Outer membrane peptides ofYersinia pestis mediating siderophore-independent assimilation of iron

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Abstract
It is established that wild-type cells ofYersinia pestis absorb exogenous hemin or Congo red and thus grow as pigmented colonies at 26° C on media containing these chromatophores (Pgm+). Pgm+ isolates are known to possess a siderophore-independent mechanism of iron-transport (required for growth in iron-deficient medium) which is absent in avirulent Pgm− mutants. Production of the bacteriocin pesticin and linked invasins (Pst+) is an additional defined virulence factor of yersiniae; mutation of Pgm+,Pst− organisms to pesticin-resistance (Pstr) results in concomitant conversion to Pgm−. In this study, autoradiograms of two-dimensional gels of [35S]methionine-labeled outer membranes from Pgm− mutants were compared to those of the Pgm+,Pst+ or Pgm+,Pst− parent. An apparently single predominant peptide present in these preparations (> 10% of total membrane protein) existed as a family of iron-modifiable 17.9-kDa molecules focusing down to isoelectric points of about 4.6 and up to 5.89. Expression of eight detectable Pst+-specific peptides was not significantly influenced by exogenous iron. Pgm+ yersiniae constitutively produced pigmentation-specific peptide F and five iron-repressible peptides termed IrpA to IrpE. Typical spontaneous mutation to Pgm− resulted in loss of peptide F and IrpB-E. A rare Pgm+,Pstr mutant, selected on Congo red agar containing pesticin, also lost IrpB-E but retained peptide F. This isolate, like Pgm− mutants, failed to grow in iron-deficient medium. Regardless of phenotype, all yersiniae utilized hemin, hemopexin, myoglobin, hemoglobin, and ferritin, but not transferrin or lactoferrin, as sole sources of iron.