ColV plasmid-specific aerobactin synthesis by invasive strains of Escherichia coli

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Abstract
Certain strains of E. coli associated with bacteremia of humans and domestic animals harbor plasmids that promote efficient Fe uptake. The mechanism, which is an important component of the virulence of invasive strains, is indepedent of the enterobactin system for Fe uptake. Plasmid-specified siderophore was assayed by its ability to support the growth of a chelator-deficient mutant in conditions of Fe deprivation. The chelator, which was chemically determined to be a hydroxamate compound, was identical on the basis of field desorption mass spectrometry with aerobactin, a siderophore synthesized by Aerobacter aerogenes. In conditions of Fe stress, aerobactin is secreted into the culture medium of plasmid-bearing E. coli strains. Reconstruction experiments involving a chelator-deficient mutant growing with exogenous chelator suggested that association of a small fraction of the total siderophore synthesized with cellular material is due to transient binding of aerobactin to membrane receptors during active bacterial growth.