Acquisition of a gene that enables the plague bacterium to live inside bloodsucking fleas may have set the stage for the Black Death, a new study in the April 26 Science suggests. This plague epidemic killed an estimated 25 million people during medieval times.
"It's sobering to think about. An organism can pick up one or two [genes] and be capable of producing a new pandemic," says study coauthor B. Joseph Hinnebusch of the National Institute of Allergy and Infectious Diseases in Hamilton, Mont.
Discovered several decades ago in the plague bacterium, Yersinia pestis, the crucial gene encodes an enzyme that cleaves molecules known as phospholipids. The enzyme originally earned the name Yersinia murine toxin (Ymt) because extracts containing the molecule were