Figure 5.

A) Microscopic analysis of the bacterial tumbles. The major axis of a fluorescent bacterium in projection in the observation plane of a microscope forms an angle ψ with a direction of reference (image width 5 µm).ψ was measured experimentally by fitting the projected shape by an ellipse. These experiments were performed on bacteria that always tumble (“tumbler” strain CR33) (see Movie S1). B) Temporal evolution of the orientation. Angle ψ (in the observation plane) of the major axis of the bacteria (for 20 different tumblers) as a function of time. C) Temporal autocorrelation function versus time. The projected directional correlation functions were obtained for “tumbler mutants” in LB medium (red circles) and in M9 medium (black circles). These experimental curves were fitted (solid lines) by a single exponential and give respectively for the only adjustable parameter D_r^LB = 2.4 rad²/s and D_r^M9 = 1.6 rad²/s.