Swimming assay of BTPS (a stator-less E. coli mutant expressing Bt-MotPS) in the presence of flagellar motor inhibitor. The Bt-PS and E. coli W3110 strains were grown for 7 h at 30 °C in LB medium containing 0.1% arabinose with shaking. B. pseudofirmus OF4 was grown for 7 h at 30 °C in MYE medium (pH 10.5) with shaking. Cells were suspended in 1 mL of swimming buffer (pH 7.0) plus several carbonyl cyanide m-chlorophenyl hydrazine (CCCP) concentrations (A1 and A2), plus several 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) concentrations (B1 and B2), plus several valinomycin concentrations (C1 and C2) and were incubated at 30 °C for 10 min. Swimming buffer contained 30 mM TES, 5 mM glucose, 0.1% arabinose, 100 mM NaCl (A1, B1 and C1) or 100 mM KCl (A2, B2 and C2), adjusted to pH 7.0 with N-methyl-D-glucamine. The results represent the average swimming speed of 30 independent cells from three independent experiments. The error bars indicate the standard deviations.