Berg H C
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 1996 Dec 10;93(25):14225-8. doi: 10.1073/pnas.93.25.14225.
Descriptions are given of three kinds of symmetries encountered in studies of bacterial locomotion, and of the ways in which they are circumvented or broken. A bacterium swims at very low Reynolds number: it cannot propel itself using reciprocal motion (by moving through a sequence of shapes, first forward and then in reverse); cyclic motion is required. A common solution is rotation of a helical filament, either right- or left-handed. The flagellar rotary motor that drives each filament generates the same torque whether spinning clockwise or counterclockwise. This symmetry is broken by coupling to the filament. Finally, bacterial populations, grown in a nutrient medium from an inoculum placed at a single point, usually move outward in symmetric circular rings. Under certain conditions, the cells excrete a chemoattractant, and the rings break up into discrete aggregates that can display remarkable geometric order.
本文描述了在细菌运动研究中遇到的三种对称性，以及规避或打破这些对称性的方式。细菌在极低的雷诺数下游动：它无法通过往复运动（通过一系列形状变化，先向前然后向后移动）来推动自身；需要循环运动。一种常见的解决方案是螺旋丝的旋转，左旋或右旋均可。驱动每根细丝的鞭毛旋转马达无论顺时针还是逆时针旋转都会产生相同的扭矩。这种对称性通过与细丝耦合而被打破。最后，从置于单个点的接种物在营养培养基中生长的细菌群体，通常会以对称的圆环向外移动。在某些条件下，细胞会分泌一种化学引诱剂，圆环会分解成离散的聚集体，这些聚集体可以呈现出显著的几何秩序。
