The intracellular fate of
iron acquired by bacteria during
siderophore-mediated assimilation is poorly understood. We investigated this question in the pathogenic enterobacterium Erwinia chrysanthemi. This bacterium produces two
siderophores,
chrysobactin and
achromobactin, during plant
infection. We analyzed the distribution of
iron into cytosolic
proteins in bacterial cells supplied with 59Fe-chrysobactin using native gel electrophoresis. A parental strain and mutants deficient in
bacterioferritin (bfr), miniferritin (dps),
ferritin (ftnA), bacterioferredoxin (bfd), or
iron-
sulfur cluster assembly machinery (sufABCDSE) were studied. In the parental strain, we observed two rapidly 59Fe-labeled
protein signals identified as
bacterioferritin and an
iron pool associated to the
protein chain-elongation process. In the presence of increased 59Fe-chrysobactin concentrations, we detected mini-
ferritin-bound
iron.
Iron incorporation into
bacterioferritin was severely reduced in nonpolar sufA, sufB, sufD, sufS, and sufE mutants but not in a sufC background.
Iron recycling from
bacterioferritin did not occur in bfd and sufC mutants.
Iron depletion caused a loss of
aconitase activity, whereas ferric
chrysobactin supplementation stimulated the production of active
aconitase in parental cells and in bfr and bfd mutants.
Aconitase activity in sufA, sufB, sufD, sufS, and sufE mutant strains was 10 times lower than that in parental cells. In the sufC mutant, it was twice as low as that in the parental strain. Defects observed in the mutants were not caused by altered ferric
chrysobactin transport. Our data demonstrate a functional link between
bacterioferritin, bacterioferredoxin, and the Suf
protein machinery resulting in optimal bacterial growth and a balanced distribution of
iron between essential
metalloproteins.