Identification of the lipopolysaccharide O‐antigen biosynthesis priming enzyme and the O‐antigen ligase in Myxococcus xanthus: critical role of LPS O‐antigen in motility and development

Summary Myxococcus xanthus is a model bacterium to study social behavior. At the cellular level, the different social behaviors of M. xanthus involve extensive cell–cell contacts. Here, we used bioinformatics, genetics, heterologous expression and biochemical experiments to identify and characterize the key enzymes in M. xanthus implicated in O‐antigen and lipopolysaccharide (LPS) biosynthesis and examined the role of LPS O‐antigen in M. xanthus social behaviors. We identified WbaP Mx (MXAN_2922) as the polyisoprenyl ‐ phosphate hexose‐1‐phosphate transferase responsible for priming O‐antigen synthesis. In heterologous expression experiments, WbaP Mx complemented a Salmonella enterica mutant lacking the endogenous WbaP that primes O‐antigen synthesis, indicating that WbaP Mx transfers galactose‐1‐P to undecaprenyl‐phosphate. We also identified WaaL Mx (MXAN_2919), as the O‐antigen ligase that joins O‐antigen to lipid A‐core. Our data also support the previous suggestion that Wzm Mx (MXAN_4622) and Wzt Mx (MXAN_4623) form the Wzm/Wzt ABC transporter. We show that mutations that block different steps in LPS O‐antigen synthesis can cause pleiotropic phenotypes. Also, using a wbaP Mx deletion mutant, we revisited the role of LPS O‐antigen and demonstrate that it is important for gliding motility, conditionally important for type IV pili‐dependent motility and required to complete the developmental program leading to the formation of spore‐filled fruiting bodies.