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Convergent evolution of hyperswarming in experimental bacterial populations Xavier, Joao


The opportunistic pathogen Pseudomonas aeruginosa forms biofilms in cystic fibrosis lungs that are notoriously difficult to treat with antibiotics. Alternative approaches are desperately needed to fight these biofilm infections. One possibility lies in the inverse genetic regulation of motility and biofilm formation of P. aeruginosa. We investigated whether pushing the bacterium to a motile state makes it form less biofilm. In evolutionary experiments we applied a selective pressure for swarming, a collective form of motility where colonies of P. aeruginosa form striking branched patterns on soft surfaces. The experiments consistently produced P. aeruginosa mutants that went from being mono-flagellated, their natural state, to become multi-flagellated, which made them swim faster and out-compete the ancestral strain. The advantage in swarming came with a trade-off: multi-flagellated mutants do not compete well in biofilm communities, which would be essential for their survival in environmental and clinical settings. The observation that selection for superior motility consistently leads to the evolution of weak biofilm formers could open new therapeutic avenues against persistent biofilm infections.

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