Emergence of <i>Escherichia coli</i> critically buckled motile helices under stress.

Abstract

Bacteria under external stress can reveal unexpected emergent phenotypes. We show that the intensely studied bacterium <i>Escherichia coli</i> can transform into long, highly motile helical filaments poized at a torsional buckling criticality when exposed to minimum inhibitory concentrations of several antibiotics. While the highly motile helices are physically either right- or left-handed, the motile helices always rotate with a right-handed angular velocity [Formula: see text], which points in the same direction as the translational velocity [Formula: see text] of the helix. Furthermore, these helical cells do not swim by a "run and tumble" but rather synchronously flip their spin [Formula: see text] and thus translational velocity-backing up rather than tumbling. By increasing the translational persistence length, these dynamics give rise to an effective diffusion coefficient up to 20 times that of a normal <i>E. coli</i> cell. Finally, we propose an evolutionary mechanism for this phenotype's emergence whereby the increased effective diffusivity provides a fitness advantage in allowing filamentous cells to more readily escape regions of high external stress.