Abstract
Recent work on bile salt hydrolases (BSHs) in Gram-negative bacteria, such as Bacteroides, has primarily focused on how they can impact host physiology. However, the benefits bile acid metabolism confers to the bacterium that performs it are not well understood. In this study, we set out to define if and how Bacteroides thetaiotaomicron (B. theta) uses its BSHs and hydroxysteroid dehydrogenase to modify bile acids to provide a fitness advantage for itself in vitro and in vivo. Genes encoding bile acid-altering enzymes were able to impact how B. theta responds to nutrient limitation in the presence of bile acids, specifically carbohydrate metabolism, affecting many polysaccharide utilization loci. This suggests that B. theta may be able to shift its metabolism, specifically its ability to target different complex glycans including host mucin, when it comes into contact with specific bile acids in the gut.