Cloning and analysis of the Escherichia coli K10 and K54 capsule gene clusters
thesisposted on 15.12.2014, 10:33 by Rowan. Pearce
Escherichia coli can produce a large number of structurally distinct capsular polysaccharides (K antigens). These polysaccharide capsules 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. These studies 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 hybridised 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. At high stringency, no homology was detected between these sequences and the chromosomal DNA of either a group I or 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. An attempt was made to map the position of these two capsule gene clusters on the E. coli chromosome.;In the K10 and K54 capsule gene clusters, the conserved sequences flanked a sereotype-specific region in a manner analogous to group II capsule gene organisation. 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 group I/II capsules may be conserved. Sequencing analyses were performed to determine the extent of DNA homology between certain of the K10 and K5 capsule genes. In the light of these findings it is suggested that group I/II capsule gene clusters are sufficiently different from group II capsule gene clusters to justify their renaming as group III. The organisation and variability of the serA region of the E. coli chromosome is discussed.