Data from: Attenuation of virulence in Yersinia pestis across three plague pandemics

Yersinia pestis has spilled over from wild rodent reservoirs to commensal
rodents and humans causing three historically recorded pandemics.
Depletion in the copy number of the plasmid-encoded virulence gene pla
occurred in later-dated strains of the first and second pandemics, yet the
biological relevance of the pla deletion has been difficult to test. We
identified modern Y. pestis strains that independently acquired the same
pla depletion as ancient strains, and herein show that excision of pla
from the multi-copy pPCP1 plasmid is accompanied by the integration of a
separate full pPCP1 harboring pla into the single-copy pCD1
plasmid, reducing pla dosage. Moreover, we demonstrate that this depletion
decreases mortality of mice in models of bubonic plague, but not in the
pneumonic and septicemic forms of the disease. We hypothesize that pla
depletion may have been selectively advantageous in bubonic plague due to
rodent fragmentation following pandemic-induced mortality.