Carlo Giorgetti, University of Rome, La Sapienza

Red light-green light with bacteria: Time response in active turbulence

Dense bacterial suspensions exhibit collective behavior similar to inertial turbulence, even though the cells swim at an effective zero Reynolds number. Using light-driven bacteria, we study the onset of turbulence as a function of waiting time in dark, non-motile conditions. We find that “awakening” occurs on a characteristic time scale that is set by the waiting time. Furthermore, we show that the reawakened turbulent pattern can be strongly correlated with the past flow prior to light removal. This memory is only found for densities above a critical value, which is greater than that required for the onset of turbulence.