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Coiled to Diffuse: Brownian Motion of a Helical Bacterium

By Alexander V. Butenko (2046349), Emma Mogilko (2046346), Lee Amitai (2046352), Boaz Pokroy (1407205) and Eli Sloutskin (2046343)


We 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

Topics: Biophysics, Ecology, Computational Biology, Biological Sciences not elsewhere classified, diffusion coefficients, bacterium, LI, factor, bacteria, Brownian, model, translational diffusion coefficients
Year: 2012
DOI identifier: 10.1021/la302056j.s002
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Provided by: FigShare
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