After the Black Death reached London in 1348, about 2,400 people were buried in East Smithfield, near the Tower of London, in a cemetery that had been prepared for the plague’s arrival. From the teeth of four of those victims, researchers have now reconstructed the full DNA of a microbe that within five years felled one-third to one-half of the population of Western Europe.

The bacterium that causes plague, Yersinia pestis, is still highly virulent today but has different symptoms, leading some historians to doubt that it was the agent of the Black Death.

Those doubts were laid to rest last year by detection of the bacterium’s DNA in plague victims from mass graves across Europe. With the full genome now in hand, the researchers hope to recreate the microbe itself so as to understand what made the Black Death outbreak so deadly.

So far, the evidence points more toward the conditions of the time than to properties of the bacterium itself. The genome recovered from the East Smithfield victims is remarkably similar to that of the present-day bacterium, says the research team, led by Kirsten I. Bos of McMaster University in Ontario and Johannes Krause of the University of Tübingen in Germany.