In Bacillus anthracis the
siderophore petrobactin is vital for
iron acquisition and virulence. The
petrobactin-binding receptor FpuA is required for these processes. Here additional components of
petrobactin reacquisition are described. To identify these
proteins, mutants of candidate
permease and
ATPase genes were generated allowing for characterization of multiple
petrobactin ATP-binding cassette (ABC)-import systems. Either of two distinct
permeases, FpuB or FatCD, is required for
iron acquisition and play redundant roles in
petrobactin transport. A mutant strain lacking both
permeases, ΔfpuBΔfatCD, was incapable of using
petrobactin as an
iron source and exhibited attenuated virulence in a murine model of inhalational
anthrax infection.
ATPase mutants were generated in either of the
permease mutant backgrounds to identify the
ATPase(s) interacting with each individual
permease channel. Mutants lacking the FpuB
permease and FatE
ATPase (ΔfpuBΔfatE) and a mutant lacking the distinct
ATPases FpuC and FpuD generated in the ΔfatCD background (ΔfatCDΔfpuCΔfpuD) displayed phenotypic characteristics of a mutant deficient in
petrobactin import. A mutant lacking all three of the identified
ATPases (ΔfatEΔfpuCΔfpuD) exhibited the same growth defect in
iron-depleted conditions. Taken together, these results provide the first description of the
permease and
ATPase proteins required for the import of
petrobactin in B. anthracis.