Bacillus subtilis spreads by surfing on waves of surfactant

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Reference

Bacillus subtilis spreads by surfing on waves of surfactant

Angelini T.E., Roper M., Kolter R., Weitz D.A., Brenner M.P.

PNAS 106: 18109-18113 (2009) PMID: 19826092 (Pubget)

Motivation

In times of stress Bacillus subtilis form a dense mat of exopolysacharides that allows the bacteria to bind to solid or liquid surfaces. The molecular signaling underlying the initiation and growth of biofilms have been extensively studied. One under-studied question, though, is the nature of the mechanism by which biofilms spread. The spreading is initiated when nutrients in the environment run low, and has probably evolved to help B. subtilis find new food sources.

Experimental Observations

Hypothesis

Conceptual Explanation

A 'B. subtilis' biofilm is thicker in the center that at the edges. If we assumed that:

  • Surfactin secreted by cells moves quickly to the air-biofilm interface.
  • Surfactin reduces the film surface tension.
  • All cells secrete surfactin at the same rate.
  • The bacteria are homogeneously distributed throughout the film.

Scaling Analysis

Mathematical Model