct measurement of emission rates. Field data showed that, during the seasonal development of microbial mats, concentrations of chlorophyll a corresponded to dimethylsulfoniopropionate (DMSP). DMSP is an important precursor of DMS. It was demonstrated, with laboratory cultures, that various species of benthic diatoms produce substantial amounts of DMSP. The abundances of aerobic and anaerobic DMS or DMSO-utilizing bacteria were estimated using the most-probable-number technique. Laboratory experiments with relatively undisturbed sediment cores showed that microbial mats act as a sink for DMS under oxic/light (day) conditions, and as a source of DMS under anoxic/dark (night) conditions. Axenic culture studies with Chromatium vinosum M2 and Thiocapsa pfennigii M8 (isolated from a microbial mat) showed that, under anoxic/light conditions, DMS was quantitatively converted to dimethylsulfoxide (DMSO). T. roseopersicina M11 converted DMSP to DMS and acrylate, apparently without use of either substrate.