[Principles of speciation of the plague causative agent Yersinia pestis: gradualism or saltation?].

The saltation origin of the causative agent of the plague Yersinia pestis from the pseudotuberculosis microbe Y. pseudotuberculosis O:1b has been proclaimed in recent investigations on molecular genetics. The speciation process in this case is proposed to be connected with horizontal inclusion of exogenous genetic structures (such as specific plasmids pFra and pPst) into the genome of the ancestral form. The alternative "Darwinian" model of the gradual origin of the plague agent is proposed based on ecological factors. The comparison of two evolutionary scenarios, saltation and gradual, is performed; the latter seems more likely.