Harry Swinney

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  Collective dynamics, deadly competition, and a shape-changing transition in bacterial colonies
  Harry Swinney

  Bacillus subtilis bacteria in a growing colony are observed to exhibit giant fluctuations in the number N in a given volume: the rms fluctuation is proportional to N^(3/4) rather than N^(1/2) as in systems in thermodynamic equilibrium. Measurements of the speed and orientational correlations of bacteria within a growing colony yield an unexpected scale invariance. Studies of another rod-shaped motile bacterium common in soil, Paenibacillus dendritiformis, reveal that neighboring colonies secrete a previously unknown toxic protein, Slf, which is not secreted by an isolated colony. Models help in understanding the growth inhibition and why the competition between neighboring colonies is deadly. Some bacteria within a colony survive Slf by switching to an immotile Slf-resistant coccus (spherical) form. If cocci encounter sustained favorable conditions, they switch back to the rod-shaped form. Genes that encode components of this shape-changing transition are widespread among bacterial species, suggesting that this survival mechanism is not unique to P. dentritiformis.