Serine hydrolases play important roles in signaling and human metabolism, yet little is known about the functions of these enzymes in gut commensal bacteria. Using bioinformatics and chemoproteomics, we identify serine hydrolases in the gut commensal Bacteroides thetaiotaomicron that are specific to the Bacteroidetes phylum. Two are predicted homologs of the human protease dipeptidyl peptidase 4 (hDPP4), a key enzyme that regulates insulin signaling. Functional studies reveal that BT4193 is a true homolog of hDPP4 while the other is misannotated and is a proline-specific triaminopeptidase. We demonstrate that BT4193 is important for envelope integrity and is inhibited by FDA-approved type 2 diabetes drugs that target hDPP4. Loss of BT4193 reduces B. thetaiotaomicron fitness during in vitro growth within a diverse community. Taken together, our findings suggest that serine hydrolases contribute to gut microbiota dynamics and may be off-targets for existing drugs that could cause unintended impact on the microbiota.
