Emergence of E. coli Critically Buckled Motile Helices Under Antibiotic Stress

Bacteria under external stress can reveal unexpected emergent phenotypes. We show that the intensely studied bacterium E. coli can transform into long, highly motile
helical filaments poised 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 $\vec \omega$ which points in the same direction as the translational velocity $\vec v_{T}$ of the helix.
Furthermore, these helical cells do not swim by a ``run and tumble'' but rather rather synchronously flip their spin $\vec \omega$ and thus translational velocity \textemdash{} 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 E. coli 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.