The Mutant Genes Behind the Black Death

Research into the history of the plague reveals how the painstaking drudgery of lab work can eventually lead to amazing findings. Imagine spending a year separating the components of a bacterium and feeding the different parts to fleas to see what happens. That’s part of the work that went into mapping the history of mutations to the bacterium Yersinia pestis, which killed millions of people at a time during historical plague outbreaks.   

The most recent of these studies, published in June, found that the acquisition of a single gene named pla gave Y. pestis the ability to cause pneumonia, causing a form of plague so lethal that it kills essentially all of those infected who don’t receive antibiotics. In addition, it is also among the most infectious bacteria known. “Yersinia pestis is a pretty kick-ass pathogen,” said Paul Keim, a microbiologist at Northern Arizona University in Flagstaff. “A single bacterium can cause disease in mice. It’s hard to get much more virulent than that.”

The genetic makeover that led to the modern plague is thought to have occurred relatively recently in evolutionary history, anywhere from 1,500 to 20,000 years ago. But last month, a discovery was announced that could extend the history of the plague all the way back to a time before humans. George Poinar Jr., a biologist at Oregon State University in Corvallis, found that a 20-million-year-old flea encased in amber has a plague-like bacterium on its proboscis that could be an ancestor of Y. pestis. While a definitive identification of the bacterium hasn’t been made — and may not even be possible — an ancient ancestor of the Black Death could help reveal the earliest steps in a tortured evolutionary path, and perhaps help pinpoint at what point the most deadly changes occurred.

A change in a single gene -or even a part of a gene- at a time in Y. pestis allowed it to mutate at different points in history to do things like travel in fleas without killing them, cause pneumonia in humans, spread through the human body more efficiently, and spread from person to person. When all these factors were finally in place, we got pandemics. Read what we’ve learned about the evolutionary history of the plague at Quanta Magazine. -via Digg


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