My recent research has resulted in the exciting discovery of a sulphate-reducing bacterium (SRB) from the human gut, Desulfovibrio diazotrophicus, which fixes nitrogen in vitro. While nitrogen-fixing bacteria have been found in the gut microbiomes of some animals, such as termites and ruminants, little is known about the process of nitrogen fixation in humans. Demonstrating that nitrogen fixation occurs in the human gut microbiome would represent a significant scientific finding and expand our understanding of the nitrogen cycle and microbial interactions within the human body. This research, therefore, has implications for human health and nutrition as well as the role of the microbiome. The composition and activity of bacterial populations in the gut are influenced by the host's diet, particularly the availability of nutrients. Investigating bacterial populations in response to different nitrogen levels and availability in the diet provides an opportunity to explore whether nitrogen fixation is influenced by our food intake. This research aims to determine whether diazotrophic (N-fixing) bacteria have a competitive advantage in the human gut when low-protein diets are consumed. My metagenomics analyses found that while SRB are frequently present in human gut microbiomes, not all species have the potential to fix nitrogen. Some SRB species could contribute to the bioavailable nitrogen in protein-deficient diets; however, blooms of SRB have been linked with colonic diseases, gut inflammation, and ulcerative colitis. The by-product of SRB respiration, H2S, is toxic in high concentrations but can also be anti-inflammatory. Therefore, this project will provide a better understanding of SRB ecology and metabolism in the gut, which is crucial to understanding whether they are beneficial or potentially harmful to health. I aim to investigate the impact of nitrogen fixation on D. diazotrophicus survival and metabolism, the effects nitrogen fixation has on the microbiota and the host, and how diet influences these interactions. The hypotheses are that sulphate-reducing bacteria can fix nitrogen under gastrointestinal conditions, and this process is influenced by the quantity and source of dietary protein, subsequently affecting H2S production. Additionally, it is hypothesized that fixed nitrogen is shared with the rest of the microbiota or utilized by the host. The specific objectives are: Investigate the rate of nitrogen fixation by D. diazotrophicus in the gut environment, if this nitrogen is shared, and assess the extent to which this process is influenced by dietary protein content Determine the influence of vegan diets on nitrogen fixation by D. diazotrophicus and identify key interactions within a complex microbiota Evaluate the impact of D. diazotrophicus on the host's nitrogen pool and gut permeability Implications My discovery of nitrogen-fixing SRB in the human gut has the potential to revolutionize our understanding of the complex interactions between human nutrition, the microbiome and health. Protein-deficient diets cause malnutrition and can be severe for vulnerable populations, as the elderly and pregnant women. The outcomes will inform new nutritional strategies that could address protein deficiency in vegan diets, the elderly and the malnourished.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

The Arctic is a considerable organic carbon store (~1672 Pg) and the terrestrial and aquatic processing of this C pool is essentially mediated by microorganisms. Understanding the mechanisms regulating the diversity and structure of functionally-important microbial communities is urgently required for predicting the ecological impacts of rapidly changing environments, such as a warming Arctic. All aquatic ecosystems (lakes, rivers, the oceans) contain very substantial amounts of dissolved organic matter (DOM). The amount of DOM can exceed the amount of carbon contained in living organisms (plants, animals, microbes, etc.). This accumulated organic matter is the product of photosynthesis, consumption and degradation pathways, and can contain a range of material, from compounds that are 100's of years old, and are difficult for bacteria to break down, to recently produced organic matter that may have leaked from living algal cells as they photosynthesise, which can quickly be used by bacteria and other microorganisms. This microbial action generates food for other organisms, and promotes nutrient regeneration, and recycles the organic matter back into food chains. Other DOM can stick together and become buried in sediments and locked away for geological periods of time. The huge quantities of DOM present in aquatic systems mean that understanding its characteristics and dynamics (biogeochemical cycling) is necessary to understand individual systems and to generate accurate regional carbon budgets. There is an ongoing debate in ecology as to how DOM interacts with the microbial communities that play such an important part in DOM biogeochemistry, and what aspects of DOM help shape the microbial community (e.g. is it species rich, or species poor, mainly active or mainly inactive). Understanding the relationship between species diversity and biogeochemical cycling in different ecosystems is a priority topic for NERC. New experimental approaches and methods mean these questions can now be addressed. This project is investigating these concepts in a system of lakes in West Greenland. These lakes have a range of DOM concentrations, and are being influenced by global change processes such as increased atmospheric nutrient loading and annual warming. Arctic lakes are extremely important in their regional ecology; they occupy significant land area and can act as annual carbon sinks or carbon sources, depending on their characteristics. We will characterise the different DOM components of the water columns of a set of lakes selected to provide a controlled gradient of conditions, and determine the seasonal cycles of accumulation and loss of DOM. In parallel, we will use new molecular biology tools to identify and quantify the diverse microbial communities involved in these processes. We will be able to determine the relationship between microbial community diversity and activity, and how this is influenced by the types of DOM present. We will also conduct experiments to establish which DOM are the most difficult and most easy for particular microbes to breakdown, and whether such processes are influenced by nutrients such as nitrogen. These results will help to assess how the ecology lakes in arctic regions will change over the next few decades, as well as providing important information on the relationships between DOM biogeochemistry and microbial diversity and activity that will be applicable to other aquatic systems. These new data will also contribute to the development of theories of how microbial community are structured, and whether they follow rules determined for larger organisms, or have unique characteristics.

Aerosols and clouds are important components of the Earth's atmosphere, influencing the radiation budget and chemical composition, and affecting human health. The impact of aerosols and clouds on global climate remains one of the largest single uncertainties in understanding previous climate observations and in predicting future climate change. Aerosols and clouds can scatter and absorb sunlight and terrestrial radiation, having a direct effect on climate by altering the balance of incoming solar radiation and outgoing infrared light. Aerosols also have an indirect effect on climate by influencing the albedo and lifetime of clouds, because cloud droplets form from the much smaller aerosol particle seeds on which water can condense. Changes in the number of aerosol particles in the Earth's atmosphere and their size distribution can lead to changes in the number of cloud droplets that form. This indirect effect is poorly constrained and generally counteracts the warming induced by increased levels of greenhouse gases in the atmosphere, exerting a cooling effect on the Earth's climate. The project "Reducing the Uncertainties in Aerosol Hygroscopic Growth", to which this project is linked, seeks to quantify the microphysical properties and processes that control the formation of cloud droplets from aerosol particles in a series of laboratory measurements on single, suspended, aerosol particles using state of the art techniques. These properties can then be used, in a much simplified form, in the computer models used to simulate atmospheric air quality and climate. One of these simplified methods is the "kappa-Köhler theory" created by our international partner (in the USA) on this project. Together, we will do the following: First, we will exchange staff between the Bristol Aerosol Research Centre and the laboratory of our international partner at North Carolina State University for a short period (one focus area will be the viscosity of aerosol components). This will enable an exchange of skills: our work is mostly fundamental, and laboratory-based, whereas our international partner participates extensively in field campaigns of atmospheric measurements. These areas of interest, and associated science, are complementary. Second we will work together to provide a database of values of the aerosol parameter kappa, and web-based tools to carry out calculations that are related to the uptake of water by atmospheric aerosols and their role in the formation of clouds. These tools will be publicly accessible on the Extended Aerosol Inorganics Model website. They should provide a focus for international efforts in this area, and help to spread best practice. Third, will hold a Workshop, hosted with our international partner and with invited experts in the measurement and use of kappa and kappa-Köhler theory, to discuss current problems in the field and to recommend where future effort should be directed. One problem area is the kappa values of the organic components of atmospheric aerosols, whose behaviour and composition are both very complex, making it difficult to relate parameter kappa to composition in a direct or reliable way. The participants will also review the website tools and database, and make recommendations for future development. In addition to the scientific benefits, UK participation and leadership in international atmospheric aerosol research will be advanced by the partnership and links created in this project.

192 inbred lines derived from a single natural population of the fruit fly Drosophila melanogaster (the Drosophila Genetic Reference Panel, DGRP) will have their courtship song recorded and analysed. The design will allow us to measure a range of song parameters, plus collect data on singing rates and mating success. The DGRP lines are part of a coordinated effort by the Drosophila community and are having their genomes sequenced to a high level of coverage. This will allow genome-wide association analyses to be completed for variation in song, and covariation analyses between song and other phenotypes, including mating success. This will provide an unparalleled data set for the analysis of genome-wide associations for variation in important behavioural phenotypes within a single population. Results will be relevant to behaviour genetics, sexual selection and our understanding of the ecological and evolutionary genetics of natural populations.