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.

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 (MXAN_2922) as the polyisoprenyl-phosphate hexose-1-phosphate transferase responsible for priming O-antigen synthesis. In heterologous expression experiments, WbaP complemented a Salmonella enterica mutant lacking the endogenous WbaP that primes O-antigen synthesis, indicating that WbaP transfers galactose-1-P to undecaprenyl-phosphate. We also identified WaaL (MXAN_2919), as the O-antigen ligase that joins O-antigen to lipid A-core. Our data also support the previous suggestion that Wzm (MXAN_4622) and Wzt (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 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.