Biogeochemical cycling of sulfur; thiols in coastal marine sediments

Mopper, Kenneth; Taylor, Barrie

Thiols are major intermediates in the microbial cycling of sulfur and, because of their high reactivity, they may also play important roles in geochemical processes. Preliminary studies using a new, highly sensitive HPLC assay revealed that thiols are present at concentrations up to lOOJlM in intertidal marine sediments from Biscayne Bay (FL). Methanethiol (MeS) and 3-mercaptopropionate (MP) were the major thiols found. The presence of the latter compound suggests that, in addition to protein degradation, anaerobic decomposition of dimethylpropiothetin (DMPT), a major sulfur compound of marine algae and higher plants, may be an important source of thiols and a significant degradation pathway for DMPT in the environment. Acrylic acid produced from this pathway readily adds HS across the double bond, via Michael addition, to form 3-mercaptopropionate. Alternatively, this thiol may be formed directly from DMPT by successive anaerobic demethylations; however the biochemical feasibility of this pathway is presently not known. Addition of a specific disulfide cleaving reagent to sediments revealed that thiols are dominantly present in bound forms. Binding of thiols to sediment particles may be an important mechanism for the incorporation of organic sulfur into geopolymers.