EVALUATION OF GLYCINE BETAINE AS AN INHIBITOR OF DISSOLVED DIMETHYLSULFONIOPROPIONATE DEGRADATION IN COASTAL WATERS

Dimethylsulfoniopropionate (DMSP) is an organic sulfur compound which is produced by many marine phytoplankton and which is ubiquitous in th e euphotic zone of the ocean. DMSP is degraded through complex interac tions within the food web and studies of its dynamics may lead to grea ter understanding of microbial ecology and food web interactions. In t his study we examined the degradation of dissolved DMSP [DMSP(d)] in c oastal water samples and tested glycine betaine (GET), a structural an alog of DMSP, as a potential inhibitor of this important biogeochemica l reaction. The addition of 1 to 50 mu M GET to water samples from the northern Gulf of Mexico strongly inhibited the consumption of 50 nM a dded DMSP(d). The production of dimethyl sulfide (DMS) from DMSP(d) wa s also inhibited by GET, but was slightly less sensitive than overall DMSP degradation. The inhibitory effects of GET were short-lived, last ing only 5 to 6 h, after which time net DMSP(d) consumption resumed. S everal analogs of GET were also found to be inhibitory to DMSP(d) degr adation but unrelated compounds had no effects. Consistent with the in hibitory effects of GET, we found that endogenous DMSP(d) concentratio ns increased at steady rates in response to GET additions. These GET-i nduced accumulation rates ranged from 4 to 28 nM d(-1) in water sample s collected over the course of a year and may represent the natural tu rnover rates of DMSP(d). We found no significant effects of GET on par ticulate DMSP concentrations in natural water samples or in an axenic culture of the prasinophyte Tetraselmis subcordiformis. However, addit ion of 50 mu M GET to the phytoplankton culture caused an accumulation of DMSP(d) (equivalent to 2% of the particulate DMSP in the culture) for a period of 1 h with no change thereafter. GET may be a useful inh ibitor of DMSP(d) degradation (and DMS production) under some circumst ances. However, the short-lived inhibitory effects of GET and the pote ntial for it to cause some direct release from the particulate DMSP po ol may limit its application.