Research in our laboratory focuses on the determinants of biodegradability of xenobiotic compounds. The model system that is currently being investigated in detail is a study of mechanisms governing regulation of metabolic diversity for degradation of benzene, toluene, ethylbenzene, and xylenes (collectively designated BTEX), as well as the chlorinated solvents perchloroethylene (PCE) and trichloroethylene (TCE). These compounds have been chosen as model substrates because of their ubiquity as groundwater contaminants in the Unites States, and because they are a primary target of federal and state regulations aimed at aquifer restoration owing to their potential negative impact on human health.
The results of the past several years of research have led us to the conclusion that bacteria such as Ralstonia pickettii PKO1 are representative of a group of bacterial strains which, from our work to date, appear to be largely indistinguishable from closely related species by previous criteria, but which have evolved a suite of adaptive traits that allow for growth and oxygen metabolism in oxygen-limited environments. These adaptive traits include the ability to carry out significant nitrate-dependent degradation of aromatic hydrocarbons under conditions of oxygen limitation; the presence of key catabolic enzymes with kinetic characteristics that allow for effective turnover of limiting substrates; and transcriptional enhancement of promoters of key catabolic operons linked to the onset of denitrification. Such results have led us to advance the hypothesis that uniquely adapted bacteria are capable of degrading aromatic hydrocarbons in hypoxic aquifer environments by a physiological strategy of "oxygen sparing", in which aerobic nitrate respiration allows for utilization of low residual levels of oxygen for critical substrate oxygenase reactions. The immediate goal of this research is to further elucidate this adaptive strategy of microbial utilization of mixed electron acceptors from the perspective of "global regulation" of catabolic operons encoding critical aromatic oxygenases. A longer range goal is to assess the functional role of such bacteria as components of complex microbial communities, with particular emphasis on their adaptation towards functionality in oligotrophic, oxygen-variable environments.
In addition to our major research focus. described above, my laboratory is actively involved in two additional research projects: (1.) microbial characterization (using group-specific, fluorescently-labeled rRNA-targeted oligonucleotide probe analysis, FAME and TTGE analysis, and T-RFLP analysis) of an MTBE-degrading consortium which is capable of mineralizing the gasoline oxygenate, methyl tert-butyl ether (MTBE); and (2.) biodegradability studies of mixed polynuclear aromatic hydrocarbons (PAH) from tar-contaminated soils at former manufactured gas plant sites, in which a combined advanced chemical oxidation/biodegradation system is being investigated for treatment of tar residues.