Biocomplexity: The Roles of Resources, Competition, and Predation in Microbial Degradation of Organic Matter

点击翻译按钮获取中文摘要

ABSTRACTOCE-0120610Bacteria play crucial roles in cycling of elements and thus the functioning of the biosphere. We know a great deal about the metabolic diversity of bacteria, and the pathways of the reactions they perform. Outside of simple laboratory systems, however, we cannot predict with any certainty the rates at which bacteria grow, metabolize, and mineralize organic matter. This project is about understanding, at a mechanistic and thus quantitative level, what affects the activity of bacteria in nature. While initially the problem seems straightforward, the investigators believe that its solution has been elusive because there are complex processes involved. This complexity exists over several levels of biological organization (individual, population, community), and in the microscale spatial heterogeneity of the environments in which bacteria function. The ultimate goal of this study is to develop, and test, a model that will predict the rates of organic matter cycling in natural systems. Such a model must include the physical and chemical factors controlling the availability of resources (reactants) to bacteria, interactions (potentially competitive) among different bacterial populations, and interactions among bacteria and their predators. The shorter-term goal, and the explicit goal of this project, is to focus on one type of environment - estuarine sediments - and one category of organic matter - polycyclic aromatic hydrocarbons (PAHs) in a background of natural organic matter. The approach centers on a tight coupling between modeling and empiricism, since it is our belief that models and experiments lead to new, useful knowledge only when there is a steady interaction. The model we will develop considers both bottom-up (e.g., resource availability) and to-down (e.g., predation) controls on bacterial activity. Estuarine sediment will be used as the environmental matrix for modeling and experimental testing inasmuch as these sediments are inherently complex and heterogeneous due to their widely varied chemical and physical properties, the mixtures of organic and inorganic constituents of which they are composed, and the simultaneous occurrence of chemical, physical, and biological processes. Bicyclic and polycyclic aromatic hydrocarbons (PAHs) will be chosen as a type of reactant that is used by only certain types of bacteria in the system. Thus, the time rate of change in PAHs will be used as a barometer of the activity of some members of the community. This will provide a sensitive and specific comparison of model predictions and experimental data. Models will be structured to account for variability in properties of the biological and abiotic components. The framework of the models will include spatial heterogeneity in sediment properties, population dynamics including competition and predation, nutrient and PAH mass transfer, and molecular dynamic simulations. Complexity will be added incrementally, as indicated by closely coupling model predictions with experimental results. The expertise of the group assembled to conduct the proposed research encompasses ecology, engineering, environmental geochemistry, and microbiology. Educational and training opportunities, on a variety of levels, will be built into this research. Specifically, the project will include mechanisms to enhance coursework in both undergraduate and graduate programs in environmental technology and engineering education; to broaden student research training that will explore dynamic interactions within and among environmental systems and will be directed by a multidisciplinary team of faculty investigators; and to provide enrichment opportunities for in-service teachers of science courses in grades 5-8 through a partners-in-learning program.