Riboswitch controls bacterial migration

Chemotactic bacteria can be reprogrammed to respond to particular small molecules and thus navigate their surroundings, according to a report by Justin P. Gallivan and Shana Topp of Emory University (J. Am. Chem. Soc., DOI: 10.1021/ja0692480). Such bacteria could be used in bioremediation and drug delivery, they say. The researchers controlled the chemical-induced movement of the bacteria, or chemotaxis, by adding a theophylline-binding riboswitch to Escherichia coli that controls the expression of a key protein called CheZ. This protein is needed for the bacterium's flagellar motor to rotate properly; without it, the bacterium can't swim smoothly. In the reprogrammed cells, CheZ is produced only when the riboswitch binds theophylline. The riboswitch is specific enough that it doesn't bind caffeine, which is structurally similar to theophylline. The bacteria migrate as a function of theophylline concentration, heading toward areas of higher concentration. Even in the presence of natural bacterial chemoattractants, such as aspartate, the reprogrammed cells respond to aspartate only if theophylline also is present.