Fig. 3. PilU does not affect TFP dynamics in free solution.

(a) iSCAT images of pilT^- fliC^- and pilU^- fliC^- mutants. pilT^- fliC^- cells never undergo retraction on the timescale of our movies. The pilU^- fliC^- mutant picture shows a retraction of one TFP. The black arrow indicates a tensed pilus; the white arrows indicate floppy pili. Scale bar: 2 µm. (b) Number of TFP in motor mutants and their corresponding complementation strains. These have similar numbers of surface pili except pilT^- fliC^- (number of cells from the same culture n = 11), which had more (fliC^- n = 15, pilT^- fliC^- complemented n = 15, pilU^- fliC^- n = 18, pilU^- fliC^- complemented n = 17). Large circles are means of bootstrap medians and error bars bootstrap 95% confidence intervals. Small circles are individual measurements. (c) The average lengths of TFP that attached on the glass surface in fliC^- (combined number of pili from cells imaged in at least three biological replicates n = 54), pilU^- fliC^- (n = 47) and pilT^- fliC^- (n = 45). (d) Retraction frequencies for pilU^- mutant (combined number of pili from cells imaged in at least three biological replicates n = 23,) compared to fliC^- (n = 23). The pilU^- mutant show a slight decrease in retraction frequencies compared to fliC^-. (e) Average displacement per retraction for fliC^- (number of tracks n = 13) and pilU^- fliC^- (n = 15). Motility does not strongly differ between these mutans. (c,d,e) Small circles correspond to individual measurements, large circles are medians of bootstrap medians and error bars are bootstrap 95% confidence interval. A difference between two groups is defined as statistically significant when their 95% confidence intervals don’t overlap.