Abstract
Bacteria often live in complex communities in which they interact with other organisms. Consideration of the social environment of bacteria can reveal emergent traits and behaviors that would be overlooked by studying bacteria in isolation. Here we characterize a social trait which emerges upon interaction between the distantly-related soil bacteria Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48. On hard agar, which is not permissive for motility the mono-culture of either species, co-culture reveals an emergent phenotype we term 'social motility,' where the bacteria spread across the hard surface. We show that initiation of social motility requires close association between the two species of bacteria. Both species remain associated throughout the spreading colony, with reproducible and non-homogenous patterns of distribution. The nutritional environment influences social motility; no social behavior is observed under high nutrient conditions, but low nutrient conditions are insufficient to promote social motility without high salt concentrations. This simple two-species consortium is a tractable model system that will facilitate mechanistic investigations of interspecies interactions and provide insight into emergent properties of interacting species. These studies will contribute to the broader knowledge of how bacterial interactions influence the functions of communities they inhabit.
