Insights from Genomics into Bacterial Pathogen Populations
Bos, Schuenemann, and colleagues  combined ancient DNA techniques with whole genome sequencing to reconstruct a draft genome of Yersinia pestis, the bacterium responsible for the Black Death, from five teeth recovered from a 660-year-old burial ground. (A) Genealogical reconstruction reveals that the bacteria responsible for the Black Death are positioned ancestral to modern Branch 1 Yersinia pestis, close to the most recent common ancestor of all modern Yersinia pestis pathogenic to humans. No derived mutations were observed in the ancient genome, suggesting that modern Branch 1 bacteria are essentially equivalent, and that differences in modern and 14th century epidemiology probably do not result from genetic changes in the bacteria. (B) Geographical origin of the bacterial isolates. (C) Inferred geographical spread of the Black Death through Europe . Reproduced from  appearing in Nature (Volume 478, 2011).