Molecular Characterization of the Hemin Uptake Locus ( hmu ) from Yersinia pestis and Analysis of hmu Mutants for Hemin and Hemoprotein Utilization

ABSTRACT Sequence analysis of the hemin uptake locus ( hmu ) of Yersinia pestis revealed five genes, hmuRSTUV , required for use of hemin and hemoproteins as iron sources. The translated gene products have homologies with proteins of the hemin transport genes of several gram-negative bacteria. Promoters were identified upstream of hmuP′R (p1) and upstream of hmuS (p2); p1, which contains a Fur box, is regulated by iron and Fur, while p2 exhibits weak, but constitutive, activity. HmuR, which has homology with TonB-dependent outer membrane (OM) receptors, is localized to the OM of Y. pestis and is required for utilizing hemin and all hemoproteins under iron-depleted conditions. The proposed ABC transporter, HmuTUV, is necessary for use of hemin, hemin-albumin, and myoglobin, but not hemoglobin, hemoglobin-haptoglobin, or heme-hemopexin, as iron sources. In the absence of HmuTUV, HmuS, a cytoplasmic protein, is involved in use of hemoglobin and heme-hemopexin. In mice, the 50% lethal doses of Y. pestis Δ hmuP′RSTUV mutants injected subcutaneously or retro-orbitally did not differ from that of the Hmu + parent strain. Thus, the hmu system is not essential for infection in mice via these routes. Growth studies showed that a Δ hmuP′RSTUV mutant could grow in iron-depleted medium containing high concentrations of hemoglobin, suggesting that an Hmu-independent, lower-affinity hemoglobin uptake system may exist.