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Dimethyl sulfoxide (DMSO) is a major waste product from paper mills and is produced in nature in large amounts by biological and chemical oxidation of dimethyl sulfide. These two Hyphomicrobium species can grow aerobically with DMSO as sole source of carbon, energy, and sulfur. The first step in the pathway can also occur in many anaerobic and facultatively anaerobic bacteria, which use DMSO as electron acceptor for anaerobic respiration, releasing dimethyl sulfide. Dimethyl sulfide is the major volatile sulfur compound released from the oceans, where it is derived from dimethylsulfaniopropionate. Dimethyl sulfide can also be produced in terrestrial ecosystems by this pathway. The first two steps in the DMSO biodegradation pathway use NADH for reducing power. Formaldehyde can be oxidized to CO2 to regenerate NADH.
Hydrogen sulfide is a byproduct of anaerobic bacterial respiration with sulfate as electron acceptor. It can be metabolized "back" to dimethyl sulfide by the enzyme thiol S-methyl transferase.
This is the first pathway in the EAWAG-BBD which demonstrates a metabolic cycle (in this case, for organosulfide). For other organosulfide metabolisms, see thiocyanate pathway.
The following is a text-format DMSO and sulfur cycle pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (7k) format.
Dimethyl sulfoxide Hyphomicrobium sp. S Hyphomicrobium sp. EG Rhodobacter sphaeroides | | dimethyl sulfoxide | reductase v Dimethyl sulfide ^ \ / \ / \ thiol S-methyl | | dimethyl sulfide transferase | | monooxygenase | v Methanethiol Methanethiol + Formaldehyde ^ | thiol S-methyl | | methyl mercaptan transferase | | oxidase \ / \ / \ v to the Hydrogen sulfide + Formaldehyde------>C1 Metabolic Cycle Pseudomonas sp. and others
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