The haemin storage (Hms+) phenotype of Yersinia pestis is not essential for the pathogenesis of bubonic plague in mammals

Abstract

Summary: The haemin storage (Hms⁺) phenotype of Yersinia pestis enables this bacillus to form greenish/brown or red colonies on haemin or Congo Red agar plates, respectively, at 26 but not 37 °C. Escherichia coli strains that contain mutations in genes essential for siderophore biosynthesis, porphyrin generation and/or haemin transport remain unable to utilize exogenous haemin as a nutritional iron or porphyrin source when transformed with the cloned Y. pestis hmsHFRS locus. Further physiological analysis of the Hms⁺phenotype of Y. pestis strain KIM6+ suggests that the haemin and inorganic iron stored by the Hms system was not used nutritionally under subsequent iron-deficient conditions. In vitro analysis of the bactericidal effects of hydrogen peroxide, superoxide and nitric oxide showed that Hms^-Y. pestis cells, in certain cases, were more susceptible than the Hms⁺parent cells to these reactive oxygen species at 26 and/or 37 °C. In adherence assays, a higher percentage of Hms⁺cells were associated with HeLa cells and normal human neutrophils, compared to Hms^-cells. However, the Hms⁺phenotype did not provide any additional protection against the killing effects of neutrophils. Finally, LD₅₀ analysis in subcutaneously infected mice showed that an Hms^-strain was slightly more virulent than Hms⁺, indicating that the Hms phenotype is not essential for the pathogenesis of bubonic plague in mammals.