Bacteria navigate on surfaces using a 'sense of touch'

 

Many disease-causing bacteria such as Pseudomonas aeruginosa crawl on surfaces through a walk-like motility known as "twitching." Nanometers-wide filaments called type IV pili are known to power twitching, but scientists ignore which sensory signals coordinate the microbes' movements.

 

Now, EPFL researchers have found that Pseudomonas bacteria use a mechanism similar to our sense of touch to navigate on surfaces. This study changes the way we think about motility in bacteria.

 

 

Scientists have known that cells from humans and other animals can direct themselves in the direction of stiffer or looser surfaces, but it was unclear whether bacteria could also guide their movement based on mechanical force. This is because most studies have focused on identifying mechanisms that guide bacteria to swim towards chemicals such as food, a phenomenon known as chemotaxis.

 

Research has focused on how bacteria sense and respond to mechanical forces. Previous studies showed that Pseudomonas' pilus works like a harpoon: after it extends and touches a surface, the pilus activates a molecular motor that retracts the filament, thus propelling the cell forward.

 

To understand what coordinates the pili motors, researchers looked at how individual Pseudomonas bacteria move on surfaces such as the bottom of a laboratory dish. The team suspected that a network of proteins called Chp system regulates 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.

 

By combining fluorescent tags with a microscopy technique that helps to look at single pili in living cells, the researchers found that one messenger protein activates the pili to extend, propelling the cell forward, whereas another protein inhibits the formation of pili at the front of the moving cell. The two opposing messengers aren't found in the same place within the cell.

 

When bacteria bump into an obstacle such as another cell, the inhibitor allows them to stop and change direction. The ability to sense the surrounding environment is useful when bacteria move as a group helps the microbes to all crawl forward in the same direction.

 

See:

 

Marco J. Kühn, Lorenzo Talà, Yuki F. Inclan, Ramiro Patino, Xavier Pierrat, Iscia Vos, Zainebe Al-Mayyah, Henriette Macmillan, Jose Negrete, Joanne N. Engel, Alexandre Persat. Mechanotaxis directs Pseudomonas aeruginosa twitching motility. Proceedings of the National Academy of Sciences, 2021; 118 (30): e2101759118 DOI: 10.1073/pnas.2101759118

 

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology Resources (http://www.pharmamicroresources.com/)