A PCR-based screening method was used to study the genetic variations of the
pgm locus among natural isolates of
Yersinia pestis from China. Our results indicate that genetic variations in the
pgm locus are well correlated with biovars of
Y. pestis and plague foci, suggesting that the
pgm locus plays a role in
Y. pestis adaptation to its environment. The gene encoding two-component regulatory system sensor kinase became a pseudogene in all strains of biovar
Orientalis due to a thymidine deletion, while it is intact in all the strains of the other biovars. Only strains from Foci H and L are the same as
Yersinia pseudotuberculosis in that they have an intact transmembrane helix in the sensor kinase protein, which is lost in all the other strains because of the 18 bp in-frame deletion. The IS
100 element that flanks the 3′ terminus of the
pgm locus was inserted into the chromosome during the within-species microevolution of
Y. pestis, which is absent in strains from Foci G, H and L and also in
Y. pseudotuberculosis. This fact indicates that the strains from these three foci are of an older lineage of Chinese
Y. pestis. It is this IS
100 element's absence that maintained high stability of the
pgm locus in the
Y. pestis strains from these three foci. The IS
285 element insertion in the pigmentation segment and the IS
100 element insertion in the downstream flanking region of the
pgm locus are only present in strains from Foci H and L. The flanking region outside the 5′ terminus of the upstream IS
100 element is identical in the strains from these two foci, which is different in the other strains. All of these unique characteristics suggest that they are of a special lineage of Chinese
Y. pestis.
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