| dc.description.abstract | Dimethylsulfide (DMS) is the most abundant biogenic organosulfur compound emitted into the atmosphere. In anoxic sediments, DMS degradation leads to methane, a potent greenhouse gas. Alongside methanogens, sulfate-reducing bacteria (SRB) also degrade DMS, depending on sulfate availability. However, little is known about DMS degradation in anoxic sediments. This PhD aimed to explore the potential for DMS-dependent methane production and the diversity and metabolism of DMS-degrading microorganisms in anoxic sediments. Sediment was sampled along the salinity gradient of the Medway Estuary to understand how sulfate concentrations affect DMS-dependent methanogenesis. Sediment was also collected from rivers, important contributors to the global methane budget. Furthermore, we studied DMS degradation in the Baltic Sea following a phytoplankton bloom, which releases dimethylsulfoniopropionate, a major DMS precursor. The sediment samples were incubated with DMS as the only carbon and energy source. The methanogen and SRB diversities were analysed using taxonomic (16S rRNA) and functional genes (mcrA, dsrB). Samples from the Baltic Sea incubations were also selected for metagenomics and metatranscriptomics analyses. Results showed a 39%-92% methane yield from DMS in all sediment samples, indicating a high potential for DMS-dependent methanogenesis in anoxic sediments regardless of sulfate availability. Methanomethylovorans, Methanococcoides and Methanolobus were the most dominant DMS-degrading methanogens depending on sediment salinity, implying niche-partitioning likely driven by sulfate concentrations. In addition, DMS degradation initiated sulfate recycling in all low-sulfate incubations, thus affecting the sulfur cycle. Lastly, metagenomics and metatranscriptomics analyses showed for the first time that DMS could be degraded via the activity of trimethylamine and methanol methyltransferases rather than previously characterised DMS methyltransferases. This PhD project is the first cultivation-independent study of DMS-degrading microorganisms in anoxic sediments. It highlights the significance of anaerobic DMS degradation for global methane production and the carbon and sulfur cycles. | en_US |
