There are some things bacteria don’t like to do alone. Certain resource-intensive activities—like constructing a biofilm scaffold or releasing virulence factors—don’t make sense unless there are plenty of bacteria around to lighten the load. That’s where quorum sensing comes into play.
Quorum sensing operates as a kind of automatic bacterial census. Each individual cell releases a chemical signal that it’s also sensitive to. When this signal reaches a concentration in the surrounding environment that indicates a sizable bacterial head count, gene expression changes.
Researchers from Waterloo University recently co-opted the quorum-sensing machinery in their quest to turn a common soil bacteria—Clostridium sporogenes—into a cancer treatment that eats tumors from the inside out.
Read more: “When Did I Start Getting Cancer?”
“Bacteria spores enter the tumor, finding an environment where there are lots of nutrients and no oxygen, which this organism prefers, and so it starts eating those nutrients and growing in size,” Marc Aucoin, a chemical engineer, explained in a statement. “So, we are now colonizing that central space, and the bacterium is essentially ridding the body of the tumor.”
The problem with this approach is that C. sporogenes is an obligate anaerobe, meaning it can’t tolerate oxygen. While it might thrive in the oxygen-poor environment within a tumor, the oxygenated tissues at the outer edges would spell certain death.
To address this issue, researchers borrowed a gene from another microbe capable of tolerating oxygen. By attaching it to a quorum-sensing system they can ensure it doesn’t switch on until enough bacteria have reproduced within the tumor itself.
“Using synthetic biology, we built something like an electrical circuit, but instead of wires we used pieces of DNA,” applied mathematician Brian Ingalls said. “Each piece has its job. When assembled correctly, they form a system that works in a predictable way.”
They recently demonstrated this novel approach in a study published in ACS Synthetic Biology using a fluorescent protein as a reporting mechanism. Now that they know it works, the team has clinical trials in their sights.
One day, instead of cancer eating our bodies from the inside out, these genetically engineered microbes might return the favor. 
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Lead image: Alesia-Susie / Shutterstock
