SUPA, School of Physics and Astronomy, University of Edinburgh, JCMB, Kings Buildings, Mayfield Road, Edinburgh EH9 3JZ, UK.
Rep Prog Phys. 2012 Apr;75(4):042601. doi: 10.1088/0034-4885/75/4/042601. Epub 2012 Mar 9.
Microbiology is the science of microbes, particularly bacteria. Many bacteria are motile: they are capable of self-propulsion. Among these, a significant class execute so-called run-and-tumble motion: they follow a fairly straight path for a certain distance, then abruptly change direction before repeating the process. This dynamics has something in common with Brownian motion (it is diffusive at large scales), and also something in contrast. Specifically, motility parameters such as the run speed and tumble rate depend on the local environment and hence can vary in space. When they do so, even if a steady state is reached, this is not generally invariant under time reversal: the principle of detailed balance, which restores the microscopic time-reversal symmetry of systems in thermal equilibrium, is mesoscopically absent in motile bacteria. This lack of detailed balance (allowed by the flux of chemical energy that drives motility) creates pitfalls for the unwary modeller. Here I review some statistical-mechanical models for bacterial motility, presenting them as a paradigm for exploring diffusion without detailed balance. I also discuss the extent to which statistical physics is useful in understanding real or potential microbiological experiments.
微生物学是研究微生物的科学，特别是细菌。许多细菌是能动的：它们能够自行推进。在这些细菌中，有一个重要的类别执行所谓的“跑与跌”运动：它们沿着相当直的路径行进一定的距离，然后突然改变方向，然后再重复这个过程。这种动力学与布朗运动（在大尺度上是扩散的）有一些共同之处，也有一些不同之处。具体来说，运动参数，如奔跑速度和跌转率取决于局部环境，因此在空间上会发生变化。即使达到了稳定状态，如果时间反转，这种变化通常不会不变：在热平衡系统中恢复微观时间反转对称性的详细平衡原理，在能动细菌中从微观上是不存在的。这种缺乏详细平衡（由驱动运动的化学能量通量所允许）为粗心的建模者带来了陷阱。在这里，我回顾了一些细菌运动的统计力学模型，将它们作为探索无详细平衡扩散的范例。我还讨论了统计物理学在理解真实或潜在微生物实验方面的有用程度。
