Nitrogen fixation in the human gut by sulphate-reducing bacteria

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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 contentDetermine the influence of vegan diets on nitrogen fixation by D. diazotrophicus and identify key interactions within a complex microbiotaEvaluate the impact of D. diazotrophicus on the host's nitrogen pool and gut permeabilityImplicationsMy 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.