Sequence of Escherichia coli O141 O-antigen gene cluster and analyses of its evolutionary history

Lipopolysaccharide(LPS) is one of the major components of the outer membrane of gram-negative bacteria. It is an amphipathic molecule compose of lipid A, a core oligosaccharide and an O-specific antigen. O-antigen, which is a repeat-unit polysaccharide, is a major contribution to the antigenic variability of the bacterial cell surface. The genes of O-antigen gene cluster are responsible for the synthesis of the O-antigen. The O-antigen gene cluster of E. coli O141 was sequenced and found to contain the genes rmlBDAC and manBC for the biosynthesis of nucleotide sugars dTDP-rhamnose and GDP-mannose, respectively, encoding genes for Ounit flippase(wzx), O-antigen polymerase(wzy) and potential transferase genes. The possible biosynthesis pathway for O-antigen of E. coli O141 was proposed. Two genes specific to E. coli O141 were identified. This work provides the basis for a sensitive test by PCR for the rapid detection of E. coli O141. Phylogenetic trees for the rmlB, rmlD, rmlA, and rmlC genes and manB, manC genes were generated and the comparisons were made among different strains. We find that these genes are typical E. coli genes and might have been involved in recombination events between O-antigen gene clusters.