Genomic and biochemical analysis reveals fermented product of a putative novel Romboutsia species involves the glycometabolism of tilapia

Fish have a restricted capacity to utilize carbohydrates. Gut microbiota contribute to carbohydrate degradation in the host. The connection between the intestinal microbiota and carbohydrate metabolism is not well known in fish. We found that when feed was transformed from zooplankton-based to plant-based diet, the population of genus Romboutsia in tilapia gut increased. We inferred that the abundance of the genus Romboutsia was positively correlated with dietary sugar levels. Then, a strain of genus Romboutsia was obtained and designated MY01. Strain MY01 was a novel species of Romboutsia based on its genomic analysis. Many genes involved in carbohydrate metabolism were found in its genome, including Carbohydrate Active enZymes (CAZymes) genes associated with dietary fiber fermentation. An increased quantity of short-chain fatty acids (SCFAs) and decreased quantity of carbohydrates in feed fermented with MY01 were revealed by GC-MS and HPLC analysis. Fermented feed with MY01 increased the insulin content and decreased the glucose content of tilapia serum. Our in vivo and in vitro results are the first to suggest that fermented feed with Romboutsia regulates the tilapia glycometabolism by producing SCFAs to stimulate insulin secretion, and by reducing carbohydrates content of feed simultaneously to decrease blood glucose eventually. In further, the study provides a potential source of SCFAs production.