Bacteria navigate on surfaces using a 'sense of touch'

Date:
August 5, 2021
Source:
Ecole Polytechnique Fe'de'rale de Lausanne
Summary:
Researchers have characterized a mechanism that allows bacteria
to direct their movement in response to the mechanical properties
of the surfaces the microbes move on -- a finding that could help
fight certain pathogens.



FULL STORY ==========================================================================
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.


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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," says senior
author Alexandre Persat, a tenure track assistant professor at EPFL's
School of Life Sciences.

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, Persat says. That's because most studies have focused
on identifying mechanisms that guide bacteria to swim towards chemicals
such as food, a phenomenon known as chemotaxis.

Research in the Persat lab has instead 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 in the
Persat group and their collaborators at the University of California,
San Francisco, 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. "The activator localizes to the front,
where the cell feels the surface with its pili, while the inhibitor
localizes everywhere else," says study co-first author Marco Ku?hn.

When bacteria bump into an obstacle such as another cell, the inhibitor
allows them to stop and change direction, the researchers found. "This
helps the cells navigate based on what they feel in front of them -- like
a blind person using a white cane," Persat says. The ability to sense the surrounding environment is useful when bacteria move as a group, he adds,
as it helps the microbes to all crawl forward in the same direction.

The findings, published in PNAS, shed light on how bacteria move and could
have important implications for human health. Pseudomonas aeruginosa,
an opportunistic pathogen that is commonly found in soil, is a leading
cause of hospital-acquired infections. Aggregates of Pseudomonas bacteria typically form on surfaces such as catheters and respirators and can be extremely resistant to disinfectants and antimicrobial drugs.

What's more, past research from the Persat group showed that Pseudomonas
uses its pili to regulate the secretion of toxins. For this reason, understanding more about the microbes' "sense of touch" could help to
develop new therapeutic strategies, Persat says.

Next, the researchers aim to uncover how the bacteria convert a mechanical stimulus into a cellular response, says study co-first author Lorenzo
Tala`.

"We would like to understand the molecular mechanism behind the
[bacteria's] sense of touch," he says.

========================================================================== Story Source: Materials provided by
Ecole_Polytechnique_Fe'de'rale_de_Lausanne. Original written by Giorgia Guglielmi. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Marco J. Ku"hn, Lorenzo Tala`, 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 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210805140011.htm

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