Abstract:

Methanogens are a group of anaerobic microorganisms, of the domain archaea, that produce methane as a byproduct of metabolism. Most methanogens reduce carbon dioxide to produce methane, but a small subset utilize other substrates for methane production. Methanosarcina sp. strain MTP4, a methanogen originally isolated from a salt marsh, utlizes methanol, monomethylamine, dimethylamine, and trimethalamine as well as the volatile methylated sulfur compounds methanethiol (MT) and dimethylsulfide (DMS). With MT and DMS consumption, hydrogen sulfide, methane and carbon dioxide are produced. In this study, closed system incubations of the methanogen Methanosarcina sp. strain MTP4 were conducted to quantify the stable sulfur (32S/34S) isotope fractionation during DMS consumption. Calculations show a sulfur isotope fractionation factor (epsilon) of -8 per mil between the sulfur in DMS and the resulting hydrogen sulfide. The methanogens preferentially utilized DMS with the lighter sulfur isotope, thereby enriching unutilized DMS and depleting hydrogen sulfide. These results provide further data that can be used to understand the biogeochemistry of sulfur and methane in anoxic environments.