SUMMARY: The flagellation and motility of were unaffected by proteolytic enzymes; but when washed stationary-phase bacteria were briefly exposed to acid (e.g. pH 2·6 for 30 sec. at 43°) the proportion of motile, and of flagellated, bacteria was decreased from more than 50% to less than 1%, with little or no decrease in viable count. When or grown on stiff agar were rubbed for several minutes on the agar, the proportion of motile and of flagellated bacteria was decreased from 90% (found in control bacteria, soaked off without rubbing) to 1%, without decrease in viable count. High-speed stirring in a blendor also deflagellated and destroyed the motility of in suspension, without killing the bacteria or retarding their growth. Blendor treatment sufficient to deflagellate had no effect on the movements of certain non-flagellated motile organisms ( and ), except when it caused gross morphological changes, attributed to cell damage. When log-phase broth cultures of deflagellated in the blendor were incubated, bacteria with flagella (at first all short) and motile bacteria soon reappeared. At first many bacteria rotated; this suggests that flagella shorter than 0·3 μ cause rotational, but not translational, motility. The rate of increase of mean summed flagellar length/bacterium was compatible with the hypothesis that flagella are not (spontaneously) shed in broth cultures of and that the rate of growth of flagella is unaffected by deflagellation. Up to one generation time after deflagellation the mean number of flagella/bacterium was, however, less than before deflagellation. It is inferred that in a log-phase culture about half the flagella present at any one moment are ‘fully-grown’, incapable of being regenerated when broken off. All the results obtained are compatible with the hypothesis that the motility of flagellated bacteria is due to active movement of their flagella.


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