2nd Place: Using synthetic diets to examine how the gut microbiome responds to dietary carbohydrate source in the omnivorous cockroach Periplaneta americana

The omnivorous American cockroach, Periplaneta americana, hosts a bustling and diverse microbial community that contributes heavily to its behavioral patterns, immune capability, and nutrient acquisition from indigestible feedstuffs. Unlike mammals, which typically show large changes in gut community after dietary changes, P. americana retains remarkable microbiome stability during drastic whole-food diet shifts. However, we have observed changes in response to altering dietary carbohydrate source in synthetic diets with controlled protein and micronutrient content. In particular, we have identified xylan, a highly abundant hemicellulose, as having a strong impact on the cockroach hindgut microbiome relative to cockroaches fed either whole food diets or synthetic diets dominated by microcrystalline cellulose or starch. Xylan-related changes in microbial community was observed to occur despite different levels of protein and micronutrients. These responses were not replicated in diets containing the primary monomer, xylose, as the sole carbohydrate source. When diets with a range of xylan:microcrystalline cellulose ratios were utilized, we observed a variety of responses among individual xylan-responsive taxa. The functional implications of these responses are being explored further via measurement of volatile fatty acids in hindgut extracts as well as analysis of the hindgut metatranscriptome and host transcriptomes during xylan dietary treatment. This research highlights how the dietary flexibility of cockroaches can be harnessed in combination with synthetic diets to generate new insight into host and microbial interactions underlying changes in gut microbiome structure and function.