The bacteria that cause the plague have killed many people throughout history.Scientifically named Yersinia pestis, the bacteria enter human and animal bodies often through flea bites.

Although instances of the disease are not nearly as common today, it remains a dangerous threat. Researchers have thus been searching the bacteria cells’ inner workings for keys to their ability to cause disease.

Y. pestis causes bubonic plague, or “Black Death,” when it infects the lymph system. The gruesome process begins with the formation of “buboes,” swollen nodules at limb joints, and then progresses to darkly colored spots all over the body. If untreated, death typically results in less than a week.

One strain of the bacteria can also infect the lungs and cause pneumonic plague, which is even more virulent.

However, Y. pestis is very closely related to the common gut and soil bacteria Yersinia pseudotuberculosis, which can cause a mild intestinal infection, and to about 12 other species of Yersinia. Why is one strain so much more dangerous than the others?

Researchers, publishing in the Proceedings of the National Academy of Sciences, found that small RNA molecules may make the difference.2 These “sRNAs” regulate bacterial protein production according to complicated feedback networks.

The researchers found that the Y. pestis species was missing six sRNAs that Y. pseudotuberculosis possesses. Further, these six sRNAs regulate the production of proteins that help enable the bacteria to cause disease….

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