CHARACTERIZATION OF RCSB AND RCSC FROM ESCHERICHIA-COLI 09 - K30 H12 AND EXAMINATION OF THE ROLE OF THE RCS REGULATORY SYSTEM IN EXPRESSIONOF GROUP-I CAPSULAR POLYSACCHARIDES

In Escherichia coli K-12, RcsC and RcsB are thought to act as the sens or and effector components, respectively, of a two-component regulator y system which regulates expression of the slime polysaccharide colani c acid (V. Stout and S. Gottesman, J. Bacteriol. 172:659-669, 1990). H ere, we report the cloning and DNA sequence of a 4.3-kb region contain ing rcsC and rcsB from E. coli O9:K30:H12. This strain does not produc e colanic acid but does synthesize a K30 (group 1) capsular polysaccha ride. The rcsB gene from E. coli K30 (rcsB(K30)) is identical to the r csB gene from E. coli K-12 (rcsB(K-12)). rcsC(K30) has 16 nucleotide c hanges, resulting in six amino acid changes in the predicted protein. To examine the function of the rcs regulatory system in expression of the K30 capsular polysaccharide, chromosomal insertion mutations were constructed in E. coli 09:K30:H12 to independently inactivate rcsB,30 and the auxiliary positive regulator rcsA(K30). Strains with these mut ations maintained wild-type levels of K30 capsular polysaccharide expr ession and still produced a K30 capsule, indicating that the rcs syste m is not essential for expression of low levels of the group I capsula r polysaccharide in lon+ E. coli K30. However, K30 synthesis is increa sed by introduction of a multicopy plasmid carrying rcsB(K30). K30 pol ysaccharide expression is also markedly elevated in an rcsB(K30)-depen dent fashion by a mutation in rcsC(K30), suggesting that the rcs syste m is involved in high levels of synthesis. To determine whether the in volvement of the rcs system in E. coli K30 expression is typical of gr oup I (K antigen) capsules, multicopy rcsB(K30) was introduced into 22 additional strains with structurally different group I capsules. All showed an increase in mucoid phenotype, and the polysaccharides produc ed in the presence and absence of multicopy rcsB(K30) were examined. I t is has been suggested that E. coli strains with group I capsules can be subdivided based on K antigen structure. For the first time, we sh ow that strains with group I capsules can also be subdivided by the ab ility to produce colanic acid. Group IA contains capsular polysacchari des (including K30) with repeating-unit structures lacking amino sugar s, and expression of group IA capsular polysaccharides is increased by multicopy rcsB(K30). Group IB capsular polysaccharides all contain am ino sugars. In group IB strains, multicopy rcsB(K30) activates synthes is of colanic acid.