Bile acids (BAs) comprise heterogenous amphipathic cholesterol-derived molecules that carry out physicochemical and signaling functions. A major site of BA action is the terminal ileum, where enterocytes actively reuptake BAs and express high levels of BA-sensitive nuclear receptors. BA pool size and composition are affected by changes in metabolic health, and vice versa. One of several factors that differentiate BAs is the presence of a hydroxyl group on C12 of the steroid ring. 12α-hydroxylated BAs (12HBAs) are altered in multiple disease settings, but the consequences of 12HBA abundance are incompletely understood. We employed mouse primary ileum organoids to investigate the transcriptional effects of varying 12HBA abundance in BA pools. We identified Slc30a10 as one of the top genes differentially induced by BA pools with varying 12HBA abundance. SLC30A10 is a manganese (Mn) efflux transporter critical for whole-body manganese excretion. We found that BA pools, especially those low in 12HBAs, induce cellular manganese efflux, and that Slc30a10 induction by BA pools is driven primarily by lithocholic acid signaling via the vitamin D receptor. Administration of lithocholic acid or a vitamin D receptor agonist resulted in increased Slc30a10 expression in mouse ileum epithelia. These data demonstrate a previously unknown role for BAs in intestinal control of Mn homeostasis.

A mechanistic understanding of host-microbe interactions in the gut microbiome is hindered by poorly annotated bacterial genomes. While functional genomics can generate large gene-to-phenotype datasets to accelerate gene discovery, their applications to study gut anaerobes have been limited. For instance, most gain-of-function screens of gut bacterial genes have been performed in an aerobic host and included a small number of conditions. To address these challenges, we developed a strategy to barcode expression libraries for high-throughput interrogation of gene functions in competitive fitness assays. We demonstrate the power of this approach to uncover novel phenotypes for uncharacterized genes using pooled libraries constructed from a diverse set of gut Bacteroidales expressed in Bacteroides thetaiotaomicron. We identified new roles in carbohydrate metabolism for nine proteins, including enzymes, transporters, a regulator, and hypothetical proteins from mobile genetic elements. This approach can be readily applied to other organisms and additional phenotypic assays.

Bile acids (BAs) comprise heterogenous amphipathic cholesterol-derived molecules that carry out physicochemical and signaling functions. A major site of BA action is the terminal ileum,