Elucidating the lipopolysaccharide biosynthetic pathway in Myxococcus xanthus

Bacteria possess surface polysaccharides that can interact with the environment and fulfill different functions including mediating host/pathogen interactions as well as acting as a first barrier to protect cells from desiccation stress, predation or immunological reaction.
Cells of the rod-shaped, Gram negative deltaproteobacterium Myxococcus xanthus can move by means of two genetically distinct motility systems: T4P-dependent motility and gliding motility. Exopolysaccharides and the O-antigen part of the lipopolysaccharide (LPS) are essential for T4P-dependent motility in M. xanthus, but little is known about the biosynthetic machineries, regulation and composition of these different surface polysaccharides. Three different machineries for biosynthesis of surface polysaccharides have been described in other bacteria. Here, we identified genes for 15 proteins in M. xanthus with homology to proteins of the Wzx-Wzy dependent pathway involved in surface polysaccharide synthesis as well as two genes for proteins of an ABC transporter previously described to be important for O-antigen transport. Genetic analyses of these 17 genes in combination with measurements of EPS and LPS accumulation allowed us to elucidate in details the biosynthetic pathway for LPS. Moreover, the overall layout of the EPS pathway has been identified.