CMP-KDO-synthetase activity in Escherichia coli expressing capsular polysaccharides

The temperature-regulated expression of capsular group II polysaccharides of Escherichia coli (B. Jann and K. Jann, (1990) Curr. Top. Microbiol. Immunol. 150: 19-42) depends on an elevated concentration of CMP-KDO, as evidenced by an increased activity of CMP-KDO synthetase. The increase in activity of CMP-KDO synthetase is observed only in cytoplasmic fractions of bacteria which had been grown at 37 degrees C but not after growth at 18 degrees C. The activity of CMP-KDO synthetase thus parallels the activity of the (membrane-associated) system synthesizing capsules of group II in E. coli. No such dependence of capsule expression on CMP-KDO was observed with E. coli with capsules of group I. A number of E. coli strains with capsular polysaccharides, which on the basis of genetic determination and chemical characteristics are considered as group II capsules, show no temperature regulation of their capsules and do not depend on an elevated CMP-KDO concentration for capsule expression. The capsular polysaccharides of these E. coli strains, which possibly represent a new group of E. coli capsules are tentatively classified as group I/II.