An aerobic enrichment culture was developed by using vinyl chloride (VC) as the sole organic carbon and electron donor source. VC concentrations as high as 7.3 mM were biodegraded without apparent inhibition. VC use did not occur when nitrate was provided as the electron acceptor. A gram-negative, rod-shaped, motile isolate was obtained from the enrichment culture and identified based on biochemical characteristics and the sequence of its 16S rRNA gene as Pseudomonas aeruginosa, designated strain MF1. The observed yield of MF1 when it was grown on VC was 0.20 mg of total suspended solids (TSS)/mg of VC. Ethene, acetate, glyoxylate, and glycolate also served as growth substrates, while ethane, chloroacetate, glycolaldehyde, and phenol did not. Stoichiometric release of chloride and minimal accumulation of soluble metabolites following VC consumption indicated that the predominant fate for VC is mineralization and incorporation into cell material. MF1 resumed consumption of VC after at least 24 days when none was provided, unlike various mycobacteria that lost their VC-degrading ability after brief periods in the absence of VC. When deprived of oxygen for 2.5 days, MF1 did not regain the ability to grow on VC, and a portion of the VC was transformed into VC-epoxide. Acetylene inhibited VC consumption by MF1, suggesting the involvement of a monooxygenase in the initial step of VC metabolism. The maximum specific VC utilization rate for MF1 was 0.41 mol of VC/mg of TSS/day, the maximum specific growth rate was 0.0048/day, and the Monod half-saturation coefficient was 0.26 M. A higher yield and faster kinetics occurred when MF1 grew on ethene. When grown on ethene, MF1 was able to switch to VC as a substrate without a lag. It therefore appears feasible to grow MF1 on a nontoxic substrate and then apply it to environments that do not exhibit a capacity for aerobic biodegradation of VC.Contamination of groundwater with vinyl chloride (VC) occurs primarily via anaerobic reductive dechlorination of tetrachloroethene, trichloroethene, and 1,1,1-trichloroethane (45). The maximum contaminant level for VC in drinking water is 2 g/liter, which is lower than for any other volatile organic compound (34). This is consistent with the fact that VC is a known human carcinogen. Reductive dechlorination of VC to ethene (11, 16) and anaerobic oxidation of VC under ironreducing and methanogenic conditions (4, 6) often occur at relatively low rates. The potential for persistence of VC has long been a concern with the exclusive reliance on anaerobic dechlorination as a method for groundwater remediation.In contrast, it is generally accepted that VC is readily biodegradable under aerobic conditions. Cometabolism of VC has been demonstrated with numerous primary substrates, including ethene (17, 28), ethane (17), methane (8, 12), propane (30, 32), propylene (14), isoprene (15), 3-chloropropanol (8), and ammonia (37, 44). Under such conditions, cometabolism of VC occurs faster and with less apparent toxicity than cometabolism of more chlori...

Pseudomonas aeruginosa strain DL1 was isolated on ethene as a sole carbon and energy source. When ethene-grown DL1 was first exposed to vinyl chloride (VC), the rate of VC consumption was very rapid and then declined sharply, indicative of a cometabolic process. A lack of growth and significant release of soluble products during this interval also indicates that the initial activity on VC was cometabolic. Following the rapid initial rate of VC cometabolism, a slow rate of VC utilization continued. After an extended period of incubation (>40 days), a transition occurred that allowed DL1 to begin using VC as a primary growth substrate, with an observed yield, maximum growth rate, and Monod half saturation coefficient of 0.21 mg of total suspended solids/mg VC, 0.046 d(-1), and 1.17 microM VC, respectively, at 22 degrees C. Acetylene inhibits consumption of ethene and VC by ethene-grown cells, suggesting a monooxygenase is responsible for initiating metabolism of these alkenes. Resting cells grown on ethene cometabolized VC with an observed transformation capacity of 9.1 micromol VC/mg total suspended solids and a transformation yield of 0.22 mol VC/mol ethene. The presence of 40 microM ethene increased the rate and amount of VC cometabolized. However, consumption of higher concentrations of ethene decreased the total amount of VC consumed, and VC inhibited ethene utilization. A kinetic model was developed that describes substrate interactions during batch depletion of ethene and VC for a range of initial concentrations. The results suggest that ethene may stimulate in situ biodegradation of VC either by functioning as a primary substrate to support cometabolism of VC or by selecting for organisms that can utilize VC as a primary substrate.

d 1,2-Dichloroethane (1,2-DCA) and 1,2-dibromoethane (ethylene dibromide [EDB]) contaminate groundwater at many hazardous waste sites. The objectives of this study were to measure yields, maximum specific growth rates ( ), and half-saturation coefficients (K S ) in enrichment cultures that use 1,2-DCA and EDB as terminal electron acceptors and lactate as the electron donor and to evaluate if the presence of EDB has an effect on the kinetics of 1,2-DCA dehalogenation and vice versa. Biodegradation was evaluated at the high concentrations found at some industrial sites (>10 mg/liter) and at lower concentrations found at former leaded-gasoline sites (1.9 to 3.7 mg/liter). At higher concentrations, the Dehalococcoides yield was 1 order of magnitude higher when bacteria were grown with 1,2-DCA than when they were grown with EDB, while 's were similar for the two compounds, ranging from 0.19 to 0.52 day ؊1 with 1,2-DCA to 0.28 to 0.36 day ؊1 for EDB. K S was larger for 1,2-DCA (15 to 25 mg/ liter) than for EDB (1.8 to 3.7 mg/liter). In treatments that received both compounds, EDB was always consumed first and adversely impacted the kinetics of 1,2-DCA utilization. Furthermore, 1,2-DCA dechlorination was interrupted by the addition of EDB at a concentration 100 times lower than that of the remaining 1,2-DCA; use of 1,2-DCA did not resume until the EDB level decreased close to its maximum contaminant level (MCL). In lower-concentration experiments, the preferential consumption of EDB over 1,2-DCA was confirmed; both compounds were eventually dehalogenated to their respective MCLs (5 g/liter for 1,2-DCA, 0.05 g/liter for EDB). The enrichment culture grown with 1,2-DCA has the advantage of a more rapid transition to 1,2-DCA after EDB is consumed.

Intrinsic biodegradation of trichloroethene and 1,1,1-trichloroethane in groundwater at a Superfund site in California has been observed. An anaerobic zone exists in the area closest to the source location, yielding the expected complement of reductive dechlorination daughter products, including cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC). Significant levels of methane and ethene were also generated in the anaerobic zone. The groundwater returns to aerobic conditions downgradient of the source, with methane, ethene, VC, and several other compounds still present. Attenuation of VC in the aerobic zone suggests that it is being biodegraded. In this study microcosms were used to evaluate the role of methane and ethene as primary substrates for aerobic biodegradation of VC. Biodegradation of VC was fastest in the bottles containing ethene, with 40 mumol of VC consumed over a 150 day period, compared to approximately 15-20 mumol with methane or a mixture of methane and ethene. VC did not noticeably inhibit ethene biodegradation but did slow the rate of methane use. Methane inhibited ethene metabolism, which apparently caused a reduction in VC biodegradation when methane was present with ethene. These results suggest that ethene plays an important role during in situ natural attenuation of VC under aerobic conditions. Microcosms were also set up with VC alone. Following a 75 day lag period. VC consumption began and subsequent additions were consumed without a lag, suggesting the presence of organisms capable of using VC as a growth substrate. After providing VC alone for nearly 400 days, aliquots of the enrichment culture were used to evaluate its ability to biodegrade cis- and trans-DCE. Both compounds were readily consumed, although addition of VC as the primary substrate was needed to sustain biodegradation of repeated additions. This result suggests that organisms capable of using VC as a sole substrate may play an active role in aerobic natural attenuation of DCEs.

An aerobic enrichment culture was grown on vinyl chloride (VC) as the sole source of carbon and energy. In the absence of VC, the enrichment culture cometabolized cis-1,2-dichloroethene (cDCE) and, to a lesser extent, trans1,2-dichloroethene (tDCE), beginning with oxidation to the corresponding DCE-epoxides. When provided with VC (1.3 mM) and cDCE (0.2-0.3 mM), the enrichment culture cometabolized repeated additions of cDCE for over 85 days. Cometabolism of repeated additions of tDCE was also demonstrated but at a lower ratio of nongrowth substrate to VC. VC-grown Pseudomonas aeruginosa MF1 (previously isolated from the enrichment culture) also readily cometabolizes cDCE, with an observed transformation capacity (Tc,obs) of 0.82 micromol of cDCE/mg of total suspended solids (TSS). When provided with VC and cDCE, MF1 did not begin cometabolizing cDCE until nearly all of the VC was consumed. The presence of cDCE reduces the maximum specific rate of VC utilization. A kinetic model was developed that describes these phenomena via Monod parameters for substrate and nongrowth substrate, plus inactivation and inhibition coefficients. MF1 did not show any cometabolic activity on tDCE or trichloroethene and very limited activity on 1,1-DCE (Tc,obs = 2 x 10(-5) micromol/mg TSS). Above 40 microM, tDCE and TCE noticeably increased the maximum specific rate of VC utilization, even though neither compound was consumed during or after VC consumption. High concentrations of 1,1-DCE (950 microM) completely inhibited VC biodegradation. As there is currently no evidence for aerobic biodegradation of cDCE as a sole source of carbon and energy, the results of this study provide a potential explanation for in situ disappearance of cDCE when the only other significant substrate available is VC. It is fortuitous that the VC-grown cultures tested exhibit their highest cometabolic activity toward cDCE, because it is the predominant DCE isomer formed during anaerobic reductive dechlorination of trichloroethene and tetrachloroethene.