Biogeochemical cycling of N-osmolytes in the surface ocean

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Nitrogen-containing compounds, including glycine betaine (GBT), choline and trimethylamine N-oxide (TMAO) are ubiquitous in marine organisms. They are used by marine organisms as compatible solute in response to changes in environmental conditions, such as increasing salinity, because they do not interfere with cell metabolisms. They also have beneficial effects in protecting proteins against denaturation due to chemical or physical damages.In the marine environments, these compounds are frequently released into the sea water due to the change of environmental conditions, such as viral attack or grazing. The released nitrogenous osmolytes serve as important nutrients for marine microorganisms, which can use them as carbon, nitrogen and energy sources. It is well known that the degradation of these nitrogenous osmolytes contribute to the release of climate-active gases, including volatile methylated amines. Methylated amines are important sources of aerosols in the marine atmosphere, which help to reflect sunlight and cause a cooling effect of the climate. There is an urgent need to understand the microbial metabolism of these compounds and their seasonal cycles in the marine water column, in order to better understand their role in marine biogeochemical cycles and their role in future climate change.Built on the recent progress on the discovery of the new pathway of TMAO degradation in marine organisms and the development of a powerful liquid chromatography with mass spectrometry (LC-ESI-MS) method for simultaneous quantification of these nitrogenous osmolytes from the applicants' laboratories, this timely proposal aims to determine the seasonal cycle of nitrogenous osmolytes in the surface seawater and to address how these environmentally-relevant compounds are degraded and what are the major microorganisms that are involved in the process. The data generated will fill in a major gap in our knowledge of marine carbon and nitrogen cycles and the contribution of these compounds in future climate change through the release of climate-active molecules. Using newly developed analytic techniques, we aim to determine the seasonal cycle of standing concentrations of nitrogenous osmolytes in the surface seawater and microbial oxidation activities. These data will be incorporated to a biogeochemical model for future prediction of biogeochemical cycles of N-osmolytes under climate change. Using cultivated model organisms, we aim to define the key genes, enzymes and the metabolic pathways in GBT and TMAO degradation by marine planktonic microbes.Using molecular and single cell manipulation techniques, we aim to further determine the key microbial players involved in the metabolism of nitrogenous osmolytes in surface seawater from the English Channel.This work will generate novel knowledge about our understanding of microbial transformation of these nitrogen containing compounds, and will fill in a serious gap in knowledge of marine carbon and nitrogen cycles. The project is expected to further strengthen the UK as a leading country not only in the research of marine biogeochemical cycles and marine microbiology, but also in the development of cutting edge technology in environmental science.