The virulence-associated chrysobactin iron uptake system of Erwinia chrysanthemi 3937 involves an operon encoding transport and biosynthetic functions

The iron assimilation system of Erwinia chrysanthemi 3937 is mediated by the catechol-type siderophore chrysobactin and the outer membrane transport protein Fct. We generated a variety of subclones in high- and low-copy-number vectors from a wild-type recombinant cosmid shown previously to carry the gene cluster fct-cbsA, cbsB, cbsC, cbsE encoding chrysobactin transport and biosynthetic functions, respectively. We studied their expression in Escherichia coli enterobactin-deficient entA, entB, entC, and entE mutants. This provided evidence that the fct and cbs genes are regrouped within a single genetic unit of ca. 8 kb in the following order: fct, cbsC, cbsE, cbsB, and cbsA. The gene boundaries were determined, and the various recombinant plasmids were expressed in Escherichia coli minicells: CbsA and CbsC enzymatic activities were clearly identified as polypeptides with apparent molecular masses of 32,000 and 38,000, respectively.