Billions of years before hominids sharpened sticks into stabbing weapons, bacteria invented spears. Specifically, they invented transforming spears—structures that could almost instantly unfold from flat, coiled ribbons into long, pointed cylinders. They use these weapons to wage war on other microbes. And now, scientists—descendants of those early stick-sharpening hominids—are planning to tweak these bacterial javelins, and deploy them as tools for research, medicine, and more.
The story of the spears starts in 1938, with an American biologist named Tracy Sonneborn and his favorite organism—a hairy, single-celled, slipper-shaped organism called Paramecium. Sonneborn discovered that some strains of Paramecium are exceptionally violent, and can kill their more sensitive peers by releasing small particles into their environment.
Those particles turned out to be domesticated bacteria called Caedibacter that live inside the killer strains. When they’re released into the environment, they get gobbled up by other paramecia and shunted into a storage compartment called the vacuole. That’s where they unleash their spears.
These weapons are proteins called ‘Type 51 refractile bodies,’ or R bodies for short. When the bacteria first produce them, they take the form of rolled-up ribbons. But in the acidic conditions on a paramecium’s vacuole, the ribbons extend from the inside, stretching out by almost 40 times and transforming into a long, tapered tube. “Imagine a paper yo-yo,” says Jessica Polka from Harvard Medical School.