Surprising Findings: Bacteria Punish Cheaters and Enforce Fairness Within Their Communities

Clostridium difficile Bacteria

The extreme steps these microorganisms would take to punish cheater species surprised the researchers.

A study reveals that bacteria can behave “spitefully.”

Annoyed by freeloaders? You are not alone, and taking advantage of others is an issue that affects all species, not just humans. In fact, such selfish behavior is not uncommon in the animal realm, where even cheater species of bacteria display it.

An even more intriguing fact was revealed by a York University-led study team that investigated bacteria’s quorum-sensing trait, a complex type of cooperation that allows bacteria to regulate gene expression based on population density.

Researchers from Case Western Reserve University and York University collaborated on the research, which was recently published in the journal PLOS Computational Biology. They were astonished to learn that bacterial colonies can go to the point of harming themselves in order to get rid of freeloaders.

“We didn’t expect to see this behavior, which you might even call ‘spiteful’,” says Associate Professor Andrew Eckford of York U’s Lassonde School of Engineering, and the study’s senior author. “But it indicates that quorum sensing is a remarkably flexible tool for enforcing fairness.”

In the study, scientists investigated how quorum sensing regulates the supply of shared resources, such as the enzymes that convert food sources into helpful nutrients. When freeloaders steal nutrients without creating enzymes, they discovered that the cheaters can be penalized even if the whole community suffers – similar to canceling a feast when an unwanted visitor sneaks in. Additionally, quorum sensing may starve the whole community if freeloading is widespread and no other food is available.

“It’s costly for a bacterium to contribute to the community, so for a selfish individual, it’s best to simply take what’s offered without giving anything back,” explains lead author Alex Moffett, who was a York U postdoctoral fellow at the time of the study. “But obviously this is bad for everyone, so the community needs a way to discourage bad behavior.”

Moffett and his colleagues found that instead of relying on the honor system, these microorganisms used quorum sensing to suppress the freeloaders. To further understand how quorum sensing compares to other strategies for controlling the production of public goods, they used mathematical modeling.

“Our model captures both how likely ‘cheater’ strains – which do not produce public goods but benefit from them – are to take over a population and how long on average the population will last before going extinct,” says co-author Peter J Thomas, professor of mathematics, applied mathematics and statistics at Case Western Reserve University, Cleveland, Ohio.

As quorum sensing plays an important role in bacterial infections such as the lung infections that affect sufferers of cystic fibrosis, the research team hopes to apply the results of this study to understand and disrupt such diseases. “This will help us understand how bacteria can colonize the lungs so effectively, which might point the way to new treatments,” adds Moffett.

Reference: “Cheater suppression and stochastic clearance through quorum sensing” by Alexander S. Moffett, Peter J. Thomas, Michael Hinczewski and Andrew W. Eckford, 28 July 2022, PLOS Computational Biology.
DOI: 10.1371/journal.pcbi.1010292

The study was funded by the Natural Sciences and Engineering Research Council of Canada, the United States Defense Advanced Research Projects Agency, and the National Science Foundation.

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