COEXPRESSION OF COLANIC ACID AND SEROTYPE-SPECIFIC CAPSULAR POLYSACCHARIDES IN ESCHERICHIA-COLI STRAINS WITH GROUP-II K-ANTIGENS

In Escherichia coli K-12, the rcsA and rcsB gene products are positive regulators in expression of the slime polysaccharide colanic acid. We have previously demonstrated the presence of rcsA sequences in E. col i K1 and K5, strains with group 11 capsular K antigens, and shown that introduction of multicopy rcsA into these strains results in the expr ession of colanic acid. We report here the presence of rcsB sequences in E. coli K1 and K5 and demonstrate that RcsB also plays a role in th e biosynthesis of colanic acid in strains with group II K antigens. In E. coli K1 and K5 grown at 37-degrees-C, multicopy rcsB and the resul ting induction of colanic acid synthesis had no significant effect on synthesis of the group II K antigens. K-antigen-specific sugar transfe rase activities were not significantly different in the presence or ab sence of multicopy rcsB, and introduction of a cps mutation to elimina te colanic acid biosynthesis in a K1-derivative strain did not influen ce the activity of the polysialyltransferase enzyme responsible for sy nthesis of the K1 polymer. Furthermore, immunoelectron microscopy show ed no detectable difference in the size or distribution of the group I I K-antigen capsular layer in cells which produced colanic acid. Colan ic acid expression therefore does not appear to significantly affect s ynthesis of the group II K-antigen capsule and, unlike for group I K a ntigens, expression of group II K antigens is not positively regulated by the rcs system.