Pseudomonas aeruginosa senses exopolysaccharide trails using type IV pili and adhesins during biofilm formation

Abstract

During early stages of biofilm formation, Pseudomonas aeruginosa (Pa) PAO1 can sense exopolysaccharide (EPS) trails of Psl deposited on a surface by previous Pa cells to detect trajectories of other cells and to orchestrate motility. This sensory signal is transduced into cyclic diGMP second messengers, but no known Psl receptors and adhesins participate in signal transduction. Here, using bacteria-secreted Psl trails, glycopolymer-patterned surfaces, longitudinal cell tracking, second messenger dual reporters and genetic mutations targeting EPS binding and surface twitching, we find that Pa is capable of sensing EPS directly through mutually constitutive interactions between type IV pili (T4P)-powered twitching and specific adhesin–EPS bonds. This unanticipated mechanochemical surveillance of the Pa environment, where T4P pull against cell-body localized adhesins interacting with EPS trails, such as mannose-binding CdrA, generates a hybrid, transitional planktonic-to-biofilm population with elevated cyclic diGMP and elevated cyclic AMP, as well as increased motility capable of following EPS trails. These results show a generalizable mechanism of surface chemosensing through mechanosensitive appendages. Opposing forces generated by exopolysaccharide trail binding versus type IV pilus retraction generate a high cyclic diGMP–high cyclic AMP state in Pseudomonas aeruginosa that promotes social motility.