Ferrioxamine transport mutants and the identification of the ferrioxamine receptor protein (FoxA) inErwinia herbicola (Enterobacter agglomerans)

Summary Iron deprivation ofErwinia herbicola (Enterobacter agglomerans) induces the biosynthesis of six high-M_r outer-membrane proteins and large amounts of ferrioxamine E. Mutagenesis withN-methyl-N-nitro-N-nitrosoguanidine and selection with ferrimycin A yielded mutants ofE. herbicola K4 (wild type), defective in the expression of a 76-kDa outer-membrane protein, as determined by SDS/polyacrylamide gel electrophoresis. While in bioassays wild-type cells showed growth promotion in the presence of ferrioxamines (B, D₁, D₂, E, G), enterobactin, citrate, ferrichrome and coprogen, these mutants failed to respond to ferrioxamines. Moreover, experiments with⁵⁵Fe-labelled siderophores confirmed that iron transport mediated by ferrioxamine E and B in the mutants was completely inhibited, whereas iron transport by other hydroxamate siderophores, such as ferrichrome and coprogen was unaffected. The results are evidence that the 76-kDa protein in the outer membrane represents the receptor protein (FoxA) for ferrioxamines inE. herbicola.