Black Death DNA sequenced from fourteenth-century teeth

Posted by Emma Woollacott

An international team of scientists has sequenced the entire genome of the Black Death, extracted from skeletons more than 700 years old.

It's the first time scientists have been able to draft a reconstructed genome of any pathogen older than 100 years or so, and could lead to a better understanding of modern infectious diseases.

The team found that a specific variant of the Yersinia pestis bacterium was responsible for the plague that killed 50 million Europeans between 1347 and 1351.

"The genomic data show that this bacterial strain, or variant, is the ancestor of all modern plagues we have today worldwide. Every outbreak across the globe today stems from a descendant of the medieval plague," says Hendrik Poinar of McMaster University.

"With a better understanding of the evolution of this deadly pathogen, we are entering a new era of research into infectious disease."

The team analyzed skeletal remains from victims buried in the East Smithfield plague pits in London, located under what is now the Royal Mint.

By targeting promising specimens from the dental pulp of five bodies, they were able to extract, purify and enrich specifically for the pathogen's DNA.

Linking the 1349-1350 dates of the skeletal remains to the genomic data allowed the researchers to calculate the age of the ancestor of the Yersinia pestis that caused the medieval plague.

It turned out to date from sometime between the 12th and 13th centuries, indicating that earlier plagues such as the Justinian plague of the sixth century - once thought to have been caused by the same pathogen - was likely caused by another, yet to be determined.

The direct descendants of the Smithfield bubonic plague still exists, however, killing 2,000 people each year.

"We found that in 660 years of evolution as a human pathogen, there have been relatively few changes in the genome of the ancient organism, but those changes, however small, may or may not account for the noted increased virulence of the bug that ravaged Europe," says Poinar.

"The next step is to determine why this was so deadly."