Exploration of social spreading reveals behavior is prevalent among Pedobacter and P. fluorescens isolates, and shows variations in induction of phenotype

Within soil, bacteria are naturally found in multi-species communities, where interactions can lead to emergent community properties. It is critical that we study bacteria in a social context to investigate community-level functions. We previously showed that when co-cultured, Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48 engage in interspecies social spreading on a hard agar surface, a behavior which required close contact and was dependent on the nutritional environment. In this study, we investigate whether the ability to participate in social spreading is widespread among P. fluorescens and Pedobacter isolates, and whether the requirements for interaction vary. We find that this phenotype is not restricted to the interaction between P. fluorescens Pf0-1 and Pedobacter sp. V48, but is a more prevalent behavior found in one clade in the P. fluorescens group and two clades in the Pedobacter genus. We also discovered that the interaction with certain Pedobacter isolates occurred without close contact, indicating induction of spreading by a putative diffusible signal. As is the case for ISS by Pf0-1+V48, motility of all interacting pairs is influenced by the environment, with no spreading behaviors observed under high nutrient conditions. While Pf0-1+V48 require low nutrient but high NaCl conditions, in the broader range of interacting pairs this requirement for low nutrient and high salt was variable. The prevalence of motility phenotypes observed in this study and found within the literature indicates that community-induced locomotion in general, and social spreading in particular, is likely important within the environment. It is crucial that we continue to study microbial interactions and their emergent properties to gain a fuller understanding of the functions of microbial communities.