Microbial consumption of dimethyl sulfide and methanethiol in coastal marine sediments

Abstract

Samples were taken from oxic and anoxic zones of three ecosystems: a cyanobacterial mat, a diatom film and a carbonate sediment. Dimethylsulfide (DMS) concentrations were determined by headspace analysis of sediment slurries: maximal amounts were in the upper 5-10 mm of the sediments of 20 /_LM (cyanobacterial mat), 8 PM (diatom film) and < I PM in the carbonate sediment. Dissolved DMS in the cyanobacterial mat, determined by centrifugation and cryogenic trapping, was about two orders of magnitude lower than from slurry estimations but its variation with depth was similar. CH,SH concentrations in slurried samples, determined after treatment with tributylphosphine, ranged from 2 to 7 PM in the diatom mat and was below the limit of detection (< 0. I PM) in the carbonate sediment. MPN counts of bacteria that grew on DMS under oxic and anoxic (nitrate added) conditions were determined at all three sites. Aerobic DMS utilizers peaked in the surface and decreased with depth, while the population of anaerobic DMS utilizers was relatively constant in the top 20 mm. Populations of DMS utilizers were highest in the cyanobacterial mat and lowest in the carbonate sediment. MPN's of thiosulfate utilizers, aerobic and anaerobic (nitrate added) were determined in the cyanobactetial mat. Populations of aerobic and anaerobic S,O:-utilizers were similar throughout the top 20 mm and comparable to those of DMS utilizers in the top 5 mm, but higher by about IOO-fold below that zone. DMS and CH,SH consumption rates were measured in slurries of sediments and aerobic rates were similar or only slightly higher than anaerobic rates; the latter were stimulated by nitrate.