Swimming Using a Unidirectionally Rotating, Single Stopping Flagellum in the Alpha Proteobacterium Rhodobacter sphaeroides

Abstract

Rhodobacter sphaeroides has 2 flagellar operons, one, Fla2, encoding a polar tuft that is not expressed under laboratory conditions and a second, Fla1, encoding a single randomly positioned flagellum. This single flagellum, unlike the flagella of other species studied, only rotates in a counterclockwise direction. Long periods of smooth swimming are punctuated by short stops, caused by the binding of one of 3 competing CheY homologs to the motor. During a stop, the motor is locked, not freely rotating, and the flagellar filament changes conformation to a short wavelength, large amplitude structure, reforming into a driving helix when the motor restarts. The cell has been reoriented during the brief stop and the next period of smooth swimming is a new direction.

Rotation of the Fla2 flagella of Cereibacter sphaeroides requires the periplasmic proteins MotK and MotE that interact with the flagellar stator protein MotB2

“…Fla1 and Fla2 rotate unidirectionally, and reorientation is achieved by controlling the frequency of short stop events [67,73]. During smooth swimming periods, cells reach average velocities of 27 to 50 μm/s when swimming with the Fla1 flagellum [74][75][76][77], and approximately 61 μm/s with Fla2. Complex chemotactic systems control each of these flagellar motors and noteworthily, the expression of the chemotactic genes is coordinated by the transcriptional factors that control the expression of their cognate flagellar system [78].…”