Microbes are responsible for most of the carbon and nutrient cycling in freshwater lakes, and influence both local water quality and global carbon budgets. However, it is not currently possible to predict which types of microbes will be found in a particular lake at a particular time, or to predict how a microbial community would respond to environmental change. Microbial biologists need to learn more about how microbes in lakes assemble into communities, the role of drivers such as competition, predation, resource availability, disturbance, and natural selection in shaping these assemblages. This project addresses the following overarching question: What forces organize microbial communities in humic lakes? Microbes and their communities respond to many forces acting at different spatial and temporal scales, and the effect of these forces can be observed at the level of both communities and populations. An interdisciplinary team of microbiologists, ecologists, engineers, and limnologists will use a suite of molecular tools and genomics to investigate (1) Interactions between bacteria and phytoplankton in the surface layers of lakes; (2) Changes in microbial communities resulting from water column disturbances such as thermal stratification and seasonal mixing and (3) The role of evolutionary processes in shaping individual microbial populations within and among lakes. The results of this work will allow us to better explain and ultimately predict the composition and dynamics of microbial communities and populations in freshwater lakes.
This project will not only advance our understanding of the microbial ecology of humic lakes, but of microbial ecology and biodiversity in a broader context. The research approach is structured within an ecological framework and reflect urgent questions in the field of microbial biology. To enhance the broader impacts of the work, the investigators will engage in outreach activities coordinated with the following organizations; the NTL-LTER SchoolYard Science program which promotes inquiry-based learning through workshops for high-school teachers; the Center for Biology Education which is developing a virtual professional development resource for middle and high school science and mathematics teachers; the UW-Madison PEOPLE program which organizes summer courses for underrepresented high-school students; the NSF-funded Center for the Integration of Teaching, Research, and Learning which promotes professional development of graduate students, post-docs, and faculty. The research team will continue to leverage these existing programs to show the general public how freshwater microbes are key components of lake ecosystems, impacting water quality and nutrient cycling in profound ways.
The overarching goal of this project was to identify and describe the forces organizing microbial communities along expanding spatial, temporal, and taxonomic scales of resolution in humic lakes. Aim 1: Determine which biological interactions are most important in structuring community dynamics within a single lake. Outcomes: We linked the dynamics of key bacterial groups to known drivers of community composition: phytoplankton community composition, light, and temperature. We now know which lineages respond to variations in these drivers, providing us with new insight into ecological interactions and key traits for important freshwater bacterial groups. Aim 2: Evaluate how disturbance influences community structure and dynamics at regional scales. Outcomes: Our results have implications for understanding microbiological responses to environmental perturbations at both fine and coarse temporal scales. In this study, the microbial communities changed after the disturbance, exhibiting sensitivity to a pulse perturbation that occurred over a relatively short time scale (one week). Further, the clear connection between biogeochemical conditions and BCC suggests that there are direct linkages between changes in environmental forcing, biogeochemical conditions, and microbial communities. Work by our group and others has shown repeatable seasonal patterns in microbial communities inhabiting rivers, oceans, seas, and lakes, providing cumulative evidence of a consistent microbial community "baseline" that spans many aquatic systems. In ecology, increases in ecosystem variance have been suggested as indicators of ecological regime shifts. Therefore, gradual changes in aquatic microbial communities that exceed normal variability may correspond to press disturbances, such as those expected with gradual global change (e.g. increases in mean temperature). Aim 3: Identify the effects of natural selection on population and community structure. Outcomes: Our findings highlight the importance and feasibility of examining ecological change in microbial communities across taxonomic scales while also providing valuable insight into the ecological characteristics of ecologically coherent groups. We found that change in the population structure of a single genotype can provide additional insight into the mechanisms of community-level responses. Broader impacts: This project has provided training for 6 PhD students, 2 MS students, and 14 undergraduate students. Our work has been broadly disseminated through publication in conventional peer-reviewed scientific literature. Graduate students and the PI presented work at scientific conferences throughout the project period. We were and remain particularly engaged with the Global Lakes Ecological Observatory Network (GLEON). We have engaged in outreach activities related to water quality with the Campus Middle School for Girls, the Children's Science Museum of Champaign, IL, and the Illinois State Envirothon Competion. In addition, PI Kent has taught 2 graduate and 2 undergraduate courses about microbial community ecology methods.
