Atsushi Iguchi

A complete view of the genetic diversity of the E. coli O-antigen biosynthesis gene cluster

The O antigen constitutes the outermost part of the lipopolysaccharide layer in Gram-negative bacteria. The chemical composition and structure of the O antigen show high levels of variation even within a single species revealing itself as serological diversity. The E. coli O serogroups were designated O1 to O187 and included three pairs of subgroups, O18ab/ac, O28ab/ac, and O112ab/ac and six missing numbers, O31, O47, O67, O72, O93, and O122. The genes required for O-antigen biosynthesis are clustered at a chromosomal locus flanked by the colanic acid biosynthesis gene cluster (wca genes) and the histidine biosynthesis (his) operon. In our previous study, we analyzed the O-antigen biosynthesis gene clusters (O-AGCs) from all 184 known E. coli O serogroups. By comparing sequences we revealed that among the 182 O serogroups (excluding O14 and O57, which contained no O-AGCs at the typical locus) 145 had unique O-AGCs and the other 37 shared identical or very similar O-AGCs, which were placed into 16 groups (Gp1-Gp16). Although most O-antigen processing genes such as wzx (encoding the O-antigen flippase), wzy (encoding the O-antigen polymerase), and the wzm and wzt genes (encoding components of the ABC transporter pathway) showed high levels of DNA sequence diversity (less than 70% identity with the most similar other O-AGCs), there was high sequence conservation within the 16 O-AGC groups (most with ≥ 97% identity). We believe that the remarkable sequence diversity and conservation in the wzx/wzy and wzm/wzt genes is sufficient to make possible the identification of each of the known O serogroups using these sequences. These data will be a valuable basis for developing a systematic molecular O-typing scheme. Our recent work in development of a PCR-based O-typing platform will also be presented.

Iguchi A et al. DNA Res. (in press)