Vibrio cholerae iron transport systems: Roles of heme and siderophore iron transport in virulence and identification of a gene associated with multiple iron transport systems

Abstract

Vibrio cholerae iron transport mutants were tested for their ability to cause disease in an infant mouse model. The mice were challenged with either the wild-type strain, a vibriobactin synthesis mutant, a heme utilization mutant, or double mutants containing both the vibriobactin synthesis defect and the heme utilization defect. When mice were challenged with 107 bacteria, the ability of the double mutant to survive in the intestines was greatly reduced and that of the heme utilization mutant was slightly reduced compared with that of the wild type or the vibriobactin synthesis mutant. When the inoculum size was reduced 10-fold, all of the iron transport mutants failed to colonize the intestines and failed to cause diarrhea in the mice, whereas the wild-type strain was not cleared and elicited a diarrheal response. These data indicate that disruption of either the heme utilization or the vibriobactin uptake system reduces the ability of V. cholerae to cause disease. One of the heme utilization mutants, DHH1, was found to be defective also in utilization of vibriobactin and ferrichrome, mimicking the Escherichia coli TonB- phenotype. This mutant was the least virulent of the iron transport mutants tested. Transformation of DHH1 with the recombinant plasmid pHUT4 restored the abilities to use hemin, vibriobactin, and ferrichrome as iron sources, suggesting that pHUT4 encodes a gene(s) involved globally in the iron transport systems. Hybridization of Vibrio DNA with the V. cholerae heme utilization genes demonstrated the presence of DNA homologous to the genes encoding the outer membrane protein HutA and the inner membrane protein HutB in all the V. cholerae strains tested. The probe containing hutA, but not that containing hutB, also hybridized to DNA from Vibrio parahaemolyticus.