Mechanoregulation of biofilm architecture promotes P. aeruginosa antibiotic tolerance

In the wild, bacteria are most frequently found in the form of multicellular structures called biofilms 1 . Biofilms grow at the surface of abiotic and living materials with wide-ranging mechanical properties. Despite their co-occurrence during infection, we still lack a clear understanding of how mechanics regulate biofilm architecture and the physiology of resident bacteria. The opportunistic pathogen Pseudomonas aeruginosa forms biofilms on indwelling medical device 2 and on soft tissues including burn wounds and the airway mucosa 3 . Here, we demonstrate that mechanical properties of hydrogel material substrates define P. aeruginosa biofilm architecture. We show that hydrogel mesh size regulates twitching motility, a surface exploration mechanism priming biofilms, ultimately controlling the arrangement of single cells in the multicellular community. The resulting architectural transitions increase P. aeruginosa ’s tolerance to colistin, a last resort antibiotic. Our results thereby establish material properties as a regulator of biofilm architecture and antibiotic efficacy.