Microbial Cycling of DMSP and DMS in Coastal and Oligotrophic Seawater

The rates and concentration dependence of microbial dimethysulfide (DMS) and dimethylsulfoniopropionate (DMSP) cycling were assessed in Vineyard Sound, Massachusetts, and the Sargasso Sea. Net rates of dissolved DMSP loss, DMS production from DMSP, and DMS consumption were measured at ambient and near-ambient substrate levels. Turnover times of dissolved DMSP, based on loss rates, were short, usually ranging from 1.5 d to several hours. However, the specific process of DMSP cleavage to form DMS accounted for only a protion of total DMSP turnover. Short-term variability obscured possible regional or seasonal trends in the data. Dissolved DMSP removal and cleavage exhibited saturable kinetics in spring in Vineyard Sound and in winter in the Sargasso Sea. In fall and spring in ths Sargasso Sea, where dissolved DMSP levels ranged from 2 to 9 nM, DMSP cleavage did not saturate at DMSP levels as high as 1$\muM$. Kinetic parameters of DMSP uptake appeared to increase with proximity to summer, as did the proportion of DMSP uptake resulting in DMS production.