Genetically Engineered Clock Powered by Quorum Sensing

Researchers at the University of San Diego have been working on the creation of a bacterial clock. Their system relies on the bacterial communication system known as quorum sensing. In nature, microorganisms such as E coli use pheromone-like molecules called autoinducers to communicate and monitor their population density. The researchers made use of the autoinducer AHL and three different engineered circuits using the LuxI promoter.

One circuit consists of the luxI promoter with the luxI gene downtream. The luxI gene product is involved in the synthesis of AHL, which when bound to luxR, which is constitutively produced, activates the lux I promoter. The other two circuits use the same promoter, but with GFP and aiia downstream. Aiia is a molecule that degrades AHL. When a limited number of cells are present, these promoters are not activated. The cells produce AHL naturally, but not enough to cause activation. When the population recahes a certain level, 'quorum', however, there is enough AHL present that all of the luxI promters are activated and there is a burst of GFP expression. This occurs until enough aiia is also produced that it can degrade all fo the AHL. With not enough AHL present, the luxI promoters are all turned off and the cycle can start again. The result of their system is that they have a population of bacteria that glow green at intervals, a type of visual genetically engineered clock. The researchers hope that this will eventually lead the way to genetic sensors able to pulse differently dependent on different environmental conditions such as the presence of certain toxins.

For more details, check out this article published in Nature :

http://www.nature.com/nature/journal/v463/n7279/pdf/nature08753.pdf

Emily