Plague Causing Bacteria Yersinia Pestis Was Once Harmless

Examining the genetic evolution of the Yersinia Pestis, the bacteria that caused epidemics like the Black Death, researchers found that acquisition of just one gene turned it deadly from being harmless.

A team of researchers from Northwestern University's Feinberg School of Medicine examined the effect of ancestral strains of the bacteria in mouse models to find that the ancestral bacteria could colonize the lung but did not cause the deadly infection that pneumonic plague is.  This ability to infect the lung early on helped it find it new environments.

"Our findings demonstrate how Y. Pestis had the ability to cause a severe respiratory disease very early in its evolution. This research helps us better understand how bacteria can adapt to new host environments to cause disease by acquiring small bits of DNA," Wyndham Lathem, one of the study's authors said.

By acquiring the Pla gene, Y.Pestis turned from a bacterium that caused gastrointestinal infections to one that causes the pneumonic plague, which is fatal in most cases.

When the ancestral strains were modified in animal models, it caused an illness similar to pneumonic plague, suggesting that the bacterium did not need anything more than the Pla gene to turn deadly.

The study published in Nature Communications also suggests that variations of the Pla gene helped the bacteria infect lymph nodes to cause bubonic plague.