Bacteria can use the sense of touch to steer on surfaces

Many bacteria such as Pseudomonas aeruginosa crawl on surfaces through walk-like motility known as "twitching". Twitching motility is a flagella-independent form of bacterial translocation over moist surfaces. It occurs by the extension and tethering powered by Nanometers-wide filaments called type IV pili, but scientists ignore which sensory signals coordinate the microbes’ movements.

Now, EPFL researchers have found that Pseudomonas bacteria use a mechanism that is close to our sense of touch to navigate on surfaces. "This study changes the way we think about motility in bacteria," says senior author Alexandre Persat. Prior to that, it was unclear whether bacteria could guide their movement based on mechanical force, Persat says. That's because most studies have focused on determining mechanisms that guide bacteria to swim towards chemicals such as food, a phenomenon known as chemotaxis.

Previous studies showed that after Pseudomonas' pilus extends and touches a surface, the pilus activates a molecular motor that retracts the filament, therefore pushing the cell forward. The team suspected that a network of proteins called the CHP system controls twitching, so they analyzed bacteria that lacked different components of the CHP system. Some of these mutant bacteria could barely move as they kept twitching back and forth; others always moved forward, even when they bumped into an obstacle.

The activator localizes to the front, where the cell feels the surface with its pili, while the inhibitor localizes everywhere else."

-Marco Kühn, Study Co-First Author

Accordingly, understanding more about the microbes' "sense of touch" could help evolve new therapeutic strategies, Persat says. "We would also like to understand the molecular mechanism behind the bacteria's sense of touch," he says.

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