Cinemicrographic analysis of the movement of flagellated bacteria. I. The ratio of the propulsive velocity to the frequency of bodily rotation.

On the basis of the hydrodynamic model that the propulsion of flagellated bacteria in a fluid is a consequence of the propagation of helical waves along the length of flagella or flagellar bundles, it is predicted that propulsion must be accompanied by a rotation of bacterial body about the direction of translation (Chwang and Wu, 1971), and that propulsive velocity u is directly proportional to the frequency of bodily rotation fB, the proportional constant being a complicated function of various parameters describing the sizes and shapes of body and flagella. In this study we have measured not only u but also fB by cinemicrography or sometimes by dual cinemicrography, using a mono- trichously flagellated Pseudomonas strain and a multitrichously flagellated Salmonella strain, and calculated the ratio u/fB. Though the values of u/fB thus determined for a number of bacteria of each strain scattered in a wide range, average values of u/fB were likely to be independent of u, in support of the theoretical prediction. Moreover, in Pseudomonas as well as in Salmonella, it was found that the experimental values of u/fB were in semiquantitative agreement with theoretical values expected from the hydrodynamic model for appropriate values of the geometrical parameters. Taking into account these results, it was concluded that the validity of this model has been supported experimentally.