The Concept

As a group of students from Wits University in Johannesburg, South Africa, we have set out to genetically reprogram the chemotactic behaviour of E. coli, through the use of synthetic riboswitches. This will enable bacteria to search a defined area for a particular ligand and return to a set location (the starting point), where they can report on their findings. As a proof of principle, we want to test the ability of the reprogrammed cells to locate atrazine/theophylline on a petri-dish, and return to the initial point of departure for reporting. To do this we have three constructs that will make the bacteria toggle between two states of chemotactic responsiveness to different substances.

The first construct, called Motility factor – Send, will allow the bacterium to chemotactically search the area of the petri-dish for atrazine. Upon finding the source of the atrazine, the bacteria will express a reporter protein.Once the source of the atrazine has been found by the bacterium, a atrazine-sensitive Toggle Switch construct will be activated. This will turn off the first construct, and turn on the third.The third construct is called Motility factor – Return. The activation of this construct and the deactivation of the Motility factor - Send will alter the chemotactic behaviour of the bacterium and make the bacterium chemotactically responsive to theophylline, instead of atrazine. The source of theophylline will be located at the initial point of departure. At this location, the cells that have returned can be detected via a second reporter protein. The presence of this protein will be indicative of the presence of atrazine in the area.

Potential Applications

This project could have important implications in the fields of medicine, mining and water treatment. One would be able to send a "bacterial-messenger" out to detect certain substances which can act as chemoattractants - such as disease biomarkers or elemental metals. Via chemotaxis, the messenger E.coli will be able to search an area and locate the source of the chemoattractant. It will then travel back to the starting point to report back on its findings. Based on the information provided by these "messenger bacteria", and through recording the time taken for the bacteria to return, a probability density map can be generated, from which the location of the chemoattractant source can be determined. A potential application in diagnostics could be the non-invasive detection and localisation of cancerous cells in the colon, for example.