Pound-for-pound, it's the strongest organism ever. This mighty beast is the gonorrhea bacterium – the strongest creature alive.
These tiny creatures can pull with a force equal to 100,000 times their body weight – as though a human could drag 10 million kilos.
Many bacteria produce filaments called pili. These are a hundred times as long as they are wide and up to ten times longer than the bacterium itself. They can also contract. Scientists knew that Neisseria gonorhoeae bacteria use "type four" pili to crawl along a surface and to attach to cells and infect them.
What they didn't know was that these bacteria can bundle pili together to exert long, strong pulls. Michael Sheetz and colleagues at Columbia University in New York put the bacteria in a field of tiny gel "pillars" and measured the amount the bacteria could bend them as a way of measuring the force of their pull.
Short and long
They mostly saw a lot of short grabs. But one pull in a hundred started out at the same strength as these short pulls, then increased in increments about equal to the force of the original pull, as if the bacteria were calling in more individual pili to help out the first.
This eventually resulted in a pull that was up to ten times stronger than the initial short grab, and it could last for several hours.
Electron microscopic images confirmed the bundles. They also revealed that the reason scientists have not seen this before is because a protein usually added to bacterial culture medium happens to block it.
The actual force the bacteria exerted was around a nanoNewton, or one billionth of a Newton, the force you would need to accelerate a kilogram by a metre per second squared.
Not a lot – but it means the bacteria can pull with a force equivalent to 100,000 times its bodyweight, and hold it. This, say the authors, makes the retraction protein in the pili "the strongest biological motor known to date".
"This constitutes a new paradigm for the generation of forces in the biological realm," Sheetz and colleagues say, and could completely change our understanding of the way gonorrhea bacteria muscle up to cells and infect them.