Polymorphism, duplication, and IS1-mediated rearrangement in the chromosomal his-rfb-gnd region of Escherichia coli strains with group IA and capsular K antigens

Abstract

Individual Escherichia coli strains produce several cell surface polysaccharides. In E. coli E69, the his region of the chromosome contains the rfb (serotype O9 lipopolysaccharide O-antigen biosynthesis) and cps (serotype K30 group IA capsular polysaccharide biosynthesis) loci. Polymorphisms in this region of the Escherichia coli chromosome reflect extensive antigenic diversity in the species. Previously, we reported a duplication of the manC-manB genes, encoding enzymes involved in GDP-mannose formation, upstream of rfb in strain E69 (P. Jayaratne et al., J. Bacteriol. 176:3126-3139, 1994). Here we show that one of the manC-manB copies is flanked by IS1 elements, providing a potential mechanism for the gene duplication. Adjacent to manB 1 on the IS1-flanked segment is a further open reading frame (ugd), encoding uridine-5 -diphosphoglucose dehydrogenase. The Ugd enzyme is responsible for the production of UDP-glucuronic acid, a precursor required for K30 antigen synthesis. Construction of a chromosomal ugd::Gm r insertion mutation demonstrated the essential role for Ugd in the biosynthesis of the K30 antigen and confirmed that there is no additional functional ugd copy in strain E69. PCR amplification and Southern hybridization were used to examine the distribution of IS1 elements and ugd genes in the vicinity of rfb in other E. coli strains, producing different group IA K antigens. The relative order of genes and, where present, IS1 elements was established in these strains. The regions adjacent to rfb in these strains are highly variable in both size and gene order, but in all cases where a ugd homolog was present, it was found near rfb. The presence of IS1 elements in the rfb regions of several of these strains provides a potential mechanism for recombination and deletion events which could contribute to the antigenic diversity seen in surface polysaccharides.

Characterization of the Structure and Biological Functions of a Capsular Polysaccharide Produced by Staphylococcus saprophyticus

“…The putative gene products of capD Ssp and capL Ssp show homology to bacterial proteins involved in UDP-D-FucNAc biosynthesis, whereas CapK Ssp is a putative UDP-FucNAc transferase. The gtaB gene upstream of the cap Ssp locus (encoding a putative UTP-glucose-1-phosphate uridyltransferase) and capI Ssp (encoding a putative UDP-glucose-6-dehydrogenase) are homologous to bacterial genes involved in UDP-glucuronic acid synthesis (6,56 (Fig. 1), and the last two ORFs appear to be truncated Table S1 in the supplemental material.…”

Molecular and functional analysis of genes required for expression of group IB K antigens in Escherichia coli : characterization of the his‐region containing gene clusters for multiple cell‐surface polysaccharides

“…upstream of rfb O9 , although there is extensive variation in DNA between these genes in different group IA K serotypes (Jayaratne et al, 1994;Drummelsmith et al, 1997). PCR primers (PAA2 and PAA13; Fig.…”

Transcriptional organization and regulation of the Escherichia coli K30 group 1 capsule biosynthesis (cps) gene cluster

“…The presence of the RcsAB box upstream of galF seems to be a unique feature of the K. pneumoniae and E. coli group 1 capsule producers. Comparison of the gene order in this region of the chromosome in group 1 capsule producers with those of isolates that make colanic acid indicates that a number of chromosomal rearrangements have occurred (Drummelsmith et al ., 1997). Of particular interest is the location of galF .…”