Mutation of LC1 alters flagellar propulsive force generated under varying viscous load. (top) The beat frequency and propulsive force generated under varying viscous load is shown for wild type (cc124) and for strains lacking the entire outer arm (oda6), the motor domains of the β and γ HCs (oda4-s7 and oda2-t), and for a strain lacking both the β HC motor unit and the entire α HC (oda4-s7 oda11). (bottom) Similar plots for three strains expressing M182G, R189E, and R196A mutant forms of LC1 are shown. All three mutants generated reduced propulsive force under low viscous load, but this was enhanced as the load increased. This response approximates the behavior of the oda2-t mutant. Each point represents the mean propulsive force calculated from the swimming velocity of 10 cells. Bars indicating the SDs have been omitted for clarity; for all but two points on the cc124 and M182G plots, SDs ranged from 0.45–2.94 pN. Beat frequency data were obtained using the population-based fast Fourier transform method, and each determination was performed in triplicate.