Characterisation of microorganisms driving aerobic DMS degradation in terrestrial and riverine environments

Dimethylsulfide (DMS), a volatile organosulfur compound relevant for atmospheric, biogeochemical, and industrial processes (Schäfer et al., 2010), plays a significant role in transferring sulfur to the atmosphere (Lana et al., 2011). Approximately 80% of DMS emissions to the atmosphere originate from marine environments, the other 20% is attributable to saltmarshes, wetlands, and estuaries; soils and vegetation; and anthropogenic industrial sources (Watts, 2000).

DMS contributes to climate regulation as its aerosol oxidation products serve as cloud condensation nuclei. These increase the albedo effect in the atmosphere, reflecting a higher proportion of the solar radiation that would otherwise reach the Earth's surface (Charlson et al., 1987).

Although DMS has primarily been associated with the marine sulfur cycle, it is also metabolised by diverse non-marine organisms which contribute to an active DMS sink in soils and freshwater sediments, environments where DMS is known to be produced by different biological processes (Lomans et al., 2002, Schäfer et al., 2010). However, our understanding of the non-marine microbial DMS cycle is incomplete and the key microbial players remain poorly characterised.

Previous cultivation-independent work on DMS-degrading communities from one terrestrial (soil) and one freshwater environment suggested that members of Methylophilales may be a dominant clade of DMS degraders despite no DMS-degrading Methylophilales being shown previously (Eyice et al., 2015). Preliminary analysis by us corroborates the potential for DMS metabolism in members of this clade available now, based on the presence in their genomes of mtoX, the gene encoding the methanethiol (MT) oxidase, which degrades MT (Eyice et al., 2018), a key intermediate of DMS metabolism in methylotrophic DMS degraders.

Furthermore, these strains contain genes of oxidation of sulfide and thiosulfate as well as the functions required for methylotrophic assimilation of formaldehyde.

The goal of this project is to gain a better understanding of aerobic DMS degradation in terrestrial and freshwater environments. This will include characterisation of DMS metabolism in the Methylophilales using Methyloversatilis discipulorum as a model organism, and to characterise the contribution of these and other organisms to DMS cycling in terrestrial and freshwater environments using cultivation independent approaches.