Genomes of dangerous bacteria exposed. (Biomedicine).

Last month, researchers unveiled the genome of-bacteria that cause severe food poisoning, typhoid fever, and the plague that devastated the Middle Ages.

In the Oct. 25 NATURE, investigators from Canada, England, Vietnam, Denmark, and the United States describe the full DNA sequence of two strains of Salmonella enterica. One of the strains infects millions of people worldwide and causes severe food poisoning that can be fatal. The other is responsible for typhoid fever, which kills an estimated 600,000 people every year. The many genetic differences between the two bacteria should explain why they cause dissimilar illnesses, say researchers. The genomic sequences may also suggest new drug targets or vaccine leads.

In the Oct. 4 NATURE, scientists from England describe the genetic blueprint of Yersinia pestis, the bacterium presumed responsible for the Black Death that slew 25 million people during the medieval epidemic.

"The genome sequence of Y. pestis reveals a pathogen that has undergone considerable genetic flux," Julian Parkhill of the Sanger Centre in Cambridge, England, and his colleagues conclude. A recent study indicated that the plague bacterium evolved out of a less dangerous germ, Yersinia pseudotuberculosis, within the past 20,000 years (SN: 11/27/99, p. 343). Supporting this view is evidence that the genome of Y. pestis contains up to 150 inactive genes that appear to be remnants of genes still used by Y. pseudotuberculosis. The plague bacterium also has novel genes that may enable it to reside in insects, whereas Y. pseudotuberculosis lacks those genes. People get the plague when they're bitten by fleas that have fed on infected rodents.

--J.T.