POLYMORPHISM, DUPLICATION, AND IS1-MEDIATED REARRANGEMENT IN THE CHROMOSOMAL HIS-RFB-GND REGION OF ESCHERICHIA-COLI STRAINS WITH GROUP IA CAPSULAR-K ANTIGENS

Individual Escherichia coli strains produce several cell surface polys accharides. In E. coli E69, tile his region of the chromosome contains the rfb (serotype O9 lipopolysaccharide O-antigen biosynthesis) and c ps (serotype K30 group IA capsular polysaccharide biosynthesis) loci. Polymorphisms in this region of the Escherichia coli chromosome reflec t extensive antigenic diversity in the species, Previously, we reporte d a duplication of the manC-manB genes, encoding enzymes involved in G DP-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 m anC-manB copies is flanked by IS1 elements, providing a potential mech anism for the gene duplication, Adjacent to manB(1) on the IS1-flanked segment is a further open reading frame (ugd), encoding uridine-5'-di phosphoglucose dehydrogenase. The Ugd enzyme is responsible for the pr oduction 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 K3 0 antigen and confirmed that there is no additional functional ugd cop y in strain E69, PCR amplification and Southern hybridization were use d to examine the distribution of IS1 elements and ugd genes in the vic inity of rfb in other E. coli strains, producing different group IA K antigens, The relative order of genes and, where present, ISI elements was established in these strains, The regions adjacent to rfb in thes e strains are highly variable in both size and gene order, hut in all cases where a ugd homolog was present, it was found near rfb. The pres ence of IS1 elements in the rfb regions of several of these strains pr ovides a potential mechanism for recombination and deletion events whi ch could contribute to the antigenic diversity seen in surface polysac charides.