The pigmentation (Pgm+) phenotype of Yersinia pestis, the causative agent of bubonic plague, originally referred to the ability of cells grown at 26 degrees C to adsorb (or store) sufficient exogenous hemin to form dark """"""""pigmented"""""""" colonies. Normally, avirulent, spontaneous Pgm- mutants require injected iron for conditional virulence. This result was the first indication that iron availability influenced the outcome of bacterial infections. It is now well established that mammalian iron- and hemin-binding proteins present invading pathogens with an iron-deficient environment. Pgm- mutants occur by deletion of 102 kb of chromosomal DNA which encodes at least two separate iron metabolism systems: iron-repressible outer membrane proteins IrpB-D which may be necessary for iron acquisition at 37 degrees C and the hemin-storage (Hms) system responsible for massive hemin-adsorption in the outer membrane at 26-30 degrees C but not 37 degrees C. The approximately 7-kb hms locus encodes at least two surface-exposed proteins (HmsF and HmsH) that exhibit approximately threefold higher expression at 26 degrees C than at 37 degrees C and a positive regulatory region (hmsR). HmsH expression requires exogenous hemin indicating that hemin binding by the system may have a physiological function. A mutation in hmsF abolishes hemin- regulation of HmsH while mutations in hmsH and hmsR perturb iron regulation or IrpB-D. Although the Hms system is not a hemin transport system it may affect iron metabolism in mammalian and flea environments. The investigators have recently used an E. coli mutant lacking high- affinity iron transport systems to clone iron acquisition systems from Y. pestis. One system (Hmu) allows the mutant to utilize hemin, myoglobin, hemoglobin, and hemoglobin-haptoglobin as iron sources. The goals of this project are to characterize the Y. pestis hemin-storage system and the Hmu hemin utilization system. The genetic organization of these loci will be determined by DNA sequencing and mutagenesis. Their genetic regulation will be examined via reporter gene fusions, RNA slot and Western blot analyses. The possible virulence role(s) of hemin storage will be tested in phagocytic cells, mice and fleas. The Hmu mechanism of hemin- compound utilization will be investigated and its role in the infectious process in mammals and fleas determined.
