3D spatial exploration by E. coli echoes motor temporal variability.

Unraveling bacterial strategies for spatial exploration is crucial to understand the complexity of the organi- zation of life. Currently, a cornerstone for quantitative modeling of bacterial transport, is their run-and-tumble strategy to explore their environment. For Escherichia coli, the run time distribution was reported to follow a Poisson process with a single characteristic time related to the rotational switching of the flagellar motor. Direct measurements on flagellar motors show, on the contrary, heavy-tailed distributions of rotation times stemming from the intrinsic noise in the chemotactic mechanism. The crucial role of stochasticity on the chemotactic response has also been highlighted by recent modeling, suggesting its determinant influence on motility. In stark contrast with the accepted vision of run-and-tumble, here we report a large behavioral variability of wild-type E. coli, revealed in their three-dimensional trajectories. At short times, a broad distribution of run times is measured on a population and attributed to the slow fluctuations of a signaling protein triggering the flagellar motor reversal. Over long times, individual bacteria undergo significant changes in motility. We demonstrate that such a large distribution introduces measurement biases in most practical situations. These results reconcile the notorious conundrum between run time observations and motor switching statistics. We finally propose that statistical modeling of transport properties currently undertaken in the emerging framework of active matter studies should be reconsidered under the scope of this large variability of motility features.