Flagellar bundle

Figure 34.34. Chaugiug Direction. Tumbling is caused by an abrupt reversal of the flagellar motor, which disperses the flagellar bundle. A second reversal of the motor restores smooth swimming, almost always in a different direction. [After a drawing kindly provided by Dr. Daniel Koshland, Jr.]...

In the absence of stimuli, halobacterial cells spontaneously switch the rotational sense of their flagellar bundle. The time course of the probability for spontaneous motor switching was calculated from frequency distributions and was shown to be independent of the rotational sense [22]. Switching occurs with a constant probability per unit of time except in the early phase immediately after a switching event. Kinetically, spontaneous switching... 

The cells exhibit smooth swimming, reversals, flexing, and pausing. When the flagellar bundles at both cell poles rotate in opposite directions (one pulls and one pushes), the cell swims in a rather straight line. When the two bundles switch synchronously, the cell reverses. When the two bundles rotate in the same direction, the cell flexes. 

Kupper, J., Marwan, W, Typke, D., Griinbeig, H., Uwer, U., Gluch, M. and Oesterhelt, D. (1994). The flagellar bundle of Halobacterium salinarium is inserted into a distinct polar cap structure./. Bacteriol. 176, 5184—5187. 

Lowe, G., Meister, M. and Berg, H.C. (1987). Rapid rotadon of flagellar bundles in swimming bacteria. Nature 325, 637-640. 

The filaments of the flagellar bundle of E. coli all rotate in the same direction. Tumbling requires simultaneous reversal of all the flagellar rotors. Similarly the bundles of Spirillum although at opposite poles of the cell exhibit synchronous changes in rotational direction. These properties suggest the existence of a central co-ordinating system, possibly an electrochemical mechanism, similar to that of the ciliate protozoa. 

S. melUoti Increased speed of flagellar rotation. Consequently, rnns are prolonged. Decreased speed of flagellar rotation. Consequently, the bundle of rotating flagella separates to individual filaments rotating at different speeds, and the cell turns. [675]... 

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