Characterization of an Isolate That Uses Vinyl Chloride as a Growth Substrate under Aerobic Conditions

Abstract

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...

Distribution of the Coenzyme M Pathway of Epoxide Metabolism among Ethene- and Vinyl Chloride-Degrading Mycobacterium Strains

“…EaCoMT genes were not found in BLAST database searches of Mycobacterium genomes (or any other genomes) that have been completed to date, indicating that EaCoMT is specific to the alkene-assimilation pathway. It remains to be determined whether EaCoMT is involved in the VC and ethene assimilation pathways of Pseudomonas (33,34) and Nocardioides (5) strains. The EaCoMT gene primers we have developed could be used to address this question.…”

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Aerobic bacteria that grow on ethene and vinyl chloride (VC) are widely distributed in the environment and have attracted interest because of their potential applications in bioremediation and biocatalysis (5,6,11,12,32,33). The first step in ethene and VC assimilation is known to be a monooxygenase reaction yielding epoxyethane from ethene (5, 7) and chlorooxirane from VC (12, 33), but the downstream pathways are not well understood.

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“…The first step in ethene and VC assimilation is known to be a monooxygenase reaction yielding epoxyethane from ethene (5, 7) and chlorooxirane from VC (12,33), but the downstream pathways are not well understood. Our recent work (5a) has revealed that an epoxyalkane:coenzyme M (CoM) transferase (EaCoMT) enzyme is involved in epoxyethane and chlorooxirane metabolism in Mycobacterium strain JS60, a strain isolated from contaminated groundwater by enrichment on VC as the sole carbon source (5).…”

Epoxyalkane:Coenzyme M Transferase in the Ethene and Vinyl Chloride Biodegradation Pathways of Mycobacterium Strain JS60

“…In bacteria, the initial enzymatic attack on VC and ethene is similar to the reactions observed in mammalian systems, i.e., a monooxygenase catalyzes the formation of epoxyethane (ethylene oxide) from ethene and the formation of chlorooxirane (VC epoxide) from VC (18,50). The ethene monooxygenase from Mycobacterium strain E3 has been examined in some detail (19) and is a multicomponent enzyme, most likely with a binuclear iron active site similar to those of methane and propene monooxygenases (13,39).…”

Genome Sequence of the Ethene- and Vinyl Chloride-Oxidizing Actinomycete Nocardioides sp. Strain JS614

“…strain JS614 grows on ethene and VC (4) (5) and may be useful for cleaning up VC-contaminated sites (bioremediation); this is of particular interest due to the carcinogenicity and persistence of VC as a pollutant (15,26). Strain JS614 is distinguished from other VC degraders (5,7,11,30) by its high activity on VC and its unusual physiology (20). Strain JS614 can also grow on propene and butene (27), fluoroethene (28), and nicotine (9) and has been proposed as a biocatalyst for production of chiral epoxides (23).…”