The species Escherichia coli consists of both commensal and pathogenic clones. The current O‑antigen-based typing scheme of E. coli comprises 174 O-serogroups. The O-antigen is the O‑polysaccharide chain of the lipopolysaccharide on the bacterial cell surface. It consists of many repeats of an oligosaccharide (O-units) and is one of the most variable cell constituents. The diversity of the O-antigen forms is mainly due to variations in the O‑antigen gene cluster, which contains genes for i) synthesis of specific components of the O‑antigens, ii) sugar transfer, and iii) O-antigen processing. Expression of only one O-antigen form and the variations may offer to the bacteria a selective advantage in the niche occupied. Studies of structure and genetics of E. coli O-antigens are helpful for development of diagnostic tools for disease control and prevention.
To date, O-polysaccharide structures have been established in more than 120 E. coli O-serogroups. In this work, we established the structures and characterized the gene clusters of the O-antigens of E. coli O30, O76, O154, and O163, which had not been studied earlier. The O-polysaccharides are composed of linear or branched tetrasaccharide or pentasaccharide O-units and, except for O154 antigen, are acidic due to the presence of d-glucuronic acid. Gene clusters responsible for biosynthesis of these O-antigens were sequenced. Gene functions were tentatively assigned by comparison with sequences in the available databases and found to be in agreement with the corresponding O-antigen structures. The O-antigen structure and the gene cluster organization of E. coli O163 are closely related to those of Salmonella enterica O41, thus indicating the origin of both O‑antigens from a common ancestor.
This work was supported by the Russian Foundation for Basic Research (11-04-01020), the National Natural Science Foundation of China (30900255 and 31111120026), and Tianjin Research Program of Application Foundation and Advanced Technology (10JCYBJC10100).
