SIDEROPHORE PESTIBACTIN – AN IRON-DEPENDENT REGULATOR OF THE PLAGUE AGENT PATHOGENIC PROPERTIES

Siderophore-assisted iron assimilation is an important trait of pathogenic bacteria. The absence or reduction of production of such low-molecular-weight iron chelators dramatically lowers microbial potential to replicate in mammalian host. Earlier, we discovered a low-molecular-weight component – a siderophore secretion inhibitor (SSI) – capable of downmodulating siderophores production in plague pathogen cells by blocking their release into the environment. SSI was found in the autoagglutination factor (AF) purified from attenuated Yersinia pestis strains bearing chromosomal pgm locus deletion. The present study was aimed to isolate and characterize SSI, as well as to analyze its effects on Y. pestis bacteria and mammalian hosts. The SSI preparation was obtained from AF preparation purified from Y. pestis strain that lacks the biosynthesis genes for the two siderophores in the plague agent (yersiniabactin and yersiniachelin). Analyzing the physical and chemical properties of the preparation using gel electrophoresis, thin-layer chromatography, high-performance liquid chromatography, and mass spectrometry revealed that SSI is an iron-containing hydrophobic, fluorescent substance. Removal of iron from SSI preparation by extraction with 8-hydroxyquinoline resulted in emerging siderophore activity on the indicator medium used to detect siderophores in various bacterial species. Because SSI was obtained from a bacterial strain not synthesizing yersiniabactin and yersiniachelin allowed to considered it as an iron-bound third siderophore of the plague pathogen, which we named pestibactin (Pbt). Assessing Pbt functional properties revealed its multidirectional effect on Y. pestis bacteria. Depending on the absence (desferri-Pbt) or presence (ferri-Pbt) of iron, this siderophore either activated or inhibited not only siderophores secretion, but also Y. pestis properties such as autoagglutination and pigment absorption. The ferri-Pbt affected not only bacteria, but also the laboratory animals: mice inoculated with ferri-Pbt via intraperitoneal route showed that ferri-Pbt may attract neutrophils to the site of injection. Moreover, mice infected with highly virulent Y. pestis 231 strain added with ferri-Pbt reduced bacterial potential to cause lethal infection. In contrast to ferri-Pbt, desferri-Pbt had no effect on neutrophil chemotaxis and Y. pestis virulence. The study data suggest that Y. pestis Pbt siderophore acts as an iron-dependent regulator of the pathogenic properties of the plague pathogen modulating both bacteria and host phagocytes.