Configurational dynamics of flexible filaments in bacterial active baths

Abstract

Biopolymers with microscale length and nanoscale cross-sections subjected to active forces is a common non-equilibrium phenomenon in living creatures. It is therefore crucial to intuitively present and investigate the detailed dynamics of such flexible filaments in an active bath full of living matter. Hence, by introducing fluorescent actin filament into an active suspension of motile bacteria at different number densities in a quasi-two-dimensional chamber, we directly visualize the detailed interaction processes that bacteria deform a fluctuating filament by relative motion perpendicular to its principal axis of the filament and straighten a filament by parallel motions. We analyzed the evolution of bending energy in dilute and dense bacteria baths with gradual compact or coiled shapes. 
We successfully introduce a dimensionless number μ, named as active elasto-viscous number, which governs the generic deformation of filaments in the bacterial bath by comparing viscous force generated in bacterial active bath to elastic restoring force of filament.
The persistence length measuring the tangential correlation of the flexible filament is found to be proportional to μ. Finally, an effective temperature of the bacterial bath is given through the relation between constant stiffness and loading forces instead of popular used Einstein relation. Our findings provide detailed information and specific scaling of flexible filaments interplay with active forces and in response to living and crowded environments.

Anisotropic Diffusion of Elongated Particles in Active Coherent Flows

“…Recently, there have been experimental studies focusing on the dynamics of anisotropic passive particles in active flows [62][63][64][65][66][67]. In comparison to Brownian motion scenarios, it has been observed that, in active flows, particles exhibit anomalous coupled diffusion behavior, specifically diffusing preferentially along their minor axis.…”