Distribution of 3-mercaptopropionate in salt-marsh sediments from Shelter Island, New York
- Brookhaven National Lab., Upton, NY (United States)
3-Mercaptopropionate (3-MPA) is a major hydrophilic thiol in salt-marsh sediments. Both biological and chemical mechanisms are possible for forming 3-MPA from {beta}-dimethylsulfonium propionate (DMSP) which occurs at significant levels in the salt-marsh plant Spartina alterniflora. In the biological pathway, sedimentary bacteria demethylates DMSP sequentially, forming first 3-methylthiopropionate, and then 3-MPA. The chemical pathway involves the cleavage of DMSP to form acrylate which then reacts with bisulfide and polysulfide ions to form respectively 3-MPA and 3-polysulfido propionate (3-PPA), the polysulfide derivative. The biological pathway probably dominates in the bulk anoxic sediment, although the chemical pathway is likely to be more important near the sediment-water interface where the cleavage of DMSP to form acrylate can be facilitated by enzymes from the plant tissues. Our results show that bulk of the 3-MPA is bound to the sedimentary solid phase, and can be released as free thiol upon treating with a di- and polysulfide cleavage reagent, tributylphosphine. The particle-bound 3-MPA can be formed either by condensation reactions of 3-MPA with sulfhydryl groups of humic polymers or by addition reaction between acrylate and particle-bound polysulfides. As free thiol, 3-MPA is attacked relatively rapidly by anaerobic bacteria, with degradation following first-order kinetics. However, the distribution of particle-bound 3-MPA throughout the sedimentary column, down to about 25 cm sampled, suggests that the thiol is somewhat resistant to microbial degradation when bound to the sedimentary solid phase. The sedimentary distribution of 3-MPA presents an important illustration of the interplay of biological and chemical processes in the transformations of organic molecules in anoxic marine sediments.
- OSTI ID:
- 370458
- Report Number(s):
- CONF-960376--
- Country of Publication:
- United States
- Language:
- English
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