NI: Microbial Dimethylsulphide Degradation in Anoxic Baltic Sea Sediments

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Methane is a powerful greenhouse gas which significantly contributes to global warming. This gas is produced by microbes that live in environments that lack oxygen (anoxic). We have known for some time that marine environments produce substantial amounts of methane. However, the sources of methane in marine ecosystems have not been fully described, which is a barrier to correct calculation of methane emissions from these environments. In particular, we know very little about which microbes produce methane and what metabolic process they use.Previous studies showed that microbes can use dimethylsulphide (DMS) to grow and produce methane. DMS is a gas, which can be found in very high concentrations in marine environments. DMS in these habitats is produced through the breakdown of another compound shortly called DMSP, which is released in huge amounts following a phytoplankton bloom. The Baltic Sea is a unique environment. This is because it is one of the largest brackish (moderate to low salinity) seas in the world. It is also subjected to regular phytoplankton blooms. Overall, the Baltic Sea provides an excellent natural laboratory to study DMS use and methane generation by microbes. The brackish condition of the Baltic Sea is particularly important. Because, sulphate is one of the important ions that determine the salinity. Low-to-moderate salinity means there is sulphate available to microbes. This may however affect the activity of methane-producing microbes. This is because methane-producers compete with sulphate-users for carbon sources, in our case for DMS. Depending on the outcome of this interaction, the amount of methane produced in marine sediments may reduce significantly. Therefore, we aim to understand how this metabolic pathway works and which microbes are responsible of this process. In order to achieve our aim, we initiate a new partnership with colleagues from Sweden, who have long-term experience in the Baltic Sea research and tools to analyse critical data using powerful computing facilities. We will use our novel microbial ecology approach that combines state-of-the-art techniques with advanced microbial identification tools called high-throughput sequencing. Firstly, we will determine the extent to which DMS contributes to methane production in anoxic, brackish Baltic Sea sediments. We will then use isotopically labelled DMS, which enables us to follow the fate of carbon in sediments. Then, we will use genetic material (DNA and RNA) from microbes in the labelled sediment samples to identify the microbes that use DMS (methane-producing or sulphate-using) and infer their metabolism. The results will tell us the magnitude of methane production via DMS, which microbes use DMS and produce methane and how they carry out this process in brackish conditions in the Baltic Sea sediments. Overall, the outcome of this project will greatly improve our understanding of methane production in marine sediments and help in calculating greenhouse gas budgets via improved climate models. This will ultimately help us tackling global warming and climate change.