快猫短视频

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鈥檚 population in the 14th century (快猫短视频, 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 the transformation from a mild, food and water-borne disease to a lethal, flea-borne one was the acquisition of a single gene that allowed the bacterium to survive in the midgut of a flea.

The gene in question codes for an enzyme known as plasmid-encoded phospholipase D (PLD). Earlier work showed that this gene was picked up from another organism through a routine gene transfer. Hinnebusch鈥檚 group infected fleas with different variants of Y. pestis, only some of which had the PLD gene. They found that without it, the bacterium died in the flea鈥檚 gut. Exactly how the gene protects the bacterium is still unclear.

Once it could survive in the flea鈥檚 gut, the bacterium began to rely on fleas for its transmission. 鈥淵. pestis has lost its ability to survive in the outside environment,鈥� says Hinnebusch.

The new reliance on the rat flea may also have boosted the bacterium鈥檚 virulence, the team speculates. 鈥淭hat route of transmission may have favoured strains of Y. pestis that would produce significant bloodstream infection,鈥� says Hinnebusch.