[Show abstract][Hide abstract] ABSTRACT: An anaerobic coculture was enriched from a hexachlorocyclohexane (HCH) polluted soil. The coculture reductively dechlorinates the beta-HCH isomer to benzene and chlorobenzene in a ratio of 0.5-2 depending on the amount of beta-HCH degraded. The culture grows with H(2) as electron donor and beta-HCH as electron acceptor, indicating that dechlorination is a respiratory process. Phylogenetic analysis indicated that the coculture consists of two bacteria that are both related to gram-positive bacteria with a low G + C content of the DNA. One bacterium was identified as a Dehalobacter sp. This bacterium is responsible for the dechlorination. The other bacterium was isolated and characterized as being a Sedimentibacter sp. This strain is not able to dechlorinate beta-HCH. The Dehalobacter sp. requires the presence of Sedimentibacter for growth and dechlorination, but the function of the latter bacterium is not clear. This is the first report on the metabolic dechlorination of beta-HCH by a defined anaerobic bacterial culture.
[Show abstract][Hide abstract] ABSTRACT: The biological anaerobic reductive dechlorination of beta-hexachlorocyclohexane under methanogenic conditions was tested in a number of contaminated soil samples from two locations in the Netherlands. Soils from a heavily polluted location showed rapid dechlorination of beta-hexachlorocyclohexane to benzene and chlorobenzene with lactate as electron donor. Soils from an adjacent slightly polluted location did not show substantial dechlorination of beta-hexachlorocyclohexane within 4 months. A heavily polluted sample was selected to optimise the dechlorination. All tested hexachlorocyclohexane isomers (alpha-, beta-, gamma-, and delta-), either added separately or simultaneously, were dechlorinated in this soil sample. The most rapid dechlorination was observed at a temperature of 30 degrees C. Dechlorination of beta-hexachlorocyclohexane was observed with acetate, propionate, lactate, methanol, H2, yeast extract and landfill leachate as electron donors. In a soil percolation column, packed with a selected heavily polluted soil sample, the presence of 10 mM sulphate in the influent led to simultaneous dechlorination of beta-hexachlorocyclohexane and sulphate reduction. When the column was fed with 10 mM nitrate instead of sulphate, dechlorination ceased immediately. After omitting nitrate from the influent, dechlorination activity recovered in about 1 month. Also in a separate column, the addition of nitrate from the start of the experiment did not result in dechlorination of beta-HCH. The significance of these experiments for in situ bioremediation of polluted soils is discussed.
[Show abstract][Hide abstract] ABSTRACT: The current knowledge on microbial reductive dechlorination of chlorinated ethenes (CEs) and its application are discussed. Physiological studies on CEs dechlorinating microorganisms indicate that a distinction can be made between cometabolic dechlorination and halorespiration. Whereas cometabolic dechlorination is a coincidental and nonspecific side reaction, catalyzed by several methanogenic and acetogenic bacteria, halorespiration is a specific enzymatic reaction from which metabolic energy can be gained. In contrast to the well-studied biological dechlorination of PCE to cis -DCE, little is known about the biology of the further dechlorination from cis -DCE to ethene. Bacteria performing the latter reaction have not yet been isolated. Microbial reductive dechlorination can be applied to the in situ bioremediation of CEs contaminated sites. From laboratory and field studies, it has become clear that the dechlorination of tetrachloroethene (PCE) to cis -clichloroethene ( cis -DCE) occurs rapidly and can be stimulated relatively easily. However, complete reduction to ethene appears to be a slower process that is more difficult to achieve.
[Show abstract][Hide abstract] ABSTRACT: A soil from a former chemical redistribution company, contaminated with mainly chlorinated aliphatics, was studied for bioremediation purposes. Groundwater analyses revealed that the original pollutants, i.e. tetrachloroethene (PCE) and trichloroethene (TCE), were present at levels ranging from 2.3 to 122 mg/L. Dichloroethene (DCE), vinylchloride (VC), ethene and ethane were also detected at significant concentrations although they had never been introduced to the soil. Relatively high concentrations of cisDCE as compared to trans-DCE and 1,1-DCE indicated that a slow in situ biodegradation had taken place by reductive dechlorination. Laboratory experiments with flow-through soil columns were performed to determine the optimal conditions for the enhancement of reductive dechlorination by the indigenous dechlorinating population. The addition of single electron donors to artificial groundwater resulted in the dechlorination of PCE to TCE and cis-DCE, whereas complete dechlorination to ethene was solely achieved with compost extract added to native groundwater.
[Show abstract][Hide abstract] ABSTRACT: A methanogenic microbial consortium capable of reductively dechlorinating 1,2,4-trichlorobenzene (1,2,4-TCB) was enriched from a mixture of polluted sediments. 1,2,4-TCB was dechlorinated via 1,4-dichlorobenzene (1,4-DCB) to chlorobenzene (CB). Lactate, which was used as an electron donor during the enrichment, was converted via propionate and acetate to methane. Glucose, ethanol, methanol, propionate, acetate, and hydrogen were also suitable electron donors for dechlorination, whereas formate was not. The addition of 5% (wt/vol) sterile Rhine River sand was necessary to maintain the dechlorinating activity of the consortium. The addition of 2-bromoethanesulfonic acid (BrES) inhibited methanogenesis completely but had no effect on the dechlorination of 1,2,4-TCB. The consortium was also able to dechlorinate other chlorinated benzenes via various simultaneous pathways to 1,3,5-TCB, 1,2-DCB, 1,3-DCB, or CB as an end product. The addition of BrES inhibited several of the simultaneously occurring dechlorination pathways of 1,2,3,4- and 1,2,3,5-tetrachlorobenzene and of pentachlorobenzene, which resulted in the formation of CB as the only final product. Hexachlorobenzene and polychlorinated biphenyls (PCBs) were dechlorinated after a lag phase of ca. 15 days, showing a dechlorination pattern that is different from those observed for lower chlorinated benzenes: only chlorines with two adjacent chlorines were removed. The results show that the consortium possesses at least three distinct dechlorination activities toward chlorinated benzenes and PCBs.
Applied and Environmental Microbiology 05/1997; 63(4):1225-9. · 3.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Biotransformation is controlled by the biochemical activity of microorganisms and the mass transfer of a chemical to the microorganisms. A generic mathematical concept for bioavailability is presented taking bath factors into account. The combined effect of mass transfer of a substance to the cell and the intrinsic activity of the cell using the substance as primary substrate, is quantified in a bioavailability number (Bn). The concept can easily be extended to secondary substrates. The approach has been applied to explain the observed kinetics of the biotransformation of organic compounds in soil slurries and in percolation columns. The model allowed us to predict threshold concentrations below which no biotransformation is possible. Depending on the environmental system and the chemical involved, predicted threshold concentrations span a range of 11 orders of magnitude from nanograms to grams per liter and match with published experimental data. Mass transfer-and not the intrinsic microbial activity-is in most cases the critical factor in bioremediation.
[Show abstract][Hide abstract] ABSTRACT: During the production of the pesticide lindane (γ-hexachlorocyclohexane; γ-HCH), large quantities of byproducts, like the α-, β-, and δ-HCH isomers, were discarded at dump sites. β-HCH was found to be extremely persistent in the environment under aerobic conditions. We studied the degradation of this isomer under methanogenic conditions in a flow-through column packed with polluted sediment. β-HCH was completely removed in this system. Chlorobenzene was detected in the effluent as a product. A β-HCH transforming anaerobic enrichment culture was obtained in batch cultures by using the column material as inoculum. δ-2,3,4,5-Tetrachlorocyclohexene is proposed as an intermediate during transformation, while benzene and chlorobenzene were formed as stable end products. The enrichment culture was also able to dechlorinate α-HCH at a comparable rate and γ- and δ-HCH at lower rates. Dechlorination was inhibited by the addition of vancomycin, but not by the addition of bromoethanesulfonic acid. Pasteurization inhibited dechlorination completely. This is the first detailed description of the biodegradation of β-HCH, including intermediate and end product identification, under defined anaerobic conditions.