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 the euphotic zone of the ocean. DMSP is degraded through complex interactions within the food web and studies of its dynamics may lead to greater understanding of microbial ecology and food web interactions. In this study we examined the degradation of dissolved DMSP [DMSP(d)] in coastal water samples and tested glycine betaine (GET), a structural analog of DMSP, as a potential inhibitor of this important biogeochemical 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 added DMSP(d). The production of dimethyl sulfide (DMS) from DMSP(d) was also inhibited by GET, but was slightly less sensitive than overall DMSP degradation. The inhibitory effects of GET were short-lived, lasting only 5 to 6 h, after which time net DMSP(d) consumption resumed. Several analogs of GET were also found to be inhibitory to DMSP(d) degradation but unrelated compounds had no effects. Consistent with the inhibitory effects of GET, we found that endogenous DMSP(d) concentrations increased at steady rates in response to GET additions. These GET-induced accumulation rates ranged from 4 to 28 nM d(-1) in water samples collected over the course of a year and may represent the natural turnover rates of DMSP(d). We found no significant effects of GET on particulate DMSP concentrations in natural water samples or in an axenic culture of the prasinophyte Tetraselmis subcordiformis. However, addition 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 inhibitor of DMSP(d) degradation (and DMS production) under some circumstances. However, the short-lived inhibitory effects of GET and the potential for it to cause some direct release from the particulate DMSP pool may limit its application.