The plague, caused by the bacteria Yersinia pestis, has struck humanity three times in history. It's surprising that some strains, like biovar microtus, don't affect humans as much. This bacteria has a clever trick up its sleeve. It can survive and grow inside the immune cells of warm-blooded animals. This is crucial for its early stages of infection.

A recent discovery shows that a tiny change in a gene called gppA helps the bacteria survive inside human immune cells. This gene makes an enzyme called GppA, which converts a molecule called pppGpp into ppGpp. The mutation in gppA is found in all modern Yersinia pestis strains that cause the plague. But the older microtus strains have a fully functional GppA.

This mutation might explain why microtus strains are less harmful to humans. When GppA is not working, the balance of ppGpp and pppGpp is disrupted. This leads to an increase in genes that help the bacteria make essential amino acids. These amino acids are vital for the bacteria's growth. This enhanced survival ability within immune cells could be a key factor in the bacteria's virulence towards humans.

The discovery of this molecular mechanism sheds light on how Yersinia pestis has evolved to be so dangerous to humans. Understanding this could help us predict and prevent new infectious diseases. It's fascinating to see how a small change in a gene can have such a big impact on a bacteria's ability to cause disease. This knowledge could be crucial in the fight against infectious diseases.

Plague Bacteria's Secret Weapon: How a Tiny Mutation Makes a Big Difference

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