Comparison of factors influencing trichloroethylene degradation by toluene-oxidizing bacteria

Abstract

The degradation of trichloroethylene (TCE) by toluene-oxidizing bacteria has been extensively studied, and yet the influence of environmental conditions and physiological characteristics of individual strains has received little attention. To consider these effects, the levels of TCE degradation by strains distinguishable on the basis of toluene and nitrate metabolism were compared under aerobic or hypoxic conditions in the presence and absence of nitrate and an exogenous electron donor, lactate. Under aerobic conditions with tolueneinduced cells, strains expressing toluene dioxygenases (Pseudomonas putida F1, Pseudomonas sp. strain JS150, Pseudomonas fluorescens CFS215, and Pseudomonas sp. strain W31) degraded TCE at low rates, with less than 12% of the TCE removed in 18 h. In contrast, strains expressing toluene monooxygenases (Burkholderia cepacia G4, Burkholderia pickettii PKO1, and Pseudomonas mendocina KR1) degraded 36 to 67% of the TCE over the same period. Under hypoxic conditions (1.7 mg of dissolved oxygen per liter) or when lactate was added as an electron donor, the extent of TCE degradation by toluene-induced cells was generally lower. In the presence of lactate, degradation of TCE by denitrifying strain PKO1 was enhanced by nitrate under conditions in which dissimilatory nitrate reduction was observed. The results of experiments performed with strains F1, G4, PKO1, and KR1 suggested that TCE or an oxidation product induces toluene degradation and that TCE induces its own degradation in the monooxygenase strains. The role of TCE as an inducer of toluene oxygenase activity in PKO1 was confirmed by performing a promoter probe analysis, in which we found that TCE activates transcription from the PKO1 3-monooxygenase operon promoter.

Degradation of mixtures of aromatic and chloroaliphatic hydrocarbons by aromatic hydrocarbon-degrading bacteria

“…The general pattern of degradation di¡ered from that of G4, PKO1, and KR1 in that more than 90% of IPB and 1,4-DCB was transformed in all cases. However, signi¢cantly less TCE was degraded than for the three monooxygenase strains, a ¢nding which is consistent with those of Leahy et al [9]. BZ, TOL, and EBZ, growth substrates for F1 and JS150 [14,31,36], were also completely or nearly completely de-graded in all cases, as was STYR.…”

“…These £asks were ¢tted with a screw-thread side-arm which was sealed with a mininert valve (Alltech Associates, Deer¢eld, IL, USA). Enrichments were initially established by suspending activated sludge (10 ml) in 100 ml of a basal salts medium (BM) [9], and injecting 1 mM hydrocarbon (nominal liquid phase concentration) directly into the suspension via the mininert valve. The cultures were incubated at 30 ‡C with shaking at 200 rpm.…”

“…In order to exploit the co-oxidation of hydrocarbons in the natural environment, a suitable hydrocarbon-degrading population or community must be present, together with a su⁄cient concentration of a carbon and energy source for protein synthesis, an electron donor to provide NADH, and an appropriate inducer to activate expression of the oxygenase genes. While some chloroaliphatics, such as TCE, may serve to induce their own metabolism [9], it may be necessary to provide a second hydrocarbon substrate, such as phenol or TOL, to stimulate the growth of TCE-degrading populations in contaminated environments [17] and to serve as an electron donor. When aromatic and chloroaliphatic hydrocarbon contaminants are present as mixtures, however, such as at hazardous waste sites [18] or in ground water contaminated by land¢ll leachates [19], it might be expected that co-oxidation reactions could be supported by the presence of aromatic hydrocarbons which can act as growth substrates and inducers.…”

Aerobic biodegradation of N‐nitrosodimethylamine (NDMA) by axenic bacterial strains

“…Interestingly, bacterial oxygenases that are active on donors such as methane, propane, ammonia, and toluene have also been shown to have the ability to oxidize xenobiotic compounds such as chlorinated aliphatic hydrocarbons (Arciero et al, 1989;Nelson et al, 1987;Tsien et al, 1989;Wackett et al, 1989) and MTBE (Deeb et al, 2001;Smith et al, 2003). In the case of trichloroethene, this oxidation reaction can be catalyzed by both monooxygenases (Leahy et al, 1996;Shields et al, 1989) and dioxygenases (Leahy et al, 1996;Nelson et al, 1988;Wackett and Gibson, 1988;Zylstra et al, 1989). The relaxed regiospecificity found in enzymes that are functionally analogous to those determined to degrade NDMA in higher organisms suggests that bacterial enzymes may have the capability to degrade NDMA.…”

Ralstonia pickettiiin environmental biotechnology: potential and applications

“…the ability of the organisms to survive toxic intermediates produced from the oxidation of TCE). PKO1 also has the ability to degrade TCE under hypoxic conditions using nitrate as an alternative electron acceptor to oxygen as with aromatic hydrocarbons (Leahy et al 1996). In recent trials, R. pickettii PKO1 achieved 83AE9% removal of TCE at a concentration of 0AE2 mg l )1 after 48 h in a hydrocarbon degradation assay (Leahy et al 2003).…”