Pressure-Speed Relationship of the Sodium-Driven Flagellar Motor of Vibrio Alginolyticus

Abstract

The bacterial flagellar motor is a molecular machine that converts an ion flux to the rotation of a helical flagellar filament. Motor rotation rate and directions can be changed by environmental factors such as temperature, pH, and solvation. Hydrostatic pressure is also an inhibitor of the rotation of flagellar motors [1, 2]. Our previous results indicated that the application of pressure inhibits the rate of ion tranlocation in the mechanochemical energy translation, but the detailed mechanism is still unknown. Here, we characterized the pressure dependence of the rotational speed of sodium-driven flagellar motor in swimming Vibrio alginolyticus cells. The motor in strain NMB136 exclusively rotates in counter-clockwise direction and propells the cell body forward. We monitored the pressure-induced effects on the behavior of the cells that swim freely in solution. The swimming speed exponentially decreased with the increment of pressure. The sodium concentration dependence of the swimming speed at each pressure was well described by a Michaelis-Menten kinetics. The applied pressures decreased the maximum velocity, but increased the Michalis constant. Our results showed that the motor has at least two pressure-sensitive reactions, one of which is the binding process of external sodium ions to the motor. Another is the post-sodium-binding process, suggesting sodium transit and/or its release to inside the cell.[1] Nishiyama M. and Y. Sowa. 2012. Microscopic Analysis of Bacterial Motility at High Pressure. Biophys. J.102:1872-1880.[2] Nishiyama M. et al. 2013. High Hydrostatic Pressure Induces Counterclockwise to Clockwise Reversals of the Escherichia coli Flagellar Motor. J. Bactetiol.195: 1809-1814.