Abstract
The O-antigen is the outermost component of the lipopolysaccharide layer in Gram-negative bacteria, and the variation of O-antigen structure provides the basis for bacterial serological diversity. Here, we determined the O-antigen structure of an Escherichia coli strain, LL004, which is totally different from all of the E. coli serogroups. The tetrasaccharide repeating unit was determined as →4)-β-d-Galp-(1→3)-β-d-GlcpNAc6OAc(~70%)-(1→3)-β-d-GalpA-(1→3)-β-d-GalpNAc-(1→ with monosaccharide analysis and NMR spectra. We also characterized the O-antigen gene cluster of LL004, and sequence analysis showed that it correlated well with the O-antigen structure. Deletion and complementation testing further confirmed its role in O-antigen biosynthesis, and indicated that the O-antigen of LL004 is assembled via the Wzx/Wzy dependent pathway. Our findings, in combination, suggest that LL004 should represent a novel serogroup of E. coli.
Highlights
Lipopolysaccharide (LPS), which is located exclusively in the outermost layer of Gramnegative bacteria, is essential for cell stability and virulence [1]
In E. coli, the genes involved in OAg biosynthesis are clustered, namely the O-antigen biosynthesis gene cluster (O-AGC), and, in most cases, maps at a chromosomal locus flanked by two housekeeping genes, wcaM encoding colanic acid biosynthesis enzyme and hisI encoding phosphoribosyl-AMP cyclohydrolase, respectively [4]
Our results indicate that LL004 may be a novel serogroup a novel serogroup of E. coli
Summary
Lipopolysaccharide (LPS), which is located exclusively in the outermost layer of Gramnegative bacteria, is essential for cell stability and virulence [1]. The LPS molecule typically consists of three components: the lipid A that anchors LPS to the outer membrane, the core oligosaccharide that is a non-repeating oligosaccharide, and the O-antigen (OAg), which is a polymer of repeating oligosaccharide (O-units), each normally being composed of two to seven residues from a broad range of sugars and their derivatives [2]. E. coli have been internationally recognized based on the huge variation of its OAg chemical structures [4]. In E. coli, the genes involved in OAg biosynthesis are clustered, namely the O-antigen biosynthesis gene cluster (O-AGC), and, in most cases, maps at a chromosomal locus flanked by two housekeeping genes, wcaM encoding colanic acid biosynthesis enzyme and hisI encoding phosphoribosyl-AMP cyclohydrolase, respectively [4].
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