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Emergence of Escherichia coli critically buckled motile helices under stress

Trung V. Phan,Ryan J. Morris,Ho Tat Lam,Phuson Hulamm,M. Black,J. Bos,R. Austin

Published 2018 in Proceedings of the National Academy of Sciences of the United States of America

ABSTRACT

Significance We have discovered an emergent mechanism by which Escherichia coli can escape high-stress regions, such as near-lethal concentrations of antibiotics, by forming long motile helical filaments that are poized at the critical shear buckling point: 2π twist rotations independent of the length of the filament. All filaments, independent of length, have the same twist, indicating that this is a highly evolved response. The helices do not tumble as nonstressed bacteria do but rather, over a period of tens of seconds, reverse direction. The result is that the persistence length of the filaments’ translational motion is much larger than in unstressed normal-size bacteria, giving filaments an extremely large effective diffusion coefficient, allowing the bacteria to escape high existential stress. Bacteria under external stress can reveal unexpected emergent phenotypes. We show that the intensely studied bacterium Escherichia coli 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 ω→, which points in the same direction as the translational velocity v→T of the helix. Furthermore, these helical cells do not swim by a “run and tumble” but rather synchronously flip their spin ω→ 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 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.

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