Anaerobic choline metabolism in microcompartments promotes growth and swarming of P roteus mirabilis

Gammaproteobacteria are important gut microbes but only persist at low levels in the healthy gut. The ecology of G ammaproteobacteria in the gut environment is poorly understood. Here, we demonstrate that choline is an important growth substrate for representatives of G ammaproteobacteria. Using P roteus mirabilis as a model, we investigate the role of choline metabolism and demonstrate that the cut C gene, encoding a choline‐trimethylamine lyase, is essential for choline degradation to trimethylamine by targeted mutagenesis of cut C and subsequent complementation experiments. P roteus mirabilis can rapidly utilize choline to enhance growth rate and cell yield in broth culture. Importantly, choline also enhances swarming‐associated colony expansion of P . mirabilis under anaerobic conditions on a solid surface. Comparative transcriptomics demonstrated that choline not only induces choline‐trimethylamine lyase but also genes encoding shell proteins for the formation of bacterial microcompartments. Subsequent analyses by transmission electron microscopy confirmed the presence of such novel microcompartments in cells cultivated in liquid broth and hyper‐flagellated swarmer cells from solid medium. Together, our study reveals choline metabolism as an adaptation strategy for P . mirabilis and contributes to better understand the ecology of this bacterium in health and disease.