Sessile bacterium unlocks ability of surface motility through mutualistic interspecies interaction

In addition to their common planktonic lifestyle, bacteria frequently live in surface-associated habitats. Surface motility is essential for exploring these habitats for food sources. However, many bacteria are found on surfaces, even though they lack features required for migrating along surfaces. How these canonical non-motile bacteria adapt to the environmental fluctuations on surfaces remains unknown. Recently, several cases of interspecies interaction were reported that induce surface motility of non-motile bacteria either by using 9hitchhiking9 strategies or through 9social spreading9 mechanisms. Here, we report a previously unknown mechanism for interaction-dependent surface motility of the canonical non-motile bacterium, Dietzia sp. DQ12-45-1b, which is induced by interaction with a dimorphic prosthecate bacterium, Glycocaulis alkaliphilus 6B-8T. Dietzia cells exhibits 9sliding9-like motility in an area where the strain Glycocaulis cells was pre-colonized with a sufficient density. Furthermore, we show that biosurfactants play a critical role in inducing the surface motility of Dietzia cells. Our analysis also demonstrates that Dietzia degrade n-alkanes and provide Glycocaulis with the resulting metabolites for survival, which in turn enabled directional migration of Dietzia towards nutrients in the environment. Such interaction-dependent migration was also found between Dietzia and Glycocaulis strains isolated from other habitats, suggesting that this mutualistic relationship ubiquitously occurs in natural environments. In conclusion, we propose a novel model for such a 9win-win9 strategy, whereby non-motile bacteria pay metabolites to dimorphic prosthecate bacteria in return for migrating to reach environments otherwise inaccessible. We propose that this mechanism represents a common strategy for canonically non-motile bacteria living on a surface.