Abstract
The coordinate control of virulence determinants in pathogenic microorganisms is largely based upon the ability of these microbes to rapidly adapt to the environment presented by their host. Essentially all microbial pathogens have evolved specific mechanisms for the assimilation of sufficient concentrations of iron from their environment to support growth. It is remarkable that sensing the available concentration of iron provides not only a signal for siderophore expression, but also a regulatory signal for the expression of a wide variety of bacterial toxins and other virulence factors (reviewed in ref. 1). In Escherichia coli it is widely known that the coordinate regulation of iron-sensitive genes is mediated by Fur (ferric uptake regulator). Once it is activated by iron, Fur has been shown to function as a global regulatory element controlling the expression of regulons that are distributed throughout the E. coli chromosome. Moreover, it is now clear that the iron-mediated regulation of virulence genes in a number of Gram-negative pathogens is also coordinated by a family of closely related proteins that are homologous to Fur.