Biogeochemical cycling of N-osmolytes in the surface ocean

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.

This project addresses fundamental questions relating to the marine biogeochemical cycles and climate-active gas emissions from the natural environment, both of which are crucial to our understanding of global biogeochemical cycles and in the drive for a more sustainable future. The work is therefore of the utmost relevance to NERC's strategic aims, particularly Biodiversity Science and Climate Change themes.

The proposal work relies on the recent development of the two new techniques, i.e. Raman microspectroscopy in combination with stable isotope labelling and liquid chromatography (LC) with electrospray ionization mass spectrometry (LC-ESI-MS) for quantifying N-osmolytes. The proposed work is therefore of direct relevance to the immediate science community and NERC's Technologies theme.

The main beneficiary of the knowledge generated from this study is anticipated to be public sectors focusing on marine ecosystems services and the scientific community working on marine aerosol research and marine microbes. Marine aerosols play an important role in the Earth system, not only in climate, but also in atmospheric chemistry and human health problems. Until recently, sea-salt formation from bubble bursting and dimethylsulfide (DMS) oxidation were thought to be the main sources of marine aerosols. There is growing evidence in the past five years that methylated amines play an important role in marine aerosol formation, in addition to DMS. Methylated amine concentrations measured over the North Atlantic Ocean and the North Pacific Ocean have shown distinct seasonal variation and are directly linked to the primary productivity of phytoplankton. However, researchers working on atmospheric chemistry and modelling have not yet been able to pinpoint the origin of the methylated amines found in the marine atmosphere. There is a lack of communication to such a community which can be catalyzed through the proposed research and subsequent impact plan activities.

Our topic also has immediate general interest for the wider public, including general public, school pupils. With its relevance to climate and marine biology, this type of work is guaranteed to attract considerable attention in the media.