O-Antigen repeat unit biosynthesis - Halothermothrix orenii

O-antigen is a repetitive glycan polymer synthesized as the most variable part in the lipopolysaccharide (LPS) biosynthesis (map00541). Structural diversity of O-antigen repeat units results from genetic diversity as summarized here for completely sequenced Escherichia coli genomes, many of which are for pathogenic strains.