ATPase assay of OtrC-overexpressing and OtrC-nonexpressing cells. OtrC from S. rimosus was introduced into the E.coli BL21(DE3) strain using a pETC02 plasmid, and the E.coli BL21(DE3) carrying the empty pET28a was used as the control. The cells were induced by 1 mM IPTG at 30°C for 10 h, and then collected by centrifugation. The cell wall was digested by lysozymes and the membrane vesicles were harvested by centrifugation. The ATPase activity of E.coli/pETC02 (dark gray) was determined compared with to the E. coli/pET28a control (light gray). Vertical error bars corresponded to the standard error of the mean of three replicated samples.