2TEDA School of Biological Sciences and Biotechnology, Nankai University, TEDA, Tianjin 300457, P. R. China
3Tianjin Key Laboratory for Microbial Functional Genomics, TEDA College, Nankai University, TEDA, Tianjin 300457, P. R. China; E-mail: email@example.com
* This paper is based on a presentation made at the 4th Baltic Conference on Microbial Carbohydrates, Hyytiala Forestry Field Station, Finland, September 19-22, 2010.
# These authors contributed equally to this work.
** To whom correspondence should be addressed.
Received December 24, 2010; Revision received February 3, 2011
The O-polysaccharide (O-antigen) of Salmonella enterica O51 was isolated by mild acid degradation of the lipopolysaccharide and its structure was established using sugar analysis and NMR spectroscopy. The O-antigen of Escherichia coli O23, whose structure was elucidated earlier, possesses a similar structure and differs only in the presence of an additional lateral α-D-Glcp residue at position 6 of the GlcNAc residue in the main chain. Sequencing of the O-antigen gene clusters of S. enterica O51 and E. coli O23 revealed the same genes with a high-level similarity. By comparison with opened gene databases, all genes expected for the synthesis of the common structure of the two O-antigens were assigned functions. It is suggested that the gene clusters of both bacteria originated from a common ancestor, whereas the O-antigen modification in E. coli O23, which, most probably, is induced by prophage genes outside the gene cluster, could be introduced after the species divergence.
KEY WORDS: Salmonella enterica, Escherichia coli, lipopolysaccharide, bacterial polysaccharide, structure, gene cluster, O-antigen