Characterization of a hemin-storage locus of Yersinia pestis

The pigmentation phenotype (Pgm+) of Yersinia pestis refers to temperature-dependent storage of hemin as well as expression of a number of other physiological characteristics. Spontaneous mutation to a Pgm- phenotype occurs via a large chromosomal deletion event and results in the inability to express the Pgm+ characteristics. In this study, we have used transposon insertion mutants to define two regions of a hemin-storage (hms) locus. A clone (pHMS1) encompassing this locus reinstates expression of hemin storage (Hms+) in Y. pestis spontaneous Pgm- strains KIM and Kuma but not in Escherichia coli. Complementation analysis using subclones of pHMS1 in Y. pestis transposon mutants indicates that both regions (hmsA and hmsB), which are separated by about 4 kb of intervening DNA, are essential for expression of the Hms+ phenotype. The 9.1-kb insert of pHMS1 contains structural genes encoding 90-kDa, 72-kDa, and 37-kDa polypeptides. Two-dimensional gel electrophoresis analysis of cells from Pgm+, spontaneous Pgm-, and Hms- transposon strains, as well as a spontaneous Pgm- strain transformed with pHMS1, indicated that two families of surface-exposed polypeptides (of about 87 and 69-73 kDa) are associated with the Hms+ phenotype.