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Cambridge University Science Magazine
The two methods of bacterial communication exploited by the researchers were quorum sensing and gas-phase redox signalling. Quorum sensing is an interaction that occurs between cells in a colony, which can be tailored to produce a burst of fluorescence. Although this is a strong interaction within the immediate area, it relies on the propagation of chemical species that diffuse slowly, leading to loss and delay of the signal over longer distances. Gas-phase redox signalling is a comparatively faster communication method and is therefore suitable for use over a longer distance; however, this type of signal is weak and short-lived.

The group combined these two methods with great success. Quorum sensing was used to synchronise the fluorescence of cells within a colony, while gas-phase communication - involving the release and interaction of hydrogen peroxide - was established to rapidly synchronise all the colonies in an array of up to 12,000 colonies, some 2.4 centimetres in length. The colonies were effectively “bio-pixels” in the array, which functioned in a similar manner to a liquid crystal display.

Further engineering of the circuit enabled it to be used as an arsenic-detector. The researchers designed an ON/OFF detection system whereby the bio-pixels fluoresced in the presence of arsenic. Remarkably, they could also quantify the amount of the toxin present in an unknown sample by measuring the effect on fluorescence.

The main drawback to this method is the bulk and expense of the microscopy equipment required to observe the fluorescence. If these problems could be overcome, the researchers believe that their genetic circuit could be implemented in an inexpensive hand-held device for the detection of arsenic and other toxins. 

Written by Ruth E. Gilligan