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

Abstract

Group 1 capsules of Escherichia coli are similar to the capsules produced by strains of Klebsiella spp. in terms of structure, genetics, and patterns of expression. The striking similarities between the capsules of these organisms prompted a more detailed investigation of the cps loci encoding group 1 capsule synthesis. Six strains of K. pneumoniae and 12 strains of E. coli 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. Thewza and wzc genes are required for translocation and surface assembly of E. coli K30 antigen. The conservation of these genes points to a common pathway for capsule translocation. A characteristic JUMPstart sequence was identified upstream of each cluster which may function in conjunction with RfaH to inhibit transcriptional termination at a stem-loop structure found immediately downstream of the “translocation-surface assembly” region of the cluster. Interestingly, the sequence upstream of thecps clusters in five E. coli strains and oneKlebsiella strain indicated the presence of IS elements. We propose that the IS elements were responsible for the transfer of thecps locus between organisms and that they may continue to mediate recombination between strains.

Complexity of cyanobacterial exopolysaccharides: composition, structures, inducing factors and putative genes involved in their biosynthesis and assembly

“…Despite the variety of bacterial exopolysaccharides, bacteria use a limited repertoire of assembly and secretion strategies, which are represented in E. coli (Whitfield & Roberts, 1999;Whitfield & Paiment, 2003;Whitfield, 2006). For this organism, two models have been proposed for the biosynthesis and assembly of the different types of capsules based on genetic and biochemical criteria, with the one proposed for the capsules of groups 1 and 4 being the most common among Gram-negative bacteria (Rahn et al, 1999;Whitfield, 2006;Whitfield & Larue, 2008). This mechanism is Wzy-dependent, in contrast to the mechanism for groups 2 and 3 capsules, which are assembled via ABC-transporterdependent pathways (Whitfield, 2006).…”

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

“…Previous studies in our laboratory identified a potential stem-loop structure in the intergenic region between wzc and wbaP (Rahn et al, 1999). To assess the ability of the relevant DNA fragments from E. coli B44 to terminate transcription, a number of constructs were made using a termination-probe vector, pHV100 (Peabody et al, 1989).…”

“…Genes early in the cluster are necessary for high-level polymerization and surface assembly of the CPS and include wza (an outer membrane lipoprotein), wzb (an acid phosphatase) and wzc (an inner membrane tyrosine autokinase) (Drummelsmith and Whitfield, 2000;Wugeditsch et al ., 2001). The wza , wzb and wzc genes are conserved in many other organisms that produce group 1-like polymers, including colanic acid in E. coli K-12 (Stevenson et al ., 1996), exopolysaccharide in Erwinia amylovora (Bugert and Geider, 1995) and capsule in Klebsiella pneumoniae (Arakawa et al ., 1995;Rahn et al ., 1999), indicating a conserved pathway for the surface expression of these polysaccharides. An examination of a number of capsule clusters from K. pneumoniae and E. coli has shown that the operons are highly conserved not only in organization, but also in nucleotide sequence between homologous genes, particularly wza , wzb and wzc .…”

“…components of a Wzy-dependent polymerization system are found later in the operon. The genetic organization and gene contents of the group 1 capsule biosynthesis loci are similar to the colanic acid cluster ( cps ) of E. coli K-12 (Stevenson et al ., 1996;Rahn et al ., 1999) (Fig. 1).…”

“…Interestingly, E. coli strains that make group 1 capsules do not have the ability to produce colanic acid (Keenleyside et al ., 1992). A number of gene insertions and rearrangements appear to have accompanied the loss of the colanic acid locus and acquisition of the group 1 capsule cluster (Rahn et al ., 1999). Unlike colanic acid, group 1 capsules are essential for virulence in the strains that produce them (Smith and Huggins, 1978;Hadad and Gyles, 1982).…”