A unique defence: bacteria lose their cell wall in the presence of viruses

Bacteria temporarily live without their cell wall if dangerous viruses are nearby. A remarkable feature, because the cell wall is a strong barrier against threats. However, the discovery has a logical explanation and could have a consequence for the fight against pathogenic bacteria, according to Véronique Ongenae, first author of the publication in Open biology.

Bacteria can live without cell membran for a time under stressful conditions, discovered the group of Dennis Claessen, professor at the Leiden Institute of Biology (IBL) in 2018. “But its objective was not yet clear. My role is to find this advantage, by as a PhD candidate in the research group,” says Ongenae. “Therefore, I also work with Streptomyces, which are the bacteria which we discovered could live without their cell wall.”

A chance discovery

Ongenae cultivated Streptomyces in a so-called hyperosmotic environment. It has a high concentration of glucose, allowing bacteria to shed their cell wall, instead of breaking apart. Ongenae: “I did crazy experiments to let bacteria lose their cell wall, and I wondered what would happen if I added bacteriophages to Streptomyces. These are viruses that infect bacteria. And immediately, all Streptomyces lose their cell wall. I couldn’t believe my so I repeated the experiment over and over again, but the result remained the same.”

With other known bacteria, such as Escherichia coli and Bacillus subtilis, Ongenae noted the same reaction to the presence of phages in a hyperosmotic environment. She suspects that bacteria shed their cell wall as soon as they are infected with the phage. “It’s something we’re looking at, but it feels like a defense mechanism,” Ongenae notes. “By losing their cell wall, the bacteria become unrecognizable to the phage and remain under the radar.”

Dangerous for humans

The interesting finding also reveals potential complications in treating infections. “Phage therapies are now more often used as a replacement for antibiotics, to rid the body of pathogenic bacteria. Especially since antibiotic resistance becomes more widespread, phage therapy can be seen as a new way to treat infections. But now it turns out that bacteria can hide from phages. And like our blood vessels and urine also form a hyperosmotic environment, bacteria can also live there without a cell wall. So when the phages leave the body after a few days, the bacteria push back their cell wall and bring the infection back.”

For this reason, Ongenae is also studying the effect on Pathogenic bacteria, such as Pseudomonas aeruginosa and Acinetobacter baumannii. “Only then will we know if it’s something to consider.”