Summary auto-generated
This study examined the role of the haemin storage (Hms) system in Yersinia pestis virulence. The Hms phenotype enables bacteria to form colored colonies on haemin and Congo Red agar at 26°C but not 37°C, accumulating significant quantities of haemin and iron in outer membranes at low temperature. Researchers tested whether adsorbed haemin and iron serve as nutritional sources, protect against reactive oxygen species, enhance cell adherence, or affect virulence. Results showed that iron and haemin stored by the Hms system were not efficiently mobilized for nutritional use during subsequent iron starvation at 37°C. In resistance assays, Hms-positive cells showed variable protection against hydrogen peroxide, superoxide, and nitric oxide depending on conditions. The Hms phenotype enhanced bacterial adherence to HeLa cells and human neutrophils but did not provide protection against neutrophil killing. Notably, virulence testing in subcutaneously infected mice demonstrated that Hms-negative strains were slightly more virulent than Hms-positive strains, indicating the Hms phenotype is not essential for bubonic plague pathogenesis in mammals.
Key findings
- The haemin and iron adsorbed by the Hms system at 26°C were not utilized as nutritional sources during subsequent iron-restricted growth at 37°C
- The Hms phenotype provided only modest and variable protection against reactive oxygen species (H2O2, superoxide, nitric oxide) in vitro
- Hms-positive cells showed increased adherence to host cells (HeLa cells and neutrophils) compared to Hms-negative cells, but this did not confer resistance to neutrophil killing
- Hms-negative Y. pestis strains were slightly more virulent than Hms-positive strains in mouse subcutaneous infection models
- The hmsHFRS locus does not encode a functional haemin utilization system for iron or porphyrin acquisition
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Abstract
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 degrees 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 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 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.