Protein synthesis is required for in vivo activation of polysialic acid capsule synthesis in Escherichia coli K1

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Abstract
The kinetics of in vivo expression of the polysialosyl (K1) capsular antigen in E. coli was studied. Growth of E. coli K1 strains at 15.degree. C was previously shown to prevent K1 polysaccharide synthesis. Synthesis is reactivated in cells grown at 15.degree. C after upshift to 37.degree. C. The early expression and resultant morphology of K1 capsular antigen was monitored in temperature upshift experiments by using EM. Morphological stimulation of the capsule was achieved by treatment of cells with an antiserum specific for the .alpha.,2-8-linked polysialosyl antigen. The kinetics of K1 capsule expression in growing cells was measured by bacteriophage adsorption with phage K1F, which required the K1 capsule for binding. The results of temperature upshift experiments showed that capsule first appeared on the cell surface after 10 min. Subsequent bacteriophage binding increased linearly with time until a fully encapsulated state was reached 45 min after upshift. The initial of K1 capsule appearance was dependent on protein synthesis and the addition of chloramphenicol before temperature upshift prevented any expression of the K1 antigen. Chloramphenicol reduced the rate of K1 synthesis when added after temperature upshift. Evidently, protein synthesis is a prerequisite for activation of capsule expression in vivo, but not for subsequent elongation of polysialosyl chains.