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Not so different after all

A tiny change in plague’s genetic code may make it deadlier than its innocuous relative

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5:23pm, May 5, 2008

Bubonic plague may be deadlier than its benign cousin because of two small tweaks to its genetic blueprint, new research suggests.

The bubonic plague bacterium, Yersinia pestis, has killed more than 200 million people, while its ancestor Yersinia pseudotuberculosis is usually harmless. The two diverged a mere 20,000 years ago, implying that only a few genetic changes made Y. pestis lethal, says Ronald Viola, a chemistry professor at the University of Toledo in Ohio. Researchers also noticed that harmful species of the genus Yersinia made nonfunctional versions of an enzyme called aspartase, while less infectious Yersiniae created functional forms. Aspartase breaks down the amino acid aspartic acid.

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