Sediment from a microbial mat from the South‐West coast of the Netherlands consumed dimethylsulfide (DMS) under oxic and anoxic conditions. From this sediment, a Gram‐negative, oval DMS oxidizing bacterium, strain RB‐1, was isolated. Its substrate range is typical of an obligately methylotrophic organism. Enzyme analysis revealed the presence of the ribulose monophosphate pathway for carbon assimilation, and the ability to use the linear dissimilatory pathway via formate to carbon dioxide, as well as the cyclic pathway via the ribulose monophosphate route for carbon dissimilation. 16S rRNA sequence analysis showed high similarity with species belonging to the genus Methylophaga. Because of the specific dimethylsulfide and hydrogen sulfide oxidizing capacity, the new isolate was named Methylophaga sulfidovorans.

C1 organic sulfides are part of many ecosystems and play an important role in the global sulfur budget and climate regulation. At this point, fluxes and conversions of these compounds are only superficially understood. Understanding of the regulating mechanisms will be necessary to quantify the role of these compounds in the global sulfur budget at their climatic role. In this review, the current knowledge of fluxes and conversions of C1 organic sulfides in different ecosystems is presented.

Pure and mixed cultures of Methylophaga sulfidovorans and Thiobacillus thioparus T5 were grown in continuous cultures on either dimethyl sulfide, dimethyl sulfide and H 2 S, or H 2 S and methanol. In pure cultures, M. sulfidovorans showed a lower affinity for sulfide than T. thioparus T5. Mixed cultures, grown on dimethyl sulfide, showed coexistence of both species. M. sulfidovorans fully converted dimethyl sulfide to thiosulfate, which was subsequently further oxidized to sulfate by T. thioparus T5. Mixed cultures supplied with sulfide and methanol showed that nearly all the sulfide was used by T. thioparus T5, as expected on the basis of the affinities for sulfide. The sulfide in mixed cultures supplied with dimethyl sulfide and H 2 S, however, was used by both bacteria. This result may be explained by the fact that the H 2 S-oxidizing capacity of M. sulfidovorans remains fully induced by intracellular H 2 S originating from dimethyl sulfide metabolism.

Methylophaga sulfidovorans is an obligately methylotrophic, DMS‐oxidizing organism, isolated from microbial mat sediment. DMS and H2S, both present in marine microbial mats, can be used as energy sources by this organism. In batch cultures of M. sulfidovorans, sequential H2S and DMS utilization occurred. In energy‐limited continuous cultures, with DMS, methanol and H2S as substrates, mixotrophic growth of M. sulfidovorans was observed, showing that at low concentrations these substrates can be used simultaneously. Oxygen and H2S uptake experiments showed that the critical concentration at which sulfide inhibition of DMS oxidation occurred was between 15 and 40 μmol l−1. Also in crude enrichments of DMS oxidizers a decrease of 50% in DMS‐oxidizing capacity for about 200 μmol l−1 H2S was observed. The new physiological data obtained with the pure cultures of M. sulfidovorans were incorporated in a compartment model of a microbial mat and gave improved predictions of DMS profiles and DMS emissions from the mat, both when phototrophic activity is present (day) and when it is absent (night).

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A model has been developed to describe the biological conversions of five functional groups of microorganisms in a microbial mat. Microbial metabolism and transport of nutrients are the two dominant processes that were considered. The microbial activity was described with Michaelis‐Menten kinetics. Transport of nutrients through the mat was described by simple transport processes. The model was validated using documented measurements, and was used to simulate the fluxes of compounds and concentrations in a microbial mat during a light period of 12 hours. Experimental data from Methylopila sulfovorans cultures (isolated from a microbial mat) were incorporated in the model in order to describe DMS oxidation under varying conditions in a mat.