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

The haemin storage (Hms(+)) phenotype of Yersinia pestis enables this bacil lus to form greenish/brown or red colonies on haemin or Congo Red agar plat es, respectively, at 26 but not 37 degrees C. Escherichia coil strains that contain mutations in genes essential for siderophore biosynthesis, porphyr in generation and/or haemin transport remain unable to utilize exogenous ha emin as a nutritional iron or porphyrin source when transformed with the cl oned 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 i ron-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 cell s to these reactive oxygen species at 26 and/or 37 degrees 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 e ffects of neutrophils. Finally, LD50 analysis in subcutaneously infected mi ce showed that an Hms(-) strain was slightly more virulent than Hms(+), ind icating that the Hms phenotype is not essential for the pathogenesis of bub onic plague in mammals.