Interdependence of behavioural variability and response to small stimuli in bacteria

In his study of Brownian motion, Einstein realized that the same random molecular movements characterizing a substance at rest should affect, for example, the drag it opposes to a particle pushed through it. This was later generalized as the fluctuation–response theorem (FRT), but whether and how it may apply to biological systems, which operate far from equilibrium, has remained an open question. Based on the unmatched fine-scale measurements possible in the study of bacterial chemotaxis, it is now revealed that the FRT does apply in this case, and ways to dissect which features in the biochemical network couple its internal states with its responses to external stimuli are suggested.