Genomogenesis of the Plague Bacteria Yersinia pestis as a Process of Mosaic Evolution

Abstract

The guiding methodological principle of the modern molecular genetic (MG) approach to the problem of speciation of the plague bacteria Yersinia pestis is the saltationist paradigm of horizontal gene transfer. The main speciation events include the insertion of two virulence plasmids specific to Y. pestis, pFra and pPst, into the genome of ancestral psychrophilic saprozoonotic pseudotuberculosis bacteria Y. pseudotuberculosis O:1b, as well as inactivation/deletion of genes that have lost their functions. An alternative ecological approach suggests the “Darwinian” mechanism of the plague bacterium genome formation in the temperature-continuous (5–37°C) environment, i.e., the Tarbagan marmot–marmot flea (Marmota sibirica–Oropsylla silantiewi) parasitic system, which demonstrates intermediate properties between the habitats of progenitor and derivative species. In accordance with the ecological scenario of the plague origin, the evolutionary fate of 18 well-studied plague bacterium genes and gene structures was interpreted. It was demonstrated that gradual transformation of the genome of the pseudotuberculosis bacterium into the genome of plague causative agent proceeded according to the principle of mosaic evolution and corresponded to three types of adaptation, i.e., inadaptation, pre-adaptation and neo-adaptation. The prospects for further development of the theory of plague origin are thought to be in the synthesis of MG and ecological approaches.