Pseudomonas aeruginosa (P.a.) are proof against most antibiotics and cause life-threatening infections of wounds or the lungs. The P.a. bacteria species has a complete arsenal of strategies for evading the immune system and infecting tissue. Researchers working with Prof. Dr. Winfried Römer and Dr. Carsten Schwan of the University of Freiburg and the Excellence Cluster CIBSS – Centre for Integrative Biological Signalling Studies – have identified a previously unknown, natural, defense mechanism that protects cells from Pseudomonas infection. The study has been published in Cell Reports.

Pseudomonas aeruginosa also enter cells in a targeted way

Surrounded by nutrients and undetected by the immune system, the inside of a cell is the best place for pathogenic bacteria to breed. Nevertheless, it was long thought that they existed outside of cells for probably the most part. “Within the meantime, it’s clear that the image is more complex and the bacteria goal the cells they penetrate,” explains Römer. With the help of live cell imaging microscopy, this may be observed within the laboratory. The bacteria take up close contact to the cell and make indentations in its membrane until they’re completely engulfed by it.

Pseudomonas triggers the denting of the cell’s membrane by binding the virulence factor LecA to sugar molecules on the membrane’s surface. Proteins that bind with sugars are common within the natural world and are also observed on other bacteria and viruses. The strong binding of the bacteria and host cells results in the cell membrane closing itself like a zipper across the bacteria – a process that Römer’s working group has been examining for quite a while.

“Now we have intentionally focused on the role septins play in Pseudomonas infection,” says Schwan, describing the target of the present study. “It’s known of other bacteria that they manipulate host cell septins and might exploit them to ease penetration. Yet at the identical time, septins can even encapsulate bacteria which have already penetrated and induce their liquidation, in order that they have an ambivalent function in infections,” Schwan continues. Septins are a part of the cytoskeleton and function a key structural element just like a modular scaffold that may be flexibly put together and brought apart. In addition they incessantly play a job precisely when curved membranes are involved.

The binding of LecA is sufficient to induce septin accumulation

Of their latest study, the researchers used human lung cells that they infected with Pseudomonas aeruginosa within the lab. They found the attachment of the bacteria led to septins gathering at the location inside a couple of seconds or minutes. If the bacteria did not penetrate, the buildup then dissolved again quickly. The researchers could also observe this effect when as an alternative of bacteria small polymer beads coated with LecA got to the cells. This showed that binding via LecA was enough to induce septin accumulation.

We expected that Pseudomonas wanted this accumulation of septins, and that it helped them during infection, just as with other sorts of bacteria.”

Dr. Carsten Schwan, University of Freiburg and the Excellence Cluster CIBSS – Centre for Integrative Biological Signalling Studies

As an alternative, they found that twice as many bacteria could penetrate when the researchers knocked down among the septins. “We were surprised by the outcomes at first, but now we’re considering it isn’t just an isolated case. It may very well be that septins also play a protective role with many other pathogens,” he concludes.

A basis for developing drugs to treat antibiotic-resistant bacteria

The researchers were in a position to measure the strength of the septin barrier in further experiments. To do that, they attached the minimal bacterial model to the cantilever of an atomic force microscope (AFM), which allows the tiniest of indentations and resistances on surfaces to be measured as force. The researchers discovered that the cell membrane was clearly more rigid locally when the polymer beads were coated with LecA and septin amassed.

“That is an infinite effect when you concentrate on that throughout the infection process, many various molecules are involved. For an intervention to have such great impact, you regularly must inhibit several aspects, because otherwise, compensations are made,” says Römer.

He continues, “That speaks strongly for septins really playing a big role in warding off infections here.” The researchers now intend to further their investigations of lectins and septins. Higher understanding of those proteins could aid find points of attack for drugs designed to forestall infection by antibiotic-resistant bacteria.

In regards to the Cluster of Excellence CIBSS

The Cluster of Excellence CIBSS – Centre for Integrative Biological Signalling Studies has the goal of gaining a comprehensive understanding of biological signaling processes across scales – from interactions between individual molecules and cells to processes in organs and whole organisms. Researchers use the knowledge thus gained to develop strategies for controlling signals in a targeted manner. These technologies enable them not only to realize insights in research but additionally to develop innovations in medicine and plant sciences.

Source:

Journal reference:

Aigal, S., et al. (2022) Septin barriers protect mammalian host cells against Pseudomonas aeruginosa invasion. Cell Reports. doi.org/10.1016/j.celrep.2022.111510.