Production and consumption of volatile organosulfur compounds in microbial mats

Abstract

Marine microbial mats typically support high rates of sulfate reduction. As a result, sulfur cycling is one of the dominant biogeochemical processes in these ecosystems. Detailed studies on inorganc sulfur cycling are available, but little is known about organic sulfur transformations. Sulfur-containing amino acids and dimethylsulfoniopropionate (DMSP) are the major biogenic precursors of volatile organosulfur compounds. DMSP, which functions as an osmolyte, is cleaved to acrylate and dimethylsulfide (DMS; White 1982). Production of DMS and methane thiol (CH3SH) from decaying microbial mats in Yellowstone was reported by Zinder et al. (1977). Upon hydrolysis with NaOH, 200 μmol DMS 1-1 sediment was retrieved from intact marsh sediments (Kiene 1988), and DMSP, DMS, CH3SH and dimethyldisulfide (DMDS) were found in slurried samples of a marine microbial mat (Visscher et al. 1991; Visscher and Van Gemerden 1993). Kiene and Visscher (1987) found production of CH3SH from methionine and DMS from DMSP in anoxic salt marsh sediments. Visscher and Van Gemerden (1991b) reported rapid production of DMS, CH4 and traces of CH3SH in oxic and anoxic mat slurries when DMSP was added. In addition to cleavage, DMSP also undergoes demethylation, during which 3-methiolpropionate (MMPA) and 3-mercaptopropionate (MPA) are formed successively (Mopper and Taylor 1986; Kiene and Taylor 1989). MPA was a dominant thiol in anoxic sediments of Biscayne Bay, and DMSP addition resulted in increasing MPA production in slurries (Kiene and Taylor 1989). Sulfur-containing amino acids added to coastal sediments generated a variety of thiols, including CH3SH and MPA (Kiene et al. 1990).