What's the News: Bacteria are known for sprouting spindly limbs and pulling themselves along surfaces like miniature octopi. But a new study shows that by tacking down one limb, pulling it till it's taut, and then letting go, bacteria can also use the limbs to slingshot themselves around. What's the Context:
The class of bacterial limbs used for movement by the gonorrhea bacterium, among others, are called type IV pili. They consist of thin, fibrous bundles of protein, and to pull themselves forward, bacteria extend the pilus in front of them, tack down the tip, and start to absorb the limb back into the body, gradually shortening it while slipping across the surface toward their anchor.
Bacteria use them to get around on surfaces and form densely packed bacterial colonies called biofilms, which allow them to withstand the effects of antibiotics. Scientists study bacterial locomotion in hopes of finding a weak spot they can use to interrupt biofilm formation.
How the Heck:
In this study, scientists were looking at the motion of Pseudomonas aerunginosa, which causes respiratory infections--specifically, they were curious about the furious twitching movements that punctuated the bacterium's easy amble across a surface. This behavior has been noticed in many different bacterial species, but how it works, and why they do it, had been a mystery.
Using a mathematical model they'd built, the scientists found that the twitching seems to be how a bacterium executes a sharp turn in its trajectory.
To get this effect, a bacterium lets loose one of their taut pili while others remain anchored. The resulting spasm (illustrated above), akin to a slingshot being released, turns out to be 20 times faster than the bacteria's usual pace and whips them around to face a new direction.
The Future Holds: The slingshot tactic works particularly well in the kind of environment where biofilms form, the team notes. Further research will look into how a well-placed monkey wrench in the works could keep bacteria from twitching their way into a film. Reference: Fan Jin, Jacinta C. Conrad, Maxsim L. Gibiansky, Gerard C. L. Wong. Bacteria use type-IV pili to slingshot on surfaces. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1105073108
Image credit: Jin et al, PNAS (via New Scientist