Experiments were performed to study whether the synthesis of the fimbrial colonization factor antigen I (CFA/I) of enterotoxigenic Escherichia coli is affected by glucose. The CFA/I-producing strain H-10407 (O78:H11:CFA/I) was grown in CFA medium containing various concentrations of glucose. Addition of 1% glucose into the medium resulted in a pronounced decrease in CFA/I production by H-10407 as assessed by ELISA, hemagglutination, and electron microscopy. The repressive effect of glucose was reversed by the addition of 10 m M cAMP to the medium. Examination of the promoter sequence of the cfaA gene of the CFA/I operon revealed a consensus binding site for the catabolite activator protein-cAMP complex. With a reporter plasmid containing a fusion of the cfaA promoter, a portion of the cfaA gene, and the lacZ gene, it was shown that the activity of this promoter was influenced by glucose. In a wild-type E. coli strain, addition of 0.5% glucose to the growth medium diminished the promoter activity more than 70%. The cfaA promoter also exhibited a lower level of activity in cya (adenyl cyclase) and crp (cAMP receptor protein) mutants than in the wild-type strain. The addition of 10 m M cAMP resulted in a marked increase in the expression from the cfaA promoter in the cya but not in the crp mutant. These results suggest that the suppressive effect of glucose in the CFA/I system is mediated via the mechanism of catabolite repression through the cfaA promoter of the CFA/I operon.
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology