Hunger for iron: the alternative siderophore iron scavenging systems in highly virulent Yersinia.

Low molecular weight siderophores are used by many living organisms to scavenge scarcely available ferric iron. Presence of at least a single siderophore-based iron acquisition system is usually acknowledged as a virulence-associated trait and a pre-requisite to become an efficient and successful pathogen. Currently, it is assumed that yersiniabactin (Ybt) is the solely functional endogenous siderophore iron uptake system in highly virulent Yersinia (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica biotype 1B). Genes responsible for biosynthesis, transport, and regulation of the yersiniabactin (ybt) production are clustered on a mobile genetic element, the High-Pathogenicity Island (HPI) that is responsible for broad dissemination of the ybt genes in Enterobacteriaceae. However, the ybt gene cluster is absent from nearly half of Y. pseudotuberculosis O3 isolates and epidemic Y. pseudotuberculosis O1 isolates responsible for the Far East Scarlet-like Fever. Several potential siderophore-mediated iron uptake gene clusters are documented in Yersinia genomes, however, neither of them have been proven to be functional. It has been suggested that at least two siderophores alternative to Ybt may operate in the highly virulent Yersinia pestis/Y. pseudotuberculosis group, and are referred to as pseudochelin (Pch) and yersiniachelin (Ych). Furthermore, most sporadic Y. pseudotuberculosis O1 strains possess gene clusters encoding all three iron scavenging systems. Thus, the Ybt system appears not to be the sole endogenous siderophore iron uptake system in the highly virulent yersiniae and may be efficiently substituted and/or supplemented by alternative iron siderophore scavenging systems.

Yersinia pestis autoagglutination factor is a component of the type six secretion system.

Autoagglutination (AA) is a protective phenotypic trait facilitating survival of bacteria in hostile environments and in the host during infection. Autoagglutination factors (AFs) that possess self-associating ability are currently characterized in many Gram-negative bacteria, but Yersinia pestis AFs are still a matter of debate. Previously, we have shown that AF of Hms(-) strain Y. pestis EV76 is a complex of the 17,485-kDa protein and a low-molecular-weight component with siderophore activity. Here, we identified the protein moiety of AF and examined its role in AA of Hms(+) and Hms(-)Y. pestis strains. Using MALDI-TOF MS of trypsin-hydrolyzed AF, we unambiguously identified the protein as YPO0502, which belongs to a family of Hcp-proteins forming pilus-like structures of the type six secretion system (T6SS). To address the role of YPO0502 in AA, we cloned ypo0502 in E. coli, overexpressed it in Y. pestis and constructed its knock-out mutant in Y. pestis. However, all these approaches failed: YPO0502 was not secreted in E. coli, formed inclusion bodies when overexpressed in Y. pestis, and could probably be compensated by other Hcp-like proteins in Y. pestis. In contrast, downregulation of ypo0502 expression by its antisense RNA supported the contribution of YPO0502 in AA of Hms(+) and Hms(-)Y. pestis strains. The results of the present study indicate that the Hcp-like component of T6SS encoded by ypo502 is involved in Y. pestis AA and suggest that at least one (ypo0499-0516) of the 6 T6SS clusters of Y. pestis is involved in bacterial interaction.