Two genetic changes turned the plague into a scourge.
The ancestor of the plague-causing bacterium Yersinia pestis causes mild stomach disease. Early in its evolution, Y. pestis acquired a single gene from other bacteria that allowed it to cause the deadly lung infections of pneumonic plague, scientists report June 30 in Nature Communications. Later, one mutation in this gene enabled Y. pestis to invade the lymph nodes and blood, creating the bubonic plague behind pandemics like the 14th century’s Black Death.
Microbiologist Wyndham Lathem and colleagues at Northwestern University Feinberg School of Medicine in Chicago tested different strains of Yersinia bacteria in mice to determine which genes were needed for the microbes’ deadly evolution. The results indicate that Y. pestis could cause pneumonic plague very early in its evolution, and that one mutation may have made the difference between isolated disease outbreaks and global epidemics.
Other adaptations also make Y. pestis suited to its deadly role, Lathem says, so further research will seek additional genetic differences that separate the bacterium from its microbial predecessors.