Dr Joanna Dixon, a Senior Biogeochemist at PML, is leading a team to investigate an intriguing link between the bacterial breakdown of organic sulfur compounds and organic nitrogen compounds, focusing on a bacterial enzyme called trimethylamine monooxygenase (TMM).
TMM removes dimethylsulfide (DMS) from the water, converting it to dimethylsulfoxide (DMSO). DMS is a chemical compound, formed in large quantities by single-celled organisms in the surface ocean, that contributes to the distinctive 'smell of the sea'. Some DMS enters the atmosphere, becoming cloud-seeding compounds that influence weather and climate, but most stays in the sea. Here, it is converted to DMSO, which is usually the most abundant sulfur compound in the ocean and major source of essential life elements, sulfur and oxygen.
TMM also removes methylamines from the sea, compounds which form from the breakdown of highly reactive organic nitrogen compounds, N-osmolytes. The N-osmolytes are used by microorganisms to protect themselves from changes in their environment such as salt levels, and from chemical and physical damage.
It is suspected that TMM's conversion of DMS to DMSO can only happen in the presence of the methylamines, and Dr Dixon's team will be testing this on board by sampling seawater and performing experiments with and without added methylamines. With up to 20% of all ocean bacteria estimated to contain this particular enzyme, the process being studied is likely to be relevant not just in the Arctic, but across the world's oceans.
Dr Dixon said: “I feel extremely privileged to have the opportunity to undertake our cutting edge science in the fragile and rapidly-changing Arctic ecosystem. 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. It is important therefore that we investigate the link between DMS removal and the availability of organic nitrogen compounds like methylamines in this poorly understood part of the DMS system. 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.”
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