Bile salt hydrolase catalyses formation of amine-conjugated bile acids

Bacteria in the gastrointestinal tract produce amino acid bile acid amidates that can affect host-mediated metabolic processes1-6; however, the bacterial gene(s) responsible for their production remain unknown. Herein, we report that bile salt hydrolase (BSH) possesses dual functions in bile acid metabolism. Specifically, we identified a previously unknown role for BSH as an amine N-acyltransferase that conjugates amines to bile acids, thus forming bacterial bile acid amidates (BBAAs). To characterize this amine N-acyltransferase BSH activity, we used pharmacological inhibition of BSH, heterologous expression of bsh and mutants in Escherichia coli and bsh knockout and complementation in Bacteroides fragilis to demonstrate that BSH generates BBAAs. We further show in a human infant cohort that BBAA production is positively correlated with the colonization of bsh-expressing bacteria. Lastly, we report that in cell culture models, BBAAs activate host ligand-activated transcription factors including the pregnane X receptor and the aryl hydrocarbon receptor. These findings enhance our understanding of how gut bacteria, through the promiscuous actions of BSH, have a significant role in regulating the bile acid metabolic network.

Control of bacterial second messenger signaling and motility by heme-based direct oxygen-sensing proteins

Bacteria sense and respond to their environment, allowing them to maximize their survival and growth under changing conditions, such as oxygen levels. Direct oxygen-sensing proteins allow bacteria to rapidly sense concentration changes and adapt by regulating signaling pathways and/or cellular machinery. Recent work has identified roles for direct oxygen-sensing proteins in controlling second messenger levels and motility machinery, as well as effects on biofilm formation, virulence, and motility. In this review, we discuss recent progress in understanding O2-dependent regulation of cyclic di-GMP signaling and motility and highlight the emerging importance in controlling bacterial physiology and behavior.

In Vitro Measurement of Gas-Dependent and Redox-Sensitive Diguanylate Cyclase Activity

Bacteria sense and respond to gaseous ligand changes in the environment to regulate a multitude of behaviors, including the production of the secondary messengers cyclic di-GMP. Gas sensing can be difficult to measure due to the high concentration of the oxygen in the atmosphere, particularly in redox-sensitive systems. Here, we describe a method for anaerobic quantification of cyclic di-GMP production which can be used to measure the impact of molecular oxygen, nitric oxide, and carbon monoxide on the catalysis of a diguanylate cyclase-containing protein and the possible pitfalls in the experimental procedure.