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A SINGLE gene filched from another organism helped transform a minor stomach bug into plague, researchers in the US and Sweden have confirmed.

Bubonic plague, which is transmitted by flea bites, killed off about a third of Europe’s population in the 14th century (Â鶹´«Ã½, 24 November 2001, p 34). But close genetic relatives of Yersinia pestis, the bacterium behind plague, seldom cause more than a mild stomach upset and are spread through contaminated food and water.

Now a team led by Joseph Hinnebusch of the Rocky Mountain Laboratories in Hamilton, Montana, has shown that a key step in…