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The secretion of Yops via the type III secretion system (T3SS) is controlled, in part, by a cytoplasmic YopN/TyeA complex. This complex is required to prevent Yop secretion in the presence of extracellular calcium and prior to contact between the bacterium and a eukaryotic cell. In this study we utilized site-directed mutagenesis to analyze the role of specific TyeA regions and residues in the regulation of Yop secretion. We identified two spatially distinct, surface-exposed regions of the TyeA molecule that were required to regulate Yop secretion. One region, identified by residues M51, F55 and P56, was required for TyeA to interact with YopN. A second region, identified by residues R19, W20 and D25 was not involved in the interaction of TyeA with YopN, but may be required for the YopN/TyeA complex to interact with the T3S apparatus in a manner that blocks Yop secretion.

Many members of the genus encode homologues of insect toxins first observed in bacteria that are insect pathogens such as , and . These bacteria secrete high molecular weight insecticidal toxins comprised of multiple protein subunits, termed the Toxin Complexes or Tc’s. In three distinct Tc subunits are required for full oral toxicity in insects, that include the [A], [B] and [C] types, although the exact stochiometry remains unclear. The genomes of strains encode multiple loci, although only two have been shown to exhibit oral and injectable activity against the Hawk Moth, . The exact role of the remaining homologues is unclear. The availability of bacterial genome sequences has revealed the presence of gene homologues in many different species. In this chapter we review the gene homologues in genus. We discuss what is known about the activity of the Tc protein homologues and attempt to relate this to the evolution of the genus and of the gene family

Bacteria utilise Twin arginine translocation (Tat) to deliver folded proteins across the cytoplasmic membrane. Disruption of Tat typically results in pleiotropic effects on e.g. growth, stress resistance, bacterial membrane biogenesis, motility and cell morphology. Further, Tat is coupled to virulence in a range of pathogenic bacteria, including species of , , and . We have investigated this, for , previously unexplored system, and have shown that the Tat pathway is functional and absolutely required for virulence of . A range of putative Tat substrates have been predicted , which together with the Tat system itself may be interesting targets for future development of antimicrobial treatments. Here we present a brief review of bacterial Tat and discuss our results concerning this system in

The Pla surface protease of , encoded by the specific plasmid pPCP1, is a versatile virulence factor. In vivo studies have shown that Pla is essential in the establishment of bubonic plague, and in vitro studies have demonstrated various putative virulence functions for the Pla molecule. Pla is a surface protease of the omptin family, and its proteolytic targets include the abundant, circulating human zymogen plasminogen, which is activated by Pla to the serine protease plasmin. Plasmin is important in cell migration, and Pla also proteolytically inactivates the main circulating inhibitor of plasmin, α2-antiplasmin. Pla also is an adhesin with affinity for laminin, a major glycoprotein of mammalian basement membranes, which is degraded by plasmin but not by Pla. Together, these functions create uncontrolled plasmin proteolysis targeted at tissue barriers. Other proteolytic targets for Pla include complement proteins.

is one of the most common causes of food borne gastrointestinal disease. After oral uptake yersiniae replicate in the small intestine, invade Peyeŕs patches of the distal ileum and disseminate to spleen and liver. In these tissues and organs yersiniae replicate extracellularly and form exclusively monoclonal microabscesses. Only very few yersiniae invade Peyeŕs patches and establish just a very few monoclonal microabscesses. This is due to both and host specific factors.

biovar 1B maintains two distinct and independently operating type 3 secretion (T3S) systems with the capacity to translocate toxic effector proteins into mammalian cells. Each of these T3S systems plays a role in the outcome of an infection by influencing different stages of infection. Recent investigations of the Ysa T3S system have revealed it is important for survival during the gastrointestinal phase of infection. This sets this system apart from the Ysc T3S system which is important for systemic infections. Identification of the effector proteins has provided insight on how the Ysa T3S system modulates interactions with the host. In part, the Ysa T3S system targets the innate immune response to suppress the ability of the host to rapidly clear an infection.

Pathogenic yersiniae either repress flagella expression under host conditions ( and ) or have permanently lost this capability by mutation (). The block in flagella synthesis for the enteropathogenic centers on (σF) repression. This repression ensures the downstream repression of flagellin structural genes which can be cross-recognized and secreted by virulence type III secretion systems. carries several flagellar mutations including a frame shift mutation in , part of the flagellar master control operon. Repression of flagellins in the host environment may be critical because they are potent inducers of innate immunity. Artificial expression of flagellin in completely attenuates virulence, supporting the hypothesis that motility is a liability in the mammalian host.

YopP in and YopJ in , have been shown to exert a variety of adverse effects on cell signaling leading to suppression of cytokine expression and induction of programmed cell death. A comparative study with and O:8 virulent strains shows some critical disparity in YopJ/YopP-related effects on immune cells. Involvement of yopJ in virulence was evaluated in mouse model of bubonic plague.

Multiple copies of several classes of insertion sequences (IS) are found in the genome of pestis, the causative agent of bubonic and pneumonic plague. We used the genetic instability generated by these IS to develop a method (designated 3IS-RFLP) based on the restriction fragment length polymorphism of the IS, IS and IS elements for studying strains of worldwide origin. We show that 3IS-RFLP is a powerful tool to group isolates according to their geographical origin, and therefore that this method may be valuable for investigating the origin of new or re-emerging plague foci or for addressing forensic issues.

The precise nature of the pathogen having caused early plague pandemics is uncertain. Although is a likely candidate for all three plague pandemics, the very rare direct evidence that can be deduced from ancient DNA (aDNA) analysis is controversial. Moreover, which of the three biovars, Antiqua, Medievalis or Orientalis, was associated with these pandemics is still debated. There is a need for phylogenetic analysis performed on strains isolated from countries from which plague probably arose and is still endemic. In addition there exist technical difficulties inherent to aDNA investigations and a lack of appropriate genetic targets. The recently described CRISPRs (clustered regularly interspaced short palindromic repeats) may represent such a target. CRISPR loci consist of a succession of highly conserved regions separated by specific “spacers” usually of viral origin. To be of use, data describing the mechanisms of evolution and diversity of CRISPRs in , its closest neighbors, and other species which might contaminate ancient DNA, are necessary.