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.