Bacterial cell-to-cell communication: sorry, can't talk now - gone to lunch!

The identification of novel bacterial cell-to-cell communication (quorum sensing) systems based on diffusible signal molecules, such as indole and the LuxS autoinducer-2, requires discrimination between true signalling molecules and metabolites present in culture supernatants. This depends on rigorous chemical characterisation and demonstration that the molecule controls cellular responses beyond those required to metabolise or detoxify the signal.