The Basics of Quorum Sensing
Off, and very close to the shallow shore of Hawaii there lives a marine animal known as the Hawaiian Bobtail Squid. This small squid does its hunting at night and on its back are detectors which cue the squid's body to light from the moon and the stars. So, the squid is aware of light. This squid does not produce a shadow as it swims because under the mantle of the squid are two glowing lobes. The glow of those lobes is caused by the generating of Bioluminescent Marine Bacteria, which having sensed that the population of themselves was of great number, they light up.
The symbiotic relationship of the Hawaiian Bobtail Squid and the Bioluminescent Marine Bacteria, or scientifically known as Vibrio fischeri is mutually beneficial. The bacteria are nourished within the body of the squid and the squid's lack of shadow at night as it hunts helps protect it from being detected by predators.
(The bacteria actually help ensure the squid lives longer and in this mutually beneficial situation, the squid also expels the bacteria before digging into the sand to sleep. Only a few of the bacteria are left and therefore, no light is made. So while bacteria can be extremely harmful, they can also be very helpful to the ecosystem and people also. We have bacteria in our stomachs which break down food for us.)
Bonnie Bassler, professor at Princeton says that these bacteria perceive when they are alone and when they are together and they do so communicating with chemicals, by emitting from themselves "auto inducers", or molecules. This is known as "quorum sensing" and it allows bacteria to communicate and jive their behavior to achieve a common goal. Individuality within bacteria colonies is not beneficial because they are so tiny. But when thousands or millions of them congregate, they can do much.
Autoinducer-2 is a family of signaling molecules used in quorum sensing. AI2 is produced by both Gram Negative and Gram Positive bacteria. In Gram Negative bacteria, at least 2 main classes of autoinducer have been defined. They are, AI1 and AI2. In Gram Positive bacteria, such as bacillus and enterococcus, autoinducers are usually short peptides.
It is a condition known as diffusion, which causes the autoinducer to be less developed when there are only a few bacteria in attendance with each other. Therefore, the bacteria don't begin communicating until more of their kind appear. The bacteria actually have the ability to count, in terms of understanding if their numbers are significant enough to begin a project. Like suppressing the immune system. This communication takes place once inside a host and is a superior tool for the success of the bacteria.
*Research is currently being done to find ways to confuse the bacterial communication system, in the interest of human health.
Sources: Bonnie Bassler/ibioseminars.org. Protein Data Bank TED.com