Storage reservoirs of hemin and inorganic iron in Yersinia pestis

Abstract

It is established that a high-frequency chromosomal deletion of ca. 100 kb accounts for the loss of properties making up the pigmented phenotype (Pgm+) of wild-type Yersinia pestis. These determinants are known to include virulence by peripheral routes of injection, sensitivity to the bacteriocin pesticin, adsorption of exogenous hemin or Congo red at 26°C, and growth in iron-sequestered medium at 37°C. We have now identified the outer membrane as the primary site of exogenous hemin storage in Pgm+ cells grown at 26°C. Significant outer membrane storage of hemin did not occur in Pgm- mutants or in Pgm+ cells cultivated at 37°C. However, both Pgm+ and Pgm- organisms grown at 37°C contained a periplasmic reservoir of hemin, which may be associated with a temperature-dependent ca. 70-kDa peptide recently equated with antigen 5. At 37°C, Pgm+ and Pgm- yersiniae also utilized a cytoplasmic ca. 19-kDa bacterioferritin-like peptide for deposition of inorganic iron. Incorporation of [55Fe]hemin into pools at 37°C was not significantly inhibited by competition with excess unlabeled Fe3+. However, excess unlabeled hemin modestly competed with incorporation of label from 55FeCl3. This relative independence of storage pools observed at 37°C is consistent with physiological linkage to in vivo acquisition and transport of Fe3+ from ferritin and of hemin from hemoglobin, myoglobin, or hemopexin.