la302056j_si_002.avi (2.4 MB)
Coiled to Diffuse: Brownian Motion of a Helical Bacterium
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posted on 2012-09-11, 00:00 authored by Alexander
V. Butenko, Emma Mogilko, Lee Amitai, Boaz Pokroy, Eli SloutskinWe employ real-time three-dimensional confocal microscopy
to follow
the Brownian motion of a fixed helically shaped Leptospira
interrogans (LI) bacterium. We extract from our measurements
the translational and the rotational diffusion coefficients of this
bacterium. A simple theoretical model is suggested, perfectly reproducing
the experimental diffusion coefficients, with no tunable parameters.
An older theoretical model, where edge effects are neglected, dramatically
underestimates the observed rates of translation. Interestingly, the
coiling of LI increases its rotational diffusion coefficient by a
factor of 5, compared to a (hypothetical) rectified bacterium of the
same contour length. Moreover, the translational diffusion coefficients
would have decreased by a factor of ∼1.5, if LI were rectified.
This suggests that the spiral shape of the spirochaete bacteria, in
addition to being employed for their active twisting motion, may also
increase the ability of these bacteria to explore the surrounding
fluid by passive Brownian diffusion.