Bacterial swimming speed and rotation rate of bundled flagella

Swimming speed (1) and flagellar-bundle rotation rate (f) of Salmonella typ himurium, which has peritrichous flagella, were simultaneously measured by laser dark-field microscopy (LDM). Clear periodic changes in the LDM signal s from a rotating bundle indicated in-phase rotation of the flagella in the bundle. A roughly linear relation between 1 and f was observed, though the data points were widely distributed. The ratio of v to f(v-f ratio). Which indicates the propulsive distance during one flagellar rotation, was 0.27 mum (11% of the flagellar pitch) on average. The experimental,v-f ratio was tu ice as large as the calculated one on the assumption that a cell had a single flagellum. A flagellar bundle was considered to propel a cell more e fficiently than a single flagellum. (C) 2001 Federation of European Microbi ological Societies. Published by Elsevier Science B.V. All rights reserved.