DEMETHYLATION AND CLEAVAGE OF DIMETHYLSULFONIOPROPIONATE IN MARINE INTERTIDAL SEDIMENTS

Demethylation and cleavage of dimethylsulfoniopropionate (DMSP) was me asured in three different types of intertidal marine sediments: a cyan obacterial mat, a diatom-covered tidal flat and a carbonate sediment. Consumption rates of added DMSP were highest in cyanobacterial mat slu rries (59 mu mol DMSP l(-1) slurry h-l) and lower in slurries from a d iatom mat and a carbonate tidal sediment (24 and 9 mu mol DMSP l(-1) h (-1), respectively). Dimethyl sulfide (DMS) and 3-mercaptopropionate ( MPA) were produced simultaneously during DMSP consumption, indicating that cleavage and demethylation occurred at the same time. Viable coun ts of DMSP-utilizing bacteria revealed a population of 2x10(7) cells c m(-3) sediment (90% of these cleaved DMSP to DMS, 10% demethylated DMS P to MPA) in the cyanobacterial mat, 7X10(5) cells cm(-3) in the diato m mat (23% cleavers, 77% demethylators), and 9x10(4) cells cm(-3) (20% cleavers and 80% demethylators) in the carbonate sediment. In slurrie s of the diatom mat, the rate of MPA production from added 3-methiolpr opionate (MMPA) was 50% of the rate of MPA formation from DMSP. The pr esence of a large population of demethylating bacteria and the product ion of MPA from DMSP suggest that the demethylation pathway, in additi on to cleavage, contributes significantly to DMSP consumption in coast al sediments.