A new high-affinity system for iron transport, associated with the presence of ColV plasmids, has been detected in Escherichia coli and partially characterized. The presence of such "iron-transport plasmids" in E. coli cells that are defective in enterochelin-mediated transport of iron enabled them to grow in media to which 2,2'-dipyridyl had been added to reduce availability of iron. In addition, the presence of plasmid deoxyribonucleic acid in a mutant defective in enterochelin biosynthesis was associated with a marked increase in the rate of radioactive-iron uptake. Plasmid-determined uptake of iron was distinct from previously recognized systems for iron transport in E. coli K-12, and the colicin V molecule appeared not to be directly involved. Hydroxylamine-nitrogen could be detected in cell pellets of ColV+ cultures, and similar material was detected in supernatant fluids of late log- or stationary-phase cultures. The hydroxamate material was not detected in cell pellets or culture supernatants of strains from which plasmids had been eliminated, and a 95% decrease in hydroxamate synthesis was observed when cells were grown in minimal medium containing 2 microM iron.

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A total of 476 strains of Escherichia coli isolated from humans, pigs, cattle, poultry, potable water, or effluent were examined for iron-suppressible ability to produce hydroxamate. Isolates able to produce such material (Hyd' isolates) are presumed to be able to carry out hydroxamate-dependent transport of iron. The percentages of Hyd' isolates found among E. coli isolated from the feces of breast-fed babies (71%), adults (46%), milk-fed calves (32%), or poultry (28%) were significantly greater (P < 0.01) than the percentages isolated from potable water and effluent (6%) or from the feces of suckling piglets (6%), weaned pigs (6%), or weaned cattle (4%). The percentages of Hyd' isolates found among E. coli associated with diarrhea in humans (51%), weaned pigs (7%) or calves (25%) were not significantly different (P > 0.1) from those found among strains isolated from corresponding nondiarrheic hosts. Many of the E. coli isolated from cases of E. coli bacteremia in humans and poultry were Hyd' (64% and 83%, respectively). We conclude that ability to carry out hydroxamate-mediated transport of iron is widely distributed among natural isolates of E. coli but that the distribution of Abstr. Annu. Meet. Aust. Soc. Microbiol. 1981, C6, p54).