Mapping bacterial bile amidation across the bile salt hydrolase family

Evaluating enzyme activity and specificity in complex microbiomes is challenging. The recent discovery that bacterial bile salt hydrolases (BSHs) also function as transaminases in the human gut microbiome highlights what remains to be disentangled, even within one of the most extensively studied microbiomes. BSHs as transaminases can conjugate bile acids with bioavailable amines to produce bacterial bile amidates (BBAs). The implications of BBAs for human health are rapidly evolving, but our understanding of which BSHs produce which specific BBAs remains limited. Here, we connect BSH sequence and function by evaluating the transaminase activities of 115 BSHs and reveal distinct amine specificities using molecular networking. Additionally, we identify enzymatically generated BBAs distributed across life-stage, tissue-, and disease-specific human samples by mining public metabolomics repositories, highlighting the previously unrecognized catalytic diversity of BSHs and their potential relevance to human health.