Conserved organization in the cps gene clusters for expression of Escherichia coli group 1 K antigens: Relationship to the colanic acid biosynthesis locus and the cps genes from Klebsiella pneumoniae

Group 1 capsules of Escherichia coli are similar to the capsules produced b y strains of Klebsiella spp, in terms of structure, genetics, and patterns of expression. The striking similarities between the capsules of these orga nisms prompted a more detailed investigation of the cps loci encoding group 1 capsule synthesis. Six strains of K, pneumoniae and 12 strains of E. col i were examined. PCR analysis showed that the clusters in these strains are conserved in their chromosomal locations. A highly conserved block of four genes, orfX-wza-wzb-wzc, was identified in all of the strains. The wza and wzc genes are required for translocation and surface assembly of E. coli K 30 antigen. The conservation of these genes points to a common pathway for capsule translocation. A characteristic JUMPstart sequence was identified u pstream of each cluster which may function in conjunction with RfaH to inhi bit transcriptional termination at a stem-loop structure found immediately downstream of the "translocation-surface assembly" region of the cluster. I nterestingly, the sequence upstream of the cps clusters in five E. coli str ains and one Klebsiella strain indicated the presence of IS elements. We pr opose that the IS elements were responsible for the transfer of the cps loc us between organisms and that they may continue to mediate recombination be tween strains.