A trait-based approach to bacterial biofilms in soil

A trait-based approach focuses on attributes of taxa that influence the structure and function of communities. Biofilm production is a trait that is common among microorganisms in a wide range of environmental, engineered, and host-associated ecosystems. In this study, we present experimental evidence linking biofilm production to moisture availability, which is one of the greatest challenges for microorganisms living in the soil environment. Using Pseudomonas aeruginosa as a model system, first, we demonstrate that biofilm production is a response trait that affects bacterial performance under dry conditions. In addition to increasing survivorship, biofilm production affected the desiccation phenotype by shifting the niche space and reducing the minimum water potential needed to sustain a net-positive growth rate (Ψ*). Although the allocation of resources to biofilms is thought to be costly, we found we no evidence to support a hypothesized trade-off between bacterial fitness and biofilm production along a moisture gradient. Second, we demonstrated that biofilm production is an effect trait. Specifically, biofilm production increased soil water retention in soils that were exposed to a series of drying and rewetting cycles. Although this form of niche construction via the release of public goods should affect species interactions, we found no evidence that biofilm production modified the performance of another soil bacterium. Together, our results support the view that biofilm production is an important functional trait that may contribute to the distribution, abundance, and functioning of microorganisms in soil environments.