Chemical modification of Streptococcus flagellar motors

Video techniques were used to record changes in motility of cells of Streptococcus sp. strain V4051 exposed to a variety of protein modification reagents. Starved cells were tethered to glass by a single flagellum, energized metabolically with glucose, or treated with valinomycin and energized artificially via shifts to media containing low concentrations of potassium ion. Experiments were devised that distinguished reagents that lowered the proton motive force from those that blocked the generation of torque (damaged the flagellar motors). Imidazole reagents blocked the generation of torque. Amino, sulfhydryl, dithiol, and disulfide reagents did not. Some of the imidazole, amino, and sulfhydryl reagents had long-term effects on the direction of flagellar rotation.