Title: 3D spatial exploration by E. coli echoes motor temporal variability,
Abstract: 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.