Yersinia pestis YbtU and YbtT are involved in synthesis of the siderophoreyersiniabactin but have different effects on regulation

One prerequisite for the virulence of Yersinia pestis, causative agent of b ubonic plague, is the yersiniabactin (Ybt) siderophore-dependent iron trans port system that is encoded within a high-pathogenicity island (HPI) within the pgm locus of the Y. pestis chromosome. Several gene products within th e HPI have demonstrated functions in the synthesis or transport of Ybt. Her e we examine the roles of ybtU and ybtT. In-frame mutations in ybtT or ybtU yielded strains defective in siderophore production. Mutant strains were u nable to grow on iron-deficient media at 37 degrees C but could be cross-fe d by culture supernatants from a Ybt-producing strain of Y. pestis. The ybt U mutant failed to express four indicator Ybt proteins (HMWP1, HMWP2, YbtE, and Psn), a pattern similar to those for other ybt biosynthetic mutants. I n contrast, strains carrying mutations in ybtT or ybtS (a previously identi fied gene required for Ybt biosynthesis) produced all four proteins at wild -type levels under iron-deprived conditions. To assess the effects of ybtT, -U, and -S mutations on transcription of ybt genes, reporter plasmids with ybtP or psn promoters controlling lacZ expression were introduced into the se mutants. Normal iron-regulated beta-galactosidase activity was observed in the ybtT and ybtS mutants, whereas a significant loss of expression occu rred in the Delta ybtU strain. These results show that ybtT and ybtU genes are involved in the biosynthesis of the Ybt siderophore and that a ybtU mut ation but not ybtT or ybtS mutations affects transcription from the ybtP an d psn promoters.