RADIOISOTOPE AND CHEMICAL INHIBITOR MEASUREMENTS OF DIMETHYL SULFIDE CONSUMPTION RATES AND KINETICS IN ESTUARINE WATERS

Microbial consumption rates of 1 to 20 nM dimethyl sulfide (DMS) in es tuarine whole-water samples from coastal Georgia (USA) were measured b y 2 methods: production of radiolabeled CO2 and particulates > 0.2 mum from ((CH3)2S)-C-14, and specific inhibition by addition of 500 muM c hloroform. The combination and comparison of these 2 methods helped ov ercome some inherent limitations of each one, and both methods gave sh ort turnover times (< 1 d) at low DMS concentrations (1 to 3 nM). DMS production was often as rapid as its consumption, suggesting very tigh t cycling. However, when exogenous DMS was added to increase concentra tions, consumption rates saturated below 20 nM, suggesting high affini ties for DMS. Kinetics and rates appeared similar over a several week period in samples taken from the Duplin River, a coastal tidal river w here DMS concentrations were consistently in the range of 1 to 3 nM. I n contrast, samples of water which had recently flooded the marsh had much higher DMS concentrations, but consumption rates were similar to those observed in the creek waters before they flooded the marsh. The turnover times calculated for the waters over the marsh were on the or der of 3 to 7 d. The radioisotope method showed that DMS assimilation into cell material was approximately equal to that respired as CO2, an d confirmed 500 muM CHCl3 as an excellent inhibitor of DMS consumption . However, it appears that chloroform may in some cases increase disso lved DMSP concentrations and hence DMS production, leading to overesti mates of DMS consumption rates, Two other inhibitors of DMS consumptio n, dimethyl disulfide (100 nM) and dimethyl ether (30 muM), gave simil ar but lower consumption rates compared to chloroform, and show promis e as specific inhibitors for future studies.