MICROBIAL CONSUMPTION OF DIMETHYL SULFIDE AND METHANETHIOL IN COASTALMARINE-SEDIMENTS

Samples were taken from oxic and anoxic zones of three ecosystems: a c yanobacterial mat, a diatom film and a carbonate sediment. Dimethylsul fide (DMS) concentrations were determined by headspace analysis of sed iment slurries; maximal amounts were in the upper 5-10 mm of the sedim ents of 20 mu M (cyanobacterial mat), 8 mu M (diatom film) and < 1 mu M in the carbonate sediment. Dissolved DMS in the cyanobacterial mat, determined by centrifugation and cryogenic trapping, was about two ord ers of magnitude lower than from slurry estimations but its variation with depth was similar. CH3SH concentrations in slurried samples, dete rmined after treatment with tributylphosphine, ran,oed from 2 to 7 mu M in the diatom mat and was below the limit of detection (< 0.1 mu M) in the carbonate sediment. MPN counts of bacteria that grew on DMS und er oxic and anoxic (nitrate added) conditions were determined at all t hree sites, Aerobic DMS utilizers peaked in the surface and decreased with depth, while the population of anaerobic DMS utilizers was relati vely constant in the top 20 mm, Populations of DMS utilizers were high est in the cyanobacterial mat and lowest in the carbonate sediment. MP N's of thiosulfate utilizers, aerobic and anaerobic (nitrate added) we re determined in the cyanobacterial mat. Populations of aerobic and an aerobic S2O32- utilizers were similar throughout the top 20 mm and com parable to those of DMS utilizers in the top 5 mm, but higher by about 100-fold below that zone. DMS and CH3SH consumption rates were measur ed in slurries of sediments and aerobic rates were similar or only sli ghtly higher than anaerobic rates; the latter were stimulated by nitra te.