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Gary Sayler, Ph.D.
Professor & Director
Center for Environmental Biotechnology
UT Knoxville |
Gary S. Sayler, Professor of Microbiology and Ecology and Evolutionary Biology, is the director of the CEB. Dr. Sayler has 25 years of experience in multidisciplinary laboratory and field environmental research and biodegradation of organic pollutants such as polynuclear aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), and trichloroethylene (TCE). Over the past 15 years, he has pioneered the development of environmental molecular diagnostics including the extraction and analysis of nucleic acids from soils (a patented process), bioluminescent reporter technology, and the first field release of a genetically-engineered microorganism for remediation purposes. This research has resulted in over 200 technical publications and monographs and over 150 invited presentations at the national and international level. He is a member of five professional societies and currently serves on five editorial boards.
Research Interests
- Ecological and toxicological impact of environmental contaminants on microbial communities; biodegradative mechanisms,plasmids and transposons.
- Application of molecular methods in analysis of biodegradative microbial community structure and function. Genetic engineering strategies for biodegradative and biosensing organisms.
Presentation Description
Critical Gene Frequencies and Populations to Sustain PAH Degradation
Polycyclic Aromatic Hydrocarbons (PAH) demonstrating low solubility and high sorptive partitioning are relatively poor substrates to support microbial growth. Yet, over the past three decades many organisms have been isolated that are found to degrade low molecular weight PAH and more recent information has provided insight into the biochemical, enzymatic, and molecular basis for biodegradation of a limited range of higher molecular weight PAH substrates.
In uncontaminated aerobic soils and surface sediments, added PAH mineralize slowly with pseudo first order rate constants (k1) ranging from 3x10-4 h-1, 1x10-4 h-1 and 4x10-8 h-1, respectively for naphthalene, phenanthrene and benz(a)pyrene; increasing by an order of magnitude following prolonged exposure (60 days). Comparatively, chronically contaminated soils and sediments demonstrate mineralization rates orders of magnitude faster. Collectively, these results indicate both the presence of indigenous PAH degrading microbial communities in uncontaminated soils and the adaptation and acclimation of these communities following selection and enrichment by long term PAH exposure. The genotypic and phenotypic composition and distributions of PAH degrading populations in these communities can be key determinants in natural environmental fate processes for PAH and the success of bioremediation technology for PAH. To understand the ecological processes controlling PAH biodegradation and to monitor and optimize bioremediation technologies, molecular tools have become essential in diagnosing the capacity of the environment for natural attenuation and to measure and predict dynamic changes in specific catabolic genes and their activity in situ. In this regard, luxCDABE transcriptional fusions with the nah genes have been developed and successfully used in recombinant strain release studies to monitor and control PAH degradation in soil. Nucleic acid extraction (both DNA and mRNA) from soils, sediments and waste materials along with reverse transcriptase-PCR have been used to sample the metagenome of contaminated and uncontaminated environments and to quantify the distribution and activity of PAH biodegradative genes nahAc, nagAc and nidA (encoding ring hydroxylating dioxygenases) as correlated with degradation of both low and high molecular weight PAH. Phylogenetic analysis conducted in parallel using 16S rRNA gene sequence analysis has provided insight into the co-occurrence of members of the alpha and gamma protebacteria along with Mycobacteria involved in PAH degradation and has also shown the dominance of individual groups based on contamination history, ecological niche, and specific PAH substrates.
Advances in expression array, gene chip and high throughput sequencing technology, and the growth of large data bases and computational tools, are making molecular diagnostic approaches for site assessment, and biodegradation process monitoring and control both technically feasible and more economical. This growing capability is particularly important for persistent and toxic organic pollutants for which the biochemical capacity of biodegradation is confined to a limited number of genotypes.
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