QUORUM SENSING – DO BACTERIA COORDINATE?

Quorum sensing is the ability to detect and respond to population density. Focusing on bacteria, quorum sensing is the mechanism by which bacteria regulate gene expression in accordance with population density by using signaling molecules.

This mechanism was first reported in 1970 by Kenneth Nealson, Terry Platt, and J. Woodland Hastings. They observed that marine bacterium Aliivibrio fischeri did not luminesce in freshly inoculated culture but only after the bacterial population had increased significantly.

Bacteria use quorum sensing to regulate certain gene expressions that, at the same time, will coordinate their behavior. There are some actions, like the creation of biofilm, that would be completely irrelevant unless there is a certain concentration of bacteria doing it at the same time. In a way, they are coordinating their actions based on population density. There are many processes regulated by quorum sensing apart from biofilm formation like virulence factor expression, motility, bioluminescence, etc.

The mechanism that regulates the quorum sensing is simple but clever. Bacteria slowly secrete a signaling molecule (autoinducer) that individually will have no action and will diffuse away. However, if there is a high density of bacteria secreting these molecules, the autoinducer concentration will exceed their threshold level triggering the activation or repression of specific genes.

Essential oils are receiving a growing interest as a possible non-toxic inhibitor of quorum sensing. It is still not known how they exactly inhibit the process but recent discoveries point to different modes of action:

the inhibition of autoinducer synthesis.the inhibition of autoinducer transport and/or secretion.the sequestration of autoinducer.the inhibition of targets of autoinducer receptor binding.

This is line of investigation is certainly promising and likely to expand our knowledge of essential oils and their mechanisms of action.