Structure and gene cluster of the O antigen of Escherichia coli F17, a candidate for a new O-serogroup

摘要

Escherichia coli F17 isolated from horse feces was studied in respect to the O antigen (O-polysaccharide) structure and genetics. The lipopolysaccharide was isolated by phenol-water extraction of bacterial cells and cleaved by mild acid hydrolysis to yield the O polysaccharide, which was studied by sugar analysis and selective solvolysis with CF3CO2H along with one- and two-dimensional H-1 and C-13 NMR spectroscopy. The O polysaccharide was found to have a branched pentasaccharide repeat (O-unit) containing one residue each of D-galactose, D-man-nose, L-rhamnose, D-glucuronic acid, and N-acetyl-D-glucosamine; about 2/3 units bear a side-chain glucose residue. To our knowledge, the F17 O-polysaccharide structure established is unique among known bacterial polysaccharide structures. The O-antigen gene cluster of E. coli F17 between the conserved genes galF and gnd was sequenced and found to be 99% identical to that of E. coli 102,755 assigned to a novel OgN8 genotype (A. Iguchi, S. lyoda, K. Seto, H. Nishii, M. Ohnishi, H. Mekata, Y. Ogura, T. Hayashi, Front. MicrobioL 7 (2016) 765). Genes in the cluster were annotated taking into account the F17 O-polysaccharide structure. The data obtained confirm that E. coil F17 and E. coli strains belonging to the OgN8 genotype can be considered as a candidate to a new E. coli O-serogroup. The O antigen of this novel type was demonstrated to make for an effective shield protecting the intimate outer membrane surface of bacteria from direct interaction with bacteriophages. (C) 2018 Elsevier B.V. All rights reserved.