Research Interests

Microbial Uranium Bioimmoblization

Nuclear weapons production began in the early 1940’s and continued through the Cold War Era (early 1990’s) and required the mining, milling, and enrichment of uranium-235. Production of uranium-235 resulted in widespread environmental contamination across North America, South America, and Eastern Europe.

In the U.S. alone, the Department of Energy (DOE) is responsible for the remediation of > 7,280 km2 of soils and groundwater contaminated due to processes associated with uranium extraction for nuclear weapons production. Oxidized uranium, U(VI), is highly soluble, chemically toxic, radioactive, and is a potential contaminant to local drinking water reservoirs. Therefore, the U.S. DOE formed the Environmental Remediation Sciences Program (ERSP) to support scientific research for developing cost-effective methods for the remediation of uranium-contaminated sites.
Bioremediation, the use of living organisms to reduce, eliminate, or contain hazardous contaminants, is one of the most promising strategies for the long-term stewardship of uranium at DOE sites. The goal of uranium bioremediation is to immobilize contaminants in situ by stimulating indigenous microorganisms biologically reduce soluble U(VI) to insoluble U(IV).

The goal of my dissertation research was to provide an understanding of microbial community dynamics in uranium-contaminated subsurface sediments. I primarily worked with sediments from the U.S. DOE’s Oak Ridge Field Research Center (ORFRC), located adjacent to the Y-12 industrial complex, in Oak Ridge, TN. The ORFRC site is contaminated with waste products from uranium enrichment processes at the Y-12 complex, which were collected and stored in three unlined ponds until 1988 when the ponds were pumped and capped by a parking lot. Subsurface groundwater flow created a contaminant plume originating from the pond site, that currently extends approximately 7 km east and west of the ponds to a depth of >150 m.
For my research, I have used an interdisciplinary approach, employing microbiological and geochemical techniques, to link the structure and function of microbial communities in contaminated subsurface sediments. I have used microcosm incubations to monitor microbial activity during bioremediation and coupled the observed geochemistry with microbial community analysis.

Microbial community analysis was performed by combining cultivation- dependent and cultivation-independent molecular techniques. Throughout my dissertation I have characterized microbial communities by targeting SSU rRNA genes using PCR, RT-PCR, cloning and sequencing, stable isotope probing (SIP), terminal restriction fragment length polymorphism (TRFLP) analysis, and quantitative PCR.
My work was performed under DOE grants of Dr. Joel Kostka and in collaboration with Dr. Joseph Stucki (Univ. Illinois), Dr. Anthony Palumbo (Oak Ridge National Lab), Dr. Kirsten Küsel (Friedrich-Schiller University Jena), Dr. Kuki Chin (Georgia State Univ.), and Dr. Lee Kerkhof (Rutgers Univ.). Please see my publications page for more details on my research. My hope is that my research can be used in future development of effective U(VI) bioremediation strategies by enhancing our current understanding of the composition, metabolic potential and physiological requirements of in situ microbial communities.

As an addition to my work at the ORFRC, I spent a summer as a guest scientist in the lab of Dr. Kirsten Küsel at the Friedrich-Schiller University Jena, Germany. My work in her lab, in conjunction with Janna Sitte and Eva-Maria Burkhardt, focused on the biogeochemistry of microbial communities in surficial soils contaminated with radionuclides and heavy metals. Our site was within the former Ronneburg Mining District, an area that was heavily mined for uranium from 1946-1990.
Much of the Ronneburg Mining District has now been remediated but groundwater runoff from a former leaching heap has contaminated the water and soils of a nearby creek. Our research was focused on identify the active microorganisms present in the acidic, heavy metal contaminated soils of the contaminated creek. We are also interested in understanding the role of microbial community activity on heavy metal mobilization. This work is still in progress and will be a part of both Janna and Eva's PhD dissertations.

Pitcher Plant Microbial Ecology

Sarracenia purpurea, commonly known as the purple pitcher plant, is a carnivorous plant native to North America. It is one of the few carnivorous plants that is inhabits cold temperate climates. The leaves of S. purpurea fill with rainwater soon after opening and supports a diverse aquatic community. The aquatic environment within the leaves provides a unique habitat for studying food web interactions and the abiotic and biotic factors controlling the success of invasive species. The aquatic communities within the leaves of S. purpurea have been extensively studied by Dr. Thomas Miller, FSU Biology, and Sarah Gray, PhD candidate at Stonybrook University. However, little work has been performed to characterize the total and metabolically active microbial communities in the water of S. purpurea leaves.
In the summer of 2008, I started a project with Sarah, Tom, and Mike Humphrys to determine the composition and diversity of the microbial community present in the water of the pitcher plant Sarracenia purpurea using cultivation-independent techniques. We collected water from the leaves of pitcher plants in the Apalachicola National Forest in the Florida panhandle and we are currently using molecular techniques to identify the microbial populations within the leaves. Our work is in progress and hope to have exciting results soon.