Abstract
The motility of spirochete improves in viscous environments. Such phenomena cannot be observed in the macroscopic world. One of the authors has proposed a hypothesis that predicts increase of the motion efficiency with the viscosity because the polymer molecules form a quasi-rigid network. To examine the hypothesis experimentally, we simultaneously measured the swimming speeds and rotation rates of a spirochete Brachyspira pilosicoli in polymer solutions by two-directional-illuminated dark-field microscopy (2DDM), which is an originally developed method to measure rotation rate of a helical body. This experimental result illustrated increase of the motion efficiency with viscosity. Therefore, we concluded that the improvement of spirochete motility in viscous environments at least partly relates with increase of the motion efficiency caused by a quasi-rigid network of polymer molecules.
