Bitzer, A. S. | Search bioRxiv

bioRxiv2019

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.

microbiology↗

bioRxiv2018

Social Motility: Interaction between two sessile soil bacteria leads to emergence of surface motility

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 of the mono-culture of either species, co-culture reveals an emergent phenotype we term interspecies social spreading, where the mixed colony spreads across the hard surface. We show that initiation of social spreading 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 spreading; no social behavior is observed under high nutrient conditions, but low nutrient conditions are insufficient to promote social spreading 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.\n\nImportanceThe wealth of studies on microbial communities has revealed the complexity and dynamics of the composition of communities in many ecological settings. Fewer studies probe the functional interactions of the community members. Function of the community as a whole may not be fully revealed by characterizing the individuals. In our two-species model community, we find an emergent trait resulting from the interaction of the soil bacteria Pseudomonas fluorescens Pf0-1 and Pedobacter sp. V48. Observation of emergent traits suggests there may be many functions of a community that are not predicted based on a priori knowledge of the community members. These types of studies will provide a more holistic understanding of microbial communities, allowing us to connect information about community composition with behaviors determined by interspecific interactions. These studies increase our ability to understand communities, such as the soil microbiome, plant-root microbiome, and human gut microbiome, with the final goal of being able to manipulate and rationally improve these communities.

microbiology↗