Thomas DiChristina, Professor
About Thomas DiChristina
Ph.D., California Institute of Technology, 1989
Office: Environmental Science & Technology (ES&T) 1240
Environmental microbiology, geomicrobiology, biogeochemistry, microbial degradation of pollutants, microbial metal reduction
Our research group focuses on the molecular biology and biogeochemistry of anaerobic bacteria that inhabit marine and freshwater environments. We are interested in anaerobic bacteria that utilize transition metals (iron, manganese, uranium, selenium) as alternate terminal electron acceptors for anaerobic respiration. Bacterial metal reduction drives a wide range of environmentally important processes in the environment including the biogeochemical cycling of metals, the primary productivity of surface waters, and the biodegradation of hazardous organic pollutants, yet the molecular basis of the metal reduction process is not well understood.
Our research on the molecular basis of bacterial metal reduction includes both a genetic and biochemical component. The genetic component focuses on isolation and characterization of the genes that enable metal-reducing bacteria to respire anaerobically on metals as respiratory electron acceptor. The biochemical component focuses on isolation and characterization of the proteins that are encoded by the metal reduction genes. The goal of our future work is to generate metal reduction-specific molecular probes (oligonucleotide- and antibody-based) that can be used as ecological tools to probe anaerobic environments for the presence and activity of metal-reducing bacteria.
We are taking an interdisciplinary approach to study the biogeochemistry of two coastal salt marsh sediments (Sapelo Island, GA and the Scheldt Estuary, The Netherlands), a freshwater lake sediment (Athens, GA) and a two-mile deep marine basin (Orca Basin, Gulf of Mexico). This field-based research project is a collaborative effort with the biogeochemistry research groups of Dr. Philippe Van Cappellen (University of Utrecht, The Netherlands), and Dr. Joel Kostka (Florida State University). Our microbial group employs traditional- and 16S rRNA-based detection techniques to determine the microbial community structure at each field site, while the geochemistry groups determine the geochemical composition. A cross-comparison of results provides us with a clear picture of the major biogeochemical processes that dominate anaerobic environments.
We are also developing a new generation of scanning nanoprobe microscopic techniques for nanometer-scale imaging of biochemical processes at microbe-Fe(III) mineral interfaces. Microbial Fe(III) reduction is a relatively recent addition to the suite of anaerobic respiratory processes carried out by microorganisms and is thought to play a significant role in the global biogeochemical cycles of carbon and iron. The molecular mechanism of microbial Fe(III) reduction, however, is poorly understood. For investigation of complex chemical, biochemical and physical processes at microbe-mineral interfaces, correlation of in situ electrochemical, topographical and optical information is required. Our project fosters interactions between experts in the fields of chemistry, biochemistry, geochemistry, microbiology, fluids and mass transport, microfabrication and spectroscopy. This multi-disciplinary research team will fabricate Atomic Force Microscopy and Scanning Nearfield Optical Microscopy tips with Fe(III) reductase enzymes embedded in the cantilevers. pH nanoelectrodes and mercury/gold amalgam nanoelectrodes for Fe2+ detection will be integrated into the scanning nanoprobe tips and the microbe-mineral interface will be mapped at the nanometer scale. The multifunctional scanning nanoprobes will be used to determine the molecular mechanism of reductive dissolution of Fe(III) minerals by Fe(III)-reducing bacteria or Fe(III) chemical reductants.
Dale, J., R. Wade and T. DiChristina. 2007. A conserved histidine in cytochrome c maturation permease CcmB of Shewanella putrefaciens is required for anaerobic growth below a threshold standard redox potential. Journal of Bacteriology, 189:1036-1043.
Neal, A., S. Dublin, J. Taylor, D. Bates, J. Burns, R. Apkarian and T. DiChristina. 2007. Terminal electron acceptors influence the quantity and chemical composition of capsular exopolymers produced by anaerobically growing Shewanella. Biomacromolecules, 8:166-174.
Payne, A. and T. DiChristina. 2006. A rapid mutant screening technique for detection of technetium [Tc(VII)] reduction-deficient mutants of Shewanella oneidensis MR-1. FEMS Microbiol. Lett., 259:282-287.
DiChristina, T., D. Bates, J. Burns, J. Dale and A. Payne. 2006. Microbial metal reduction by members of the genus Shewanella: novel strategies for anaerobic respiration. In L. Neretin (ed.), Biogeochemistry of Anoxic Marine Basins. Kluwer Publ. Co.,Dordrecht, NL.
DiChristina, T., J. Fredrickson and J. Zachara. 2005. Enzymology of electron transport: Energy generation with geochemical consequences. Reviews in Mineralogy and Geochemistry, 59:27-52.
Koretsky, C., P. VanCappellen, T. DiChristina, J. Kostka, K. Lowe,C. Moore, A. Roychoudhury and E. Viollier. 2005. Salt marsh pore water geochemistry does not correlate with microbial community structure.Estuarine and Coastal Shelf Science, 62:233-251.
Koretsky, C., C. Moore, K. Lowe, C. Meile, T. DiChristina and P. VanCappellen. 2003. Seasonal oscillation of microbial iron and sulfate reduction in salt marsh sediments (Sapelo Island, GA, USA). Biogeochemistry, 64:179-203.
DiChristina, T., C. Moore and C. Haller. 2002. Dissimilatory Fe(III) and Mn(IV) reduction by Shewanella putrefaciens requires ferE, a homolog of the pulE (gspE) Type II protein secretion gene. Journal of Bacteriology, 184:142-151.
Haller, C. and T. DiChristina. 2002. Genetic approaches in bacteria with no natural genetic systems. In U.N. Streips and R.E. Yasbin (eds.), Modern Microbial Genetics II. John Wiley and Sons, New York , pp. 581-602.
Moore, C. and T. DiChristina. 2002. Metal Cycling. In G. Bitton (ed.), The Encyclopedia of Environmental Microbiology. John Wiley and Sons, New York, pp. 1902-1913.