Trichloroethylene (TCE) was efficiently biodegraded in situ by aerobic cometabolism at the Moffett Federal Airfield test site, in the presence of phenol or toluene (Hopkins et al. Appl. Environ. Microbiol. 1993, 59, 2277; Hopkins et al. Environ. Sci. Technol. 1993, 27, 2542; Hopkins, G. D.; McCarty, P. L. Environ. Sci. Technol. 1995, 29, 1628). Using uncontaminated soil from this site as an inoculum, a semicontinuous slurry microcosm method was developed that reproduced in situ TCE degradation rates. The slurry method was then applied to evaluate the in situ TCE biodegradation potential at Edwards Air Force Base where full-scale application was contemplated. With 0.66 mg/L TCE and either 9.7 mg/L toluene or 13.4 mg/L phenol in the exchange fluid, steady state TCE removals varied between 87 and 99%, depending upon sample depth. Toluene and phenol growth yields based upon oxygen to substrate ratios were 0.77 and 0.59 g/g during the start-up phase and 0.52 and 0.36 g/g during steady state TCE removal, respectively. The TCE degradation rate constant ratio, k c/K c, was similar for the two substrates. Steady state TCE removals varied little in a given microcosm over 1 year of operation. In the Moffett and Edwards microcosms as well as at Moffett Federal Airfield (Fries et al. Appl. Environ. Technol. 1997, 63, 1523), toluene o-monooxygenase was the dominant TCE-oxidizing enzyme present.

The initial step in the anoxic metabolism of nitrilotriacetate (NTA) was investigated in a denitrifying member of they subgroup of the Proteobacteria. In membrane-free cell extracts, the first step of NTA oxidation was catalyzed by a protein complex consisting of two enzymes, NTA dehydrogenase (NTADH) and nitrate reductase (NtrR). The products formed were iminodiacetate and glyoxylate. Electrons derived from the oxidation of NTA were transferred to nitrate only via the artificial dye phenazine methosulfate, and nitrate was stoichiometrically reduced to nitrite. NTADH activity could be measured only in the presence of NtrR and vice versa. The NTADH-NtrR enzyme complex was purified and characterized. NTADH and NtrR were both %2 dimers and had molecular weights of 170,000 and 105,000, respectively. NTADH contained covalently bound flavin cofactor, and NtrR contained a type b cytochrome. Optimum NTA-oxidizing activity was achieved at a molar ratio of NTADH to NtrR of approximately 1:1. So far, NTA is the only known substrate for NTADH. This is the first report of a redox enzyme complex catalyzing the oxidation of a substrate and concomitantly reducing nitrate.

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