Yasunari Takano

An Engineering Perspective on Swimming Bacteria:High-Speed Flagellar Motor, Intelligent Flagellar Filaments, and Skillful Swimming in Viscous Environments

Many bacteria swim by rotating their helical flagellar filaments which are driven by flagellar motors embedded in the cell membranes. In mechanical engineering, bacterial swimming is an interesting subtopic of robotics and nano-mechanics since countless nano-machines made of bio-molecules are packed into 1 µm cells. In this paper, we present three exceptionally interesting facts about swimming bacteria, which have been known for the past decade. First, a flagellar motor rotates extremely fast (the maximum recorded is 1,700 rps). This information produces many new questions regarding, for example, the torque generation mechanism and the wear. The second fact concerns the flagellar filament as an intelligent material. It is sufficiently rigid for a use as a propeller and yet can change its helical form to relax the stress when an excessive force acts on it. The mechanism is now being explored at an atomic level. The last fact is that bacterial cells sometimes swim well in viscous environments. This phenomenon contradicts common knowledge but could be explained by a new hypothesis in which the effect of the polymer network on the bacterial motion was expressed mathematically. We were impressed by the acumen of bacteria. (Review)