Interspecies surfactants serve as public goods enabling surface motility in <i>Pseudomonas aeruginosa</i>

Bacterial motility is an important determinant of bacterial fitness and pathogenesis, allowing expansion and invasion to access nutrients and adapt to new environments. Here, we demonstrate that secreted surfactants from a variety of foreign species, including other bacterial species, infection hosts, fungi, and plants, facilitate surface spreading motility in the opportunistic pathogen <i>Pseudomonas aeruginosa</i> that is distinct from established motility phenotypes. This response to foreign surfactants also occurs in <i>Pseudomonas putida</i>, but not in more distantly related bacterial species. Our systematic characterization of surfactant-based surface spreading shows that these interspecies surfactants serve as public goods to enable <i>P. aeruginosa</i> to move and explore environmental conditions when it would be otherwise immotile.