A multidisciplinary study of DMSP production and lysis - from enzymes to organisms to process modelling.

A billion tonnes of the compatible solute dimethylsulfoniopropionate (DMSP) is made each year by marine phytoplankton, seaweeds, corals, coastal plants and, as shown by us, marine bacteria. DMSP has key roles in marine ecosystems when released into the environment, serving as an osmoprotectant and key nutrient for marine microbial communities. DMSP is also the main precursor of the climate-cooling gas dimethylsulfide (DMS). Many organisms cleave DMSP, producing ~300 million tonnes of DMS annually, ~10 % of which is released into the air. DMS oxidises in the atmosphere, producing aerosols that can lead to increased cloud cover and potential effects on climate, or be returned to land in rain, a key step in the global sulfur cycle. DMSP and DMS are also chemoattractants for many organisms which associate them with food.

Despite the importance of DMSP, knowledge of how and why it is produced is quite superficial. We know that DMSP and DMS production is highly variable between and within the different groups of producers, but the reasons for this variability are not understood, mainly because genes encoding DMSP synthesis enzymes have yet to be identified and DMSP lyases have only just been identified in a DMSP-producing organism.

Our preliminary work has identified dsy genes which encode key DMSP synthesis enzymes in bacteria, diatoms, dinoflagellates, corals and haptophytes - the major groups of marine DMSP-producers. Variability in DMSP/DMS production may stem from their different Dsy enzymes.

Our aim is to establish "why some organisms make more DMSP than others and the contribution of different organisms to global DMSP and DMS production".

It is possible that variability in DMSP production in different organisms stems from the differing efficiencies or expression of their Dsy enzymes. To test this, we will use biochemical techniques to characterise the different Dsy enzymes of the major classes of DMSP-producers.

We will study how diverse, model DMSP-producers express their DMSP and DMS synthesis enzymes in response to varying conditions, since the expression level may govern the amount of DMSP produced. This may shed light on the effects of climate change, e.g., if Dsy and DMSP lyase expression is increased by higher temperatures. For the important DMSP/DMS-producing algae Emiliania huxleyi and Symbiodinium, we will precisely locate the Dsy enzymes within the cell as this will help in understanding the role(s) of DMSP in these organisms. By relating cellular location and Dsy enzymology data to DMSP (and synthesis intermediates) and DMS concentrations, production rates in key DMSP producers and the conditions that enhance accumulation, we will more fully understand why high variability in DMSP and DMS production exists.

As future changes in environmental conditions will likely affect DMSP/DMS production, and potentially climate, and vice versa, it is important to understand and predict these effects. Current estimates of DMSP/DMS production are likely inaccurate due to a lack of integrated studies combining molecular, biogeochemical, process and modelling data. Here, we will carry out a detailed, year-long study at the coastal site L4 in the English Channel (chosen for its location and range of contextual data). We will study the diversity and expression of key genes in DMSP/DMS synthesis, DMSP synthesis rates, group-specific phytoplankton DMSP production, bulk standing stocks of DMSP (and synthesis intermediates) and DMS and microbial diversity over a seasonal succession. Our studies will tell us which organisms produce DMSP/DMS, production rates and concentrations, the genes used and under what conditions. Using these data, we will input critical state and rate parameters into a new model for DMSP/DMS dynamics, allowing the contribution of different taxa to global production of DMSP/DMS to be more accurately predicted, along with any possible effects of climate change.

We show for the first time that marine bacteria can produce dimethylsulfoniopropionate (DMSP), and identify the key gene in DMSP synthesis in these bacteria and all the major classes of DMSP-producing algae. Many of these microbes also lyse DMSP, making the climate-active gas dimethylsulfide (DMS). Our work is important because DMSP/DMS are made in large amounts globally and have key roles in sulfur and nutrient cycling, signalling pathways and climate. The proposed project is driven by the need for a mechanistic understanding of these pathways, the biodiversity of microbes carrying out these processes and environmental stimuli that regulate DMSP/DMS production. Our work will provide essential data for future modelling of DMSP/DMS production in marine environments.

Our work will be of interest to scientists including microbiologists, molecular ecologists, computational biologists, biological modellers and biochemists due to the range of data generated. The resources generated from the English Channel will be invaluable and complement existing biological knowledge of important ecosystems.

DMSP/DMS research is well-represented in recent high impact journals and has been a well-funded and publicised area of NERC research, e.g. a special report on microbial DMS production in Planet Earth (2009). Here the editor highlighted the phrase "It is astonishing that we still do not know of a single gene for DMSP synthesis", emphasising the potential impact of our work. Thus, we are confident our project will be of interest to a wide scientific audience. We will disseminate our findings in the best international peer-reviewed journals and strive to include other publications in journals that have wider audiences, e.g. Microbiology Today.

There is evidence that the media/general public found our previous NERC-funded work into DMSP/DMS to be interesting e.g. the Todd et al (2007) Science paper led to appearances on TV, radio interviews and press reports throughout the world. We will continue to disseminate our findings to the public and media through e.g. UEA, PML, our websites, Twitter and NERC.

Our outreach component of Pathways to Impact focuses on delivering its outcomes mainly to our younger generation. This will be done through SAW (Science Art Writing) and Research Network events (ResNet), and will involve local schools. We will host students in our labs and continue our outreach work to students around Devon and East Anglia via visits, talks and student projects. The posting of material outlining our work on our websites and Twitter will allow us to reach a wider audience.

There are potential commercial and policy outputs from our work. DMSP/DMS research has applications of interest to industry. The co-products of DMSP lyase enzymes, hydroxypropionate or acrylate are high-value chemicals, e.g. in the plastics industry. Also, DMSP is an antistress compound and osmolyte in environments with high salt/sulfur levels, and DMS is a desirable flavour in e.g. beer, wine or other foodstuffs. The ability of the organisms to produce both DMSP/DMS without expensive feedstock addition clearly offers potential benefits to industry. Knowing factors controlling DMSP/DMS production in different producers may allow for optimisation of the processes. The use of genetics and metabolic engineering could be used to improve yield and efficiency and/or introduce pathways into other organisms, e.g. one could potentially engineer methanogenic bacteria or crops to produce these products. As part of our impact plan, we will explore the potential of these ideas through interactions with chemists and industry.

This research will benefit wider society through improvements in policy facilitated by our new model for DMSP/DMS dynamics and its feeding into the European Regional Seas Ecosystem Model (ERSEM). These models can inform policymakers on the potential environmental consequences of changes in DMSP/DMS production under future climate scenarios.