Is bacterial DMS consumption dependent on methylamines in marine waters?

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Dimethylsulfide (DMS) is a key ingredient in the cocktail of gases that makes up the 'smell of the sea'. Around 300 million tons of DMS are formed each year by single-celled organisms in the surface ocean. A small proportion (up to 16%) of this DMS is released into the atmosphere, forming cloud-seeding compounds which can influence our weather and climate. When it rains, sulfur compounds are deposited back into the soils of our continents. However, most of the DMS formed in the oceans stays there, facing consumption by marine microbes and conversion to another sulfur compound - dimethylsulfoxide (DMSO). DMSO is usually the most abundant organic sulfur compound in the oceans and represents a major pool of the essential life elements sulfur and carbon.Seawater contains a rich mixture of important chemical nutrients that support the entire oceanic food web. The dissolved organic nitrogen pool is a chemical 'drive thru' which contains the highly reactive N-osmolytes: glycine betaine, choline and trimethylamine N-oxide. These chemicals are used by microorganisms to protect them from changes in their environmental conditions, such as variability in the saltiness of the surrounding seawater, and to protect their cells from chemical or physical damage. When N-osmolytes breakdown they can release gases such as methylamines into the atmosphere which can influence the climate.We have found a previously unrecognised and intriguing link between the bacterial breakdown of organic nitrogen compounds, like methylamines, and organic sulfur compounds like DMS. This link is provided by a bacterial enzyme called trimethylamine monooxygenase (TMM). TMM simultaneously removes both methylamines and DMS from seawater (converting it to DMSO). In fact this production of DMSO doesn't happen without the presence of methylamines. We estimate that up to 20% of all bacteria in our oceans contain this particular enzyme. The research we want to carry out will firstly investigate this link between DMS removal and methylamine availability in 'model' micro-organisms in the laboratory, checking that this link is active and how it is controlled in key marine bacteria commonly found in the global oceans. We will next determine the importance of this process compared to other biological processes that consume DMS in seawater and put names to the microbes using this enzyme to remove DMS. We will study the microbial processes linking the organic sulfur and nitrogen cycles in the English Channel at a station that is sampled weekly as part of the Western Channel Observatory which is coordinated by Plymouth Marine Laboratory. This is a long-standing time series site for which a wealth of oceanographic and biological data are available (algal diversity, temperature, nutrients etc.; http://www.westernchannelobservatory.org.uk), which we will be able to use. A global model of particles in the atmosphere has recently suggested that changes in the location of DMS emissions, through climate-driven changes in the phytoplankton species distributions, could strongly influence our climate. We therefore want to investigate the link between DMS removal, the availability of organic nitrogen compounds like methylamines and phytoplankton species, which we can do at station L4, where phytoplankton species succession is understood and can be easily sampled.We will compare this temperate coastal region to one of the Earth's DMS hotspots - the Southern Ocean. The atmosphere above this remote and isolated ocean is pristine in comparison to the heavily polluted air of the Northern Hemisphere. Here, the connection between DMS produced in the oceans and our climate is thought to be the strongest. Given the important role of DMS, identifying the role of marine microorganisms and the pathways of DMS removal from seawater will provide key information that will improve our future understanding of how the sulfur cycle influences our climate.