Molecular studies of Escherichia coli capsule gene clusters
Molecular studies of Escherichia coli capsule gene clusters C. Rachel Drake Escherichia coli can produce a large number (over 70) of structurally distinct capsular polysaccharide (K antigens) which have previously been divided into two groups. Group II K antigens are encoded by kps near serA. The kps genes are homologous between group II capsule gene clusters which encode chemically distinct K antigens. Genes encoding the K4 antigen (group II), an unusual substituted polymer (a fructo-sylated chondroitin), were cloned and expressed in E. coli K-12 and shown to contain the group II kps determinants. By nucleotide sequence analysis it was shown that the 3' end of one group II capsule gene, kpsS, is different in the K1, K4 and K5 capsule gene clusters. It was demonstrated that strains expressing a group I capsule do not carry the group II kps determinants on the chromosome. The K3, K10, K11 and K54 capsules have characteristics of both groups I and II and were also shown to lack the group II capsule genes despite the K10 and K54 capsule genes having previously been mapped near serA. The existence of a third capsule group, group I/II, encoded by genes distinct from the group II capsule genes yet located in the same region of the chromosome is formally proposed. An unsuccessful attempt was made to clone the K9 antigen (group I) biosynthesis genes. DNA flanking the K1 and K4 antigen gene clusters was used as probes in Southern blot analysis of different E. coli isolates and was shown to be a common component of the E. coli chromosome. The K1, K4 and K5 capsule gene clusters appear to be located at the same chromosomal location. DNA adjacent to one end of the K4 capsule gene cluster was highly polymorphic and present in more than one copy in some strains. The organisation and variability of the serA region of the E. coli chromosome is discussed.