Bacteria are incredibly powerful. They digest food, help trees grow, break down nutrients, make certain types of marine life (such as the squid above) glow, and account for about 90% of the cells in the human body. And, of course, bacteria like Salmonella and Streptococcus can quickly and completely ravage someone’s health. However, individual bacteria are more or less helpless. When placed inside a relatively giant host, whether it be a squid or a human, they can only function properly in unified groups. Thus, it is absolutely crucial that they are able to communicate with each other – and they have an elegant way of doing so.
Bacteria talk to each other through a process called “quorum sensing.” In the usual macroscopic sense, a quorum is “the minimum number of members of an assembly or society that must be present at any of its meetings to make the proceedings of that meeting valid,” and on the bacterial level, it has the exact same meaning. Bacteria are able to sense whether or not there are enough of them present to succeed in their endeavor – whether to digest a hamburger or infect a wound – and will only proceed when they hit that minimum number of members.
This works through a signaling system. Each bacterium contains a protein (the orange circle in the diagram below) that produces signaling molecules (the red pentagons) that the bacterium secretes and a receptor (the blue circles) to receive identical signaling molecules from other bacteria. When the bacteria are at a low density, the signaling molecules rarely bind with the receptors, but when the density reaches that required level, the signaling molecules bind with the receptors, and the bacteria are activated together as one bustling army.
This communication system works on two levels. First of all, bacteria of one species must first be able to communicate with each other so they can work in harmony. To allow this, each bacterium has a receptor that is specifically designed to only accept signaling molecules from the same species. However, bacteria rarely are isolated by species, and they also need to be able to communicate with the other types of bacteria surrounding them. So, they have a second system of signals and receivers that works across all species of bacteria. This way bacteria can decide both whether or not there is enough of them to accomplish their task and whether or not a different species with more members present would be better suited to accomplish it.
Quorum sensing as it applies to all bacteria was only discovered about a decade ago, and scientists are trying to take advantage of the new insight into their communication patterns to help work against destructive bacteria. For example, instead of just killing them, which often leads to resistant versions of the bacteria, scientists have developed imposter signaling molecules that bind to the receptors and keep the actual signaling molecules from being received, preventing the bacteria from taking action. It’s easy to think of bacteria as nasty blobs that lie around and make people sick, but they’re really ultra-specialized forces for both good and evil with communication systems that require man’s most developed technology to intercept.
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