The gram-negative enteric pathogen Vibrio cholerae requires iron for
growth. V. cholerae has multiple iron acquisition systems, including
utilization of heme and hemoglobin, synthesis and transport of the catechol
siderophore vibriobactin, and transport of several siderophores that it does
not itself make. One siderophore that V. cholerae transports, but does
not make, is enterobactin. Enterobactin transport requires TonB and is
independent of the vibriobactin receptor ViuA. In this study, two candidate
enterobactin receptor genes, irgA (VC0475) and vctA (VCA0232),
were identified by analysis of the V. cholerae genomic sequence. A
single mutation in either of these genes did not significantly impair
enterobactin utilization, but a strain defective in both genes did not use
enterobactin. When either irgA or vctA was supplied on a plasmid,
the ability of the irgA vctA double mutant to use enterobactin was
restored. This indicates that both VctA and IrgA transport enterobactin. We
also identify the genes vctPDGC, which are linked to vctA and
encode a periplasmic binding protein-dependent ABC transport system that
functions in the utilization of both enterobactin and vibriobactin
(VCA0227-0230). An irgA::TnphoA mutant strain, MBG40, was shown in a
previous study to be highly attenuated and to have a strong colonization
defect in an infant mouse model of V. cholerae infection (M. B.
Goldberg, V. J. DiRita, and S. B. Calderwood, Infect. Immun. 58:55-60, 1990).
In this work, a new irgA mutation was constructed, and this mutant
strain was not significantly impaired in its ability to compete with the
parental strain in infant mice and was not attenuated for virulence in an
assay of 50% lethal dose. These data indicate that the virulence defect in
MBG40 is not due to the loss of irgA function and that irgA is
unlikely to be an important virulence factor.