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Phénomènes d'étalement et de mouillage à la surface d'un gel et implications pour la migration en masse chez B. subtilis

Abstract : Gels wetting draws fondamental interest from Physics industry and also Biology: when bacteria Bacilus.Subtilis mass migrates on gel culture medium, it produces surfactin, a powerfull surfactant. We develop an optical setup for the visualisation of the free surface of a spreading drop on agar gel. A drop containing surfactin spreads spontaneously. When it starts to retract, a surfactin front appears all around the edges and propagates according to a radial expansion in power law with times . The measured spreading coefficients are unexpectedly and we propose phenomenological explanations for this slow dynamics. The dynamics shows dependences on agar concentration and on the medium chemical composition. We discuss similarities between our observations and swarming of B.Subtilis for which front dynamics and dendritic expansion seems strongly correlated. Surprisingly, a partial wetting situation is observed in the case of pure water drops on the agar gel surface which contains up to 99,5% of the same liquid. We measure an important wetting hysteresis only partially linked to the soft character of the subtrates. Existing models failed to describe our measuress and we propose a more general model including gel surface tension which shows better agreement with our observations.
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https://pastel.archives-ouvertes.fr/tel-00474047
Contributor : Mehdi Banaha <>
Submitted on : Sunday, April 18, 2010 - 11:24:11 PM
Last modification on : Saturday, September 26, 2020 - 11:44:06 PM
Long-term archiving on: : Monday, October 22, 2012 - 3:10:45 PM

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  • HAL Id : tel-00474047, version 1

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Mehdi Banaha. Phénomènes d'étalement et de mouillage à la surface d'un gel et implications pour la migration en masse chez B. subtilis. Biophysique [physics.bio-ph]. ESPCI ParisTECH, 2009. Français. ⟨tel-00474047⟩

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