How do bacteria make decisions? Part 6: It takes a village

The marvels of single celled organisms is that they are able to integrate all kinds of stimuli and make one grand decision that affects how they proceed. Bacteria do in one cell what we as humans do with billions. However, do bacteria contain the ability to think as a group or community?

The answer is absolutely. It is called quorum sensing. The pioneer for this research is Bonnie Bassler from Princeton University. Listening to her tell her story of the curiosity she felt when observing how and why a certain group of bacteria emitted light, or bio-luminescence is great. (Watch here). Through her investigation with a insignificant bacterium, Vibrio harveyi, she opened up a whole new field of microbiology.

Many bacteria synthesize signaling molecules that serve as messages to other bacteria saying, “I am here”. Since bacteria don’t have senses that we are familiar with like sight and hearing, these signaling molecules tell other bacteria who is around. When there aren’t a lot of bacteria sending out the signal, no big decisions are made. However, when enough bacteria are around to tell all other village members the approximate population, all village members act together to make a committed decision. In the case of V. harveyi it is the production of a light emitting molecule, but for other bacterial species it may be activation of pathogenicity. From the perspective of the bacterium, you don’t want to decide alone to make a big commitment like invading another organism. By taking a bacterial census through quorum sensing, these bacteria make a educated decision only when their population is high enough to make an impact. For some species, this critical number may be less than ten. However, in some cases, the population needs to be in the millions.

I think bacteria can teach us a very important lesson via quorum sensing: don’t go it alone. It takes a village.

Azospirillum brasilense electron micrograph

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