Virulence-associated plasmids from Yersinia enterocolitica and Yersinia pestis

Abstract

A 44-megadalton [Md] plasmid associated with virulence and Ca2+ dependence from Y. enterocolitica 8081 was compared at the molecular level with a 47-Md plasmid associated with Ca2+ dependence from Y. pestis EV76. The plasmids shared 55% DNA sequence homology distributed over .apprx. 80% of the plasmid genomes. One region in which the plasmids differed contained sequences concerned with essential plasmid functions. Mutants (45) of Y. pestis were isolated which had spontaneously acquired the ability to grow on Ca2+-free medium (Ca2+ independence). Of these mutants, 21 were cured of their 47-Md plasmid, whereas the remaining had either suffered a major deletion of the plasmid or had a 2.2-kilobase insertion located in 1 of 2 adjacent BamHI restriction fragments encompassing .apprx. 9 kilobases. The inserted sequence was found at numerous sites on the Y. pestis chromosome and on all 3 plasmids in the strain and may represent a Y. pestis insertion sequence element.