Microbial invasion ecology: community-level effects of biological invasions in bacterial microcosm model systems

Laboratory microcosm systems provide researchers with an invaluable tool to rapidly model real-world ecology in a highly-controlled environment. These models have already proved capable of predicting real-world outcomes in relation to a variety of ecological processes, but further microcosm investigations, and comparisons with real-world studies, are required before these systems can be relied upon as rapid diagnostic tools which can inform real-world management decisions. Here, the use of microcosm systems to model ecological processes involved in biological invasion events is discussed, and three experiments relating to these processes are described. 1) Preadaptation of Pseudomonas fluorescens to the biotic and abiotic environmental conditions in a soil microcosm was found to drive diversity within the P. fluorescens population, including genetic, morphological, and metabolic diversity. When inoculated into soil microcosms alongside a resident soil community, this diversity within this focal population drives greater changes in the community structure of the resident soil community compared with ancestral P. fluorescens SBW25. Interestingly, diversity of the focal population was found to be the single most important driver of changes in resident community structure, over the effects of fitness and of direct adaptations to the environment itself. 2) Preadaptation to disturbance-related mortality events may provide species with a competitive advantage during and after such events. Here, P. fluorescens populations preadapted to a range of disturbance regimes were subjected to competitive fitness assays in KB broth under both the regimes they were preadapted to, and the full range of regimes investigated. At 99% mortality of resident populations, disturbance frequency was found to have a non-significant correlation with the morphological diversity of populations recovered at the end of the experimental period. As previous work has found significant effects of disturbance upon P. fluorescens morphological diversity using a similar system, at 99.9% mortality, this study indicates that further work with this system may yield results of interest either using higher intensities or higher frequencies of disturbance than were investigated here. 3) Using whole natural microbial communities to study ecological processes within a microcosm system provides rapid results comparable to the complexities of real-world ecological systems, however, current understanding of the complex relationships of diverse microbial communities with the biotic and abiotic components of their environment are not currently fully understood. In order to truly understand the changes in resident community structure when conducting microcosm studies, a good understanding of the niche-space used by each member of the community is desirable. Here, a series of simple experiments yielded a small community of 5 microbial species that could be distinguished by eye beyond the end of a 6-week co-existence study. This lays the foundations for building an artificial community that can be easily characterised and manipulated when investigating ecological processes in microcosm systems, and provide data on changes in community structure without the need for complex or expensive equipment and techniques.Natural Environment Research Council (NERC