Genetic analysis confirms Black Death caused by plague bacterium
13 September 2011
Genetic analysis of medieval skeletons of victims of the
Black Death has proven the presence of the plague bacterium,
Yersinia pestis. A study conducted by the University of Tübingen
and McMaster University proves that the pathogen that causes plague
today has been around at least 600 years.
The Black Death claimed the lives of one third of Europeans in
just five years from 1348 to 1353. Until recently it was not certain
whether the bacterium Yersinia pestis, which is known to
cause the plague today, was responsible for that most deadly
outbreak of disease ever. Now, the University of Tübingen’s
Institute of Scientific Archaeology and McMaster University in
Canada have been able to confirm that Yersinia pestis was
behind the great plague.
Previous genetic tests indicating that the bacterium was present
in medieval samples had previously been dismissed as contaminated by
modern DNA or the DNA of bacteria in the soil. Above all, there was
doubt because the modern plague pathogen spreads much more slowly
and is less deadly than the medieval plague — even allowing for
The researchers have for the first time been able to decode a
circular genome important for explaining the virulence of Y.
pestis. It is called pPCP1 plasmid and comprises about 10,000
positions in the bacterium’s DNA. The sample was taken from
skeletons from a London plague cemetery. The working group in
Tübingen, led by Dr Johannes Krause used a new technique of
“molecular fishing”, which involves enriching plague DNA fragments
from tooth enamel and sequencing them using the latest technology.
In this way, the fragments were connected up into a long genome
sequence — which turned out to be identical to modern-day plague
pathogens. “That indicates that at least this part of the genetic
information has barely changed in the past 600 years,” says Johannes
The researchers were also able to show that the plague DNA from
the London cemetery was indeed medieval. To do that, they examined
damage to the DNA which only occurs in old DNA — therefore excluding
the possibility of modern contamination. “Without a doubt, the
plague pathogen known today as Y. pestis was also the cause
of the plague in the Middle Ages,” says Krause, who is well known
for his DNA sequencing of ancient hominin finds, which help trace
relationships between types of prehistoric man and modern humans.
Schueneman VJ et al. Fishing for ancient pathogens: Y. pestis
confirmed in victims of the Black Death via high-throughput
sequencing of the pPCP1 plasmid. Proc Natl.Acad.Sci.USA, 2011.