Cloning and analysis of gene clusters for production of the Escherichia coli K10 and K54 antigens: identification of a new group of serA-linked capsule gene clusters

Abstract

The polysaccharide capsules of Escherichia coli have been classified into three groups: I, II, and I/II. The third group, I/II, has been poorly studied and possesses characteristics of both group I and group II capsules. In this report, we describe the cloning of the K10 and K54 capsule gene clusters, two representatives of group I/II capsules. Probes taken from DNA flanking regions 1 and 3 of the group II capsule clusters hybridized to these group I/II clones, confirming that the group I/II capsule genes are flanked by the same DNA and are therefore located in the same serA-linked region of the chromosome as group II capsule gene clusters. Southern blotting showed that homologous sequences were present in both the K10 and K54 capsule gene clusters and in other group I/II strains. No homology was detected between these sequences and the chromosomal DNA of either a group I or a group II strain. Likewise, no homology was detected to the chromosomal DNA of either a K11 or K19 strain, both of which had previously been classified as group I/II strains. In the K10 and K54 capsule gene clusters, these conserved sequences flanked a serotype-specific region in a manner analogous to group II capsule gene organization. Complementation of mutations in the kpsE, kpsD, and kpsC genes in region 1 of the K5 capsule gene cluster by subclones of the K10 and K54 capsule gene clusters indicated that certain stages in the export of group II and I/II capsules may be conserved. In the light of the findings presented here, we suggest that the group I/II capsule gene clusters are sufficiently different from group II capsule gene clusters to justify their renaming as group III.

Computer-based analyses of the protein constituents of transport systems catalysing export of complex carbohydrates in bacteria

“…It has been noted previously that Gram-negative bacterial CPS and EPS export systems may require the presence of system-specific auxiliary proteins (Boulnois & Roberts, 1990;Kroll et al, 1990;Frosch et al, 1991;Hashimoto et al, 1993 ;Pearce & Roberts, 1995). These auxiliary proteins are typically encoded within operons or gene clusters concerned with complex carbohydrate biosynthesis and export.…”

“…The various carbohydrate-containing constituents localized to the cell surface are frequently essential virulence factors of pathogenic bacteria as they provide protective functions that allow the organism to combat host defence mechanisms (Hornick et al, 1970;Robbins & Robbins, 1984; Pearce & Roberts, 1995). These macromolecules often exhibit the characteristic of phase variation, allowing the bacteria to successfully evade the immune system of the host (Saier & Jacobson, 1984;Bartlett et al, 1988;Seifert & So, 1988;Dybvig, 1993).…”

“…In addition to recognition functions, carbohydrates provide protective functions to the cell that produces them (Jann & Jann, 1990 1992; Bik et al, 1995;Roberts, 1995). The presence of cytoplasmically synthesized hydrophilic macromolecules within or external to the cell envelope implies the existence of transport mechanisms that allow export of biosynthetic intermediates or the final products of biosynthesis across the cytoplasmic membrane (Kroll et al, 1990;Smith et al, 1990;Manning et al, 1995;Rosenow et al, 1995).…”

The localization of KpsC, S and T, and KfiA, C and D proteins involved in the biosynthesis of the Escherichia coli K5 capsular polysaccharide: evidence for a membrane-bound complex

“…Escherichia coli produces more than 80 chemically and serologically distinct capsules, called K antigens (Jann & Jann, 1990, 1992. These capsules have been separated into three groups, I, I1 and 111, on the basis of chemical composition, molecular mass, intergenic relationships and regulation of expression (Jann & Jann, 1990;Pearce & Roberts, 1995). The majority of extra-intestinal isolates of E. coli associated with invasive disease express group I1 capsules, with particular capsules being associated with certain diseases (Gransden et al, 1990).…”

Bacterial polysaccharides in sickness and in health

“…On the basis of a number of biochemical and genetic criteria, E. coli capsules were originally divided into two groups, I and I1 (Jann & J a m , 1987). Recently, this classification has been re-defined such that there are now at least three groups of capsule gene clusters (Pearce & Roberts, 1995). By far the best studied are the group I1 capsules.…”