bioRxiv2020
Prebiotics confer benefits to human health often by promoting the growth of gut bacteria that produce metabolites valuable to the human body, such as short chain fatty acids (SCFAs). While prebiotic selection has strongly focused on maximizing the production of SCFAs, less attention has been paid to gases, a byproduct of SCFA production that also has physiological effects on the human body. Here, we investigate how the content and volume of gas production by human gut microbiota is affected by the chemical composition of the prebiotic and by the composition of the microbiota. We first constructed a linear systems model based on mass and electron balance and compared the theoretical product range of two prebiotics, inulin and pectin. Modeling shows that pectin is more restricted in product space, with less potential for H2 but more potential for CO2 production. An ex vivo experimental system showed pectin degradation produced significantly less H2 than inulin, but CO2 production fell outside the theoretical product range, suggesting fermentation of fecal debris. Microbial community composition also impacted results: methane production was dependent on the presence of Methanobacteria, while inter-individual differences in H2 production during inulin degradation was driven by a Lachnospiraceae taxon. Overall, these results suggest that both the chemistry of the prebiotic and the composition of the microbiota are relevant to gas production. Metabolic processes that are relatively prevalent in the microbiome, such as H2 production will depend more on substrate, while rare metabolisms like methanogenesis depend more strongly on microbiome composition. ImportancePrebiotic fermentation in the gut often leads to the co-production of short chain fatty acids (SCFAs) and gases. While excess gas production can be a potential problem for those with functional gut disorders, gas production is rarely taken into account during prebiotic design. In this study, we combined the use of theoretical models and an ex vivo experimental platform to illustrate that both the chemical composition of the prebiotic and the community composition of the human gut microbiota can affect the volume and content of gas production during prebiotic fermentation. Specifically, more prevalent metabolic processes such as hydrogen production was strongly affected by the oxidation state of the probiotic, while rare metabolisms such as methane production was less affected by the chemical nature of the substrate and entirely dependent on the presence of Methanobacteria in the microbiota.