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THE bacterium blamed for the Black Death that swept through medieval Europe,
now feared as a potential biological weapon, has had its genes sequenced. Julian
Parkhill of the Sanger Centre in Cambridge says the results show Yersinia
pestis is a relative newcomer. It evolved from a bug that causes mild gut
upset, by acquiring bacterial and viral genes that allow it to live in flea guts
and human blood (Nature, vol 413, p 523).