Y pestis a Recently Emerged Clone of Y pseudotuberculosis

Given the radical differences in ecology and natural history between Y. pestis and Y. pseudotuberculosis, it is surprising that they are in fact very closely related subspecies (Bercovier et al. 1980; Ibrahim et al. 1993). Population genetics analyses indicate that fully virulent Y. pestis strains worldwide constitute a clonal group with eight genomic branches separated by minor sequence differences (Achtman et al. 2004). Based on these analyses, it was estimated that Y. pestis diverged from its Y. pseudotuberculosis ancestor only within the last 10,000-20,000 years (Achtman et al. 1999, 2004). Further comparative genomics analyses confirmed a high degree of genomic identity between the two species (Chain et al. 2004; Hinchliffe et al. 2003; Zhou et al. 2004). The close phylogenetic relationship of Y. pseudotuberculosis and Y. pestis implies that the change from a comparatively benign food- and waterborne enteric pathogen to a highly virulent, arthropod-borne systemic pathogen occurred quite recently in evolutionary terms and is based on relatively few genetic differences (Hinnebusch 1997; Lorange et al. 2005).

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