Some Bacteria Grapple onto Surfaces Like Batman

Certain types of microorganisms use Batman-like grappling hooks to slingshot their way across surfaces. This allows them to move while consuming energy only in short bursts. Other species of bacteria have yet to master this technique.

Another common form of motion is a jerky approach called twitching motility. Bacteria using it move forward exactly as the name implies, by twitching across a surface until they reach a good position.

But some use type IV pili (TFP) to move forward. These are hair-like structures protruding out of a bacterium's shell. They work like grappling hooks, extending from the cell until they come across something they can hold onto.

After they are securely latched to a surface, these protrusions contract, pulling the entire cell forward. In this manner, a colony of bacteria can move forward with efficiency, before deciding to settle down and start constructing their dreaded biofilms.

Details of the new research effort have already been published online, in this week's issue of the esteemed journal Proceedings of the National Academy of Sciences (PNAS). The work was led by scientist Gerard Wong, from the University of California in Los Angeles (UCLA).

The expert holds an appointment as a professor of bioengineering and of chemistry and biochemistry at the UCLA Henry Samueli School of Engineering and Applied Science. He is also a member of the California NanoSystems Institute (CNSI) at the university.

During the investigations, the expert and his group were looking at Pseudomonas aeruginosa, a dangerous bacteria that is responsible for many death among humans, primarily from hospital-acquired infections. The team was studying twitching motility.

At one point, Wong and other experts observed that linear translational pulls of constant velocity alternated with velocity spikes as the bacterial cells moved. The spikes were u to 20 times faster, but lasted for only a few milliseconds.

“The constant velocity is due to the pulling by multiple TFP; the velocity spike is due to the release of a single TFP. The release action leads to a fast slingshot motion that actually turns the bacteria efficiently by allowing it to over-steer,” the team leader says.

In other words, P. aeruginosa is capable of literally slingshooting itself across surfaces. “If you look at the surfaces the bacteria have to move on, they are usually covered in goop. Bacterial cells secrete polysaccharides on surfaces, which are kind of like molasses,” Wong explains.

“Because these polysaccharides are long polymer molecules that can get entangled, these are very viscous and can potentially impede movement. However, if you move very fast in these polymer fluids, the viscosity becomes much lower compared to when you're moving slowly,” he adds.

“The fluid will then seem more like water than molasses. This kind of phenomenon is well known to chemical engineers and physicists,” the expert concludes.