We're used to thinking of bacteria as almost lifeless blobs whose primary job is to reproduce. The reality is far different.
Bacteria communicate with one another using a language called quorum sensing. The discovery was made in typical fashion: pure serendipity.
Two scientists in the 1970s noticed that bacteria that glowed made light only when many bacteria of the same species were close together. The scientists hypothesized that the bacteria were producing a chemical called an autoinducer, and when enough bacteria were close together, the autoinducer concentration rose high enough to switch the light on.
"Bacteria constantly communicate and share surprisingly complex information about themselves and their environments—not only with one another, but also with other cells and organisms," according to Frontiers for Young Minds (FYM).
"Researchers from Waterloo University recently co-opted the quorum-sensing machinery in their quest to turn a common soil bacteria—Clostridium sporogenes (C. sporogenes)—into a cancer treatment that eats tumors from the inside out." writes Jake Currie in Nautilus.
C. sporogenes has two qualities that were made to order for fighting cancer tumors. First of all, it hates oxygen. Most bacteria need oxygen to survive, but C. sporogenes does not.
“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.”
Near-perfect symbiosis: The bacteria get to eat, and humans are rid of cancerous tumors.
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.”
Quorum sensing is the oldest system of communication yet discovered. "They have about 5,000 genes, and up to 600 of those genes are controlled by quorum sensing," write the authors in FYM. "This means that up to one fourth of the bacterial genome is like an orchestra that is conducted by quorum sensing."
Quorum sensing was the first communication method to develop on Earth. It is also the earliest social behavior seen on Earth. Bacteria are so tiny that they cannot do much by themselves. But when they use quorum sensing to send and receive information about how many bacteria are around them and about how related they are to each other, they are acting more like a multicellular organism.
It's believed by researchers that using quorum sensing to tell bacteria what to do, or, more accurately, point them in the right direction, is one of the most exciting developments in medicine. Clinical trials of the C. sporogenes approach to shrinking tumors will begin soon.
