This project will explore mechanisms of microbially-catalyzed iron (Fe) redox cycling in anaerobic sediments. Iron is the fourth most abundant element in the Earth's crust, and its redox cycling exerts a strong influence on the behavior of various organic and inorganic compounds in both aquatic and terrestrial ecosystems. The structure and function of microbial communities associated with Fe redox cycling in near-surface environments is therefore an important topic in environmental microbiology and biogeochemistry. This project addresses several unique aspects of microbial community structure and physiology related to Fe redox cycling and biomineralization in modern subsoils and shallow groundwater environments. Such environments are primary receptors of both natural and anthropogenic materials (e.g. run-off from urban and agricultural systems), and microorganisms play a key role in subsurface biogeochemical processes. The proposed research will explore novel strategies that microbial populations and communities may utilize to derive energy from Fe redox cycling, and will examine the mineralogical signatures of such activities. Experimental reactive transport systems will be used to mimic natural subsurface environments in which temporal variations in the input of electron donors and acceptors are expected to strongly influence microbial community development and patterns of Fe biomineralization. The experimental systems will support microbial communities from either a freshwater wetland surface sediment or shallow Atlantic Coastal plain aquifer sediment. We hypothesize that the energy available from Fe and nitrogen redox interactions will lead to the development of microbial populations and/or communities specifically adapted to take advantage of the energy available during redox oscillations. In addition, we anticipate that the Fe mineralogy of sediments subject to redox fluctuations will evolve toward a suite of metastable minerals of relative low crystallinity and high reactivity relative to those in sediments under stable redox conditions. The reactor systems to be developed in this study represent novel research techniques for examining linkages between microbial physiology, community structure, biogeochemical reaction dynamics, and Fe biomineralization. The geomicrobiological and biogeochemical information gained from these model systems will be incorporated into a microbial energetics-based numerical simulation framework that will allow the results of our experimental studies to be transferred to a variety of surface and subsurface sedimentary environments. The project will train two Ph.D. students in multidisciplinary biogeochemical research methodologies as well as techniques for numerical simulation of biogeochemical processes and microbial population dynamics in sediments. An undergraduate intern will participate in microbial culturing and isolation at IU. The UW Ph.D. student will participate in the training of a summer Research Experience for Teachers (RET) fellow. The RET fellow will conduct original research, and travel to scientific meetings to present his or her research during the last two years of the project. The UW Ph.D. student will also participate in the NSF-sponsored Center for Integration of Research, Training, and Learning (CIRTL) program at UW, which offers courses and coordinates internship programs that provide practical experience in bringing science to the broader community. In addition to these activities, IU will undertake a novel collaboration with the Fulbright Academy of Science and Technology (FAST) aimed at increasing public understanding about the importance of environmental microbiology. We will work with FAST to develop presentation modules that will be offered by FAST members at selected locations around the U.S. The general presentations will cover topics of current interest to the public such as the role of bacteria in the metabolism of greenhouse gases, degradation of pollutants, and nutrient cycling (specifically N and Fe) in soils and sediments.
