Living systems operate far from thermodynamic equilibrium, which usually manifests as broken detailed balance at the molecular scale. At larger scales with collective function of many molecules, the presence of non-equilibrium thermodynamics may not be evident. In bacterial motility, the switching dynamics of the flagellar rotary motor was recently discovered to be operating in non-equilibrium. However, the resulting motility pattern at the mesoscale, the run-and-tumble behavior, was normally considered to be a Poisson process that can be described by a two-state equilibrium model. Here, we studied the details of the run-and-tumble behavior by following the polymorphic transformation of the flagellar filaments, observing broken detailed balance that reveals its non-equilibrium nature. Evaluation of entropy production provided a direct measure of the lack of detailed balance and a quantification of the rate of energy dissipation for bacterial run-and-tumble regulation.

生命系统的运行远离热力学平衡，这通常表现为分子尺度上详细平衡的破坏。在具有许多分子集体功能的更大尺度上，非平衡热力学的存在可能并不明显。在细菌运动中，最近发现鞭毛旋转马达的切换动力学在非平衡状态下运行。然而，由此产生的中尺度运动模式，即运行和翻滚行为，通常被认为是泊松过程，可以用二态平衡模型来描述。在这里，我们通过跟踪鞭毛丝的多态性转化来研究奔跑和翻滚行为的细节，观察打破的细节平衡，揭示其非平衡本质。