Transformations of halogenated organic compounds under denitrification conditions.

Trihalomethanes, carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dibromoethane, chlorinated benzenes, ethylbenzene, and naphthalene at concentrations commonly found in surface and groundwater were incubated under anoxic conditions to study their transformability in the presence of denitrifying bacteria. None of the aromatic compounds showed significant utilization relative to sterile controls at initial concentrations from 41 to 114 micrograms/liter after 11 weeks of incubation. Of the halogenated aliphatic compounds studied, transformations of carbon tetrachloride and brominated trihalomethanes were observed after 8 weeks in batch denitrification cultures. Carbon from the decomposition of carbon tetrachloride was both assimilated into cell material and mineralized to carbon dioxide. How this was possible remains unexplained, since carbon tetrachloride is transformed to CO2 by hydrolysis and not by oxidation-reduction. Chloroform was detected in bacterial cultures with carbon tetrachloride initially present, indicating that reductive dechlorination had occurred in addition to hydrolysis. The data suggest that transformations of certain halogenated aliphatic compounds are likely to occur under denitrification conditions in the environment.     

Volatile halogenated organic compounds in European estuaries

Sources, sinks, and distribution patterns ofvolatile halogenated organic compounds (VHOC)in estuaries were investigated during 5 cruises within the BIOGEST programme. Due to their chemical and physical properties (e.g. toxicity, persistence, mobility) these compounds are of considerable environmental concern. A wide range of compounds has been identified and quantified generally ranging from 0.1 ng l^–1 to 350 ng l^–1. Insome samples extraordinarily high values up to4700 ng l^–1 were observed indicatingcontribution from anthropogenic sources.Generally, concentrations of halogenatedcompounds of anthropogenic origin dominatedthose of prevalent natural origin. Data ofselected VHOC are presented in relation tosalinity, particular organic carbon, and totalsuspended matter. Furthermore the observedconcentrations are compared with establishedwater quality regulations. Distributionpatterns of VHOC along the estuary indicatedcommon sources for specific halogenatedcompounds. Decreasing concentrations of mostVHOC along the estuary confirm that degassingto the atmosphere and dilution with sea waterare the dominating processes controlling thefate of these compounds in estuaries.     

Transformations of halogenated organic compounds under denitrification conditions

Trihalomethanes, carbon tetrachloride, 1,1,1-trichloroethane, 1,2-dibromoethane, chlorinated benzenes, ethylbenzene, and naphthalene at concentrations commonly found in surface and groundwater were incubated under anoxic conditions to study their transformability in the presence of denitrifying bacteria. None of the aromatic compounds showed significant utilization relative to sterile controls at initial concentrations from 41 to 114 micrograms/liter after 11 weeks of incubation. Of the halogenated aliphatic compounds studied, transformations of carbon tetrachloride and brominated trihalomethanes were observed after 8 weeks in batch denitrification cultures. Carbon from the decomposition of carbon tetrachloride was both assimilated into cell material and mineralized to carbon dioxide. How this was possible remains unexplained, since carbon tetrachloride is transformed to CO2 by hydrolysis and not by oxidation-reduction. Chloroform was detected in bacterial cultures with carbon tetrachloride initially present, indicating that reductive dechlorination had occurred in addition to hydrolysis. The data suggest that transformations of certain halogenated aliphatic compounds are likely to occur under denitrification conditions in the environment.     

Biodegradation of organic compounds in vadose zone and aquifer sediments.

The microbial processes that occur in the subsurface under a typical Midwest agricultural soil were studied. A 26-m bore was installed in November of 1988 at a site of the Purdue University Agronomy Research Center. Aseptic collections of soil materials were made at 17 different depths. Physical analysis indicated that the site contained up to 14 different strata. The site materials were primarily glacial tills with a high carbonate content. The N, P, and organic C contents of sediments tended to decrease with depth. Ambient water content was generally less than the water content, which corresponds to a -0.3-bar equivalent. No pesticides were detected in the samples, and degradation of added 14C-labeled pesticides (atrazine and metolachlor) was not detected in slurry incubations of up to 128 days. The sorption of atrazine and metolachlor was correlated with the clay content of the sediments. Microbial biomass (determined by direct microscopic count, viable count, and phospholipid assay) in the tills was lower than in either the surface materials or the aquifer located at 25 m. The biodegradation of glucose and phenol occurred rapidly and without a lag in samples from the aquifer capillary fringe, saturated zone, and surface soils. In contrast, lag periods and smaller biodegradation rates were found in the till samples. Subsurface sediments are rich in microbial numbers and activity. The most active strata appear to be transmissive layers in the saturated zone. This implies that the availability of water may limit activity in the profile.     

Biodegradation of organic compounds in vadose zone and aquifer sediments.

The microbial processes that occur in the subsurface under a typical Midwest agricultural soil were studied. A 26-m bore was installed in November of 1988 at a site of the Purdue University Agronomy Research Center. Aseptic collections of soil materials were made at 17 different depths. Physical analysis indicated that the site contained up to 14 different strata. The site materials were primarily glacial tills with a high carbonate content. The N, P, and organic C contents of sediments tended to decrease with depth. Ambient water content was generally less than the water content, which corresponds to a -0.3-bar equivalent. No pesticides were detected in the samples, and degradation of added 14C-labeled pesticides (atrazine and metolachlor) was not detected in slurry incubations of up to 128 days. The sorption of atrazine and metolachlor was correlated with the clay content of the sediments. Microbial biomass (determined by direct microscopic count, viable count, and phospholipid assay) in the tills was lower than in either the surface materials or the aquifer located at 25 m. The biodegradation of glucose and phenol occurred rapidly and without a lag in samples from the aquifer capillary fringe, saturated zone, and surface soils. In contrast, lag periods and smaller biodegradation rates were found in the till samples. Subsurface sediments are rich in microbial numbers and activity. The most active strata appear to be transmissive layers in the saturated zone. This implies that the availability of water may limit activity in the profile.     

Utilization rates of trace halogenated organic compounds in acetate-grown biofilms

Trace concentrations of chlorinated benzenes and chlorinated aliphatics were biotransformed by acetate-supported biofilms, the former under aerobic conditions and the latter under methanogenic conditions. The rates of transformation of the halogenated organic compounds (secondary substrates) differed from that of acetate, the primary substrate; some were higher, some were lower, and some were similar. Factors affecting the relative rates of utilization in multisubstrate systems are not known.     

Biodegradation of volatile organic compounds by five fungal species

Five fungal species, Cladosporium resinae (ATCC 34066), Cladosporium sphaerospermum (ATCC 200384), Exophiala lecanii-corni (CBS 102400), Mucor rouxii (ATCC 44260), and Phanerochaete chrysosporium (ATCC 24725), were tested for their ability to degrade nine compounds commonly found in industrial off-gas emissions. Fungal cultures inoculated on ceramic support media were provided with volatile organic compounds (VOCs) via the vapor phase as their sole carbon and energy sources. Compounds tested included aromatic hydrocarbons (benzene, ethylbenzene, toluene, and styrene), ketones (methyl ethyl ketone, methyl isobutyl ketone, and methyl propyl ketone), and organic acids ( n-butyl acetate, ethyl 3-ethoxypropionate). Experiments were conducted using three pH values ranging from 3.5 to 6.5. Fungal ability to degrade each VOC was determined by observing the presence or absence of visible growth on the ceramic support medium during a 30-day test period. Results indicate that E. lecanii-corni and C. sphaerospermum can readily utilize each of the nine VOCs as a sole carbon and energy source. P. chrysosporium was able to degrade all VOCs tested except for styrene under the conditions imposed. C. resinae was able to degrade both organic acids, all of the ketones, and some of the aromatic compounds (ethylbenzene and toluene); however, it was not able to grow utilizing benzene or styrene under the conditions tested. With the VOCs tested, M. rouxiiproduced visible growth only when supplied with n-butyl acetate or ethyl 3-ethoxypropionate. Maximum growth for most fungi was observed at a pH of approximately 5.0. The experimental protocol utilized in these studies is a useful tool for assessing the ability of different fungal species to degrade gas-phase VOCs under conditions expected in a biofilter application.     

Transformations of 1- and 2-carbon halogenated aliphatic organic compounds under methanogenic conditions.

Several 1- and 2-carbon halogenated aliphatic organic compounds present at low concentrations (less than 100 micrograms/liter) were degraded under methanogenic conditions in batch bacterial cultures and in a continuous-flow methanogenic fixed-film laboratory-scale column. Greater than 90% degradation was observed within a 2-day detention time under continuous-flow methanogenic conditions with acetate as a primary substrate. Carbon-14 measurements indicated that chloroform, carbon tetrachloride, and 1,2-dichloroethane were almost completely oxidized to carbon dioxide, confirming removal by biooxidation. The initial step in the transformations of tetrachloroethylene and 1,1,2,2-tetrachloroethane to nonchlorinated end products appeared to be reductive dechlorination to trichloroethylene and 1,1,2-trichloroethane, respectively. Transformations of the brominated aliphatic compounds appear to be the result of both biological and chemical processes. The data suggest that transformations of halogenated aliphatic compounds can occur under methanogenic conditions in the environment.     

Biotransformation of halogenated compounds

As a result of natural production and contamination of the environment by xenobiotic compounds, halogenated substances are widely distributed in the biosphere. Concern arises as a result of the toxic, carcinogenic, and potential teratogenic nature of these substances. The biotransformations of such halogenated substances are reviewed, with particular emphasis on the biocatalytic cleavage of the carbon-halogen bonds. The physiology, biochemistry, and genetics of the biological system involved in the dehalogenation reactions are discussed for three groups of organohalogens: (1) the haloacids, (2) the haloaromatics, and (3) the haloalkanes. Finally, the biotechnological applications of these microbial transformations are discussed. This includes prospects for their future application in biosynthetic processes for the synthesis of halogenated intermediates or novel compounds and also the use of such systems for the detoxification and degradation of environmental pollutants.     

Biodegradation of low-molecular-weight halogenated hydrocarbons by methanotrophic bacteria

Abstract Low-molecular-weight halogenated hydrocarbons are susceptible to degradation by anaerobic and aerobic bacteria. The methanotrophic bacterium Methylosinus trichosporium 0B3b degrades trichloroethylene more rapidly than other bacteria examined to date. Expression of soluble methane monooxygenase (MMO) is correlated with high rates of biodegradation.
An analysis of 16 S rRNA sequences of 11 ribosomal RNAs from type I, type II and type X methanotrophs and methanol-utilizing bacteria have revealed four clusters of phytogenetically related methylotrophs. This information may be useful for the identification and enumeration of methylotrophs in bioreactors and other environments during remediation of contaminated waters.     

Biodegradation of low-molecular-weight halogenated hydrocarbons by methanotrophic bacteria

Low-molecular-weight halogenated hydrocarbons are susceptible to degradation by anaerobic and aerobic bacteria. The methanotrophic bacterium Methylosinus trichosporium 0B3b degrades trichloroethylene more rapidly than other bacteria examined to date. Expression of soluble methane monooxygenase (MMO) is correlated with high rates of biodegradation. An analysis of 16 S rRNA sequences of 11 ribosomal RNAs from type I, type II and type X methanotrophs and methanol-utilizing bacteria have revealed four clusters of phylogenetically related methylotrophs. This information may be useful for the identification and enumeration of methylotrophs in bioreactors and other environments during remediation of contaminated waters.     

Degradation of halogenated aromatic compounds

Due to their persistence, haloaromatics are compounds of environmental concern. Aerobically, bacteria degrade these compounds by mono- or dioxygenation of the aromatic ring. The common intermediate of these reactions is (halo)catechol. Halocatechol is cleaved either intradiol (ortho-cleavage) or extradiol (meta-cleavage). In contrast to ortho-cleavage, meta-cleavage of halocatechols yields toxic metabolites. Dehalogenation may occur fortuitously during oxygenation. Specific dehalogenation of aromatic compounds is performed by hydroxylases, in which the halo-substituent is replaced by a hydroxyl group. During reductive dehalogenation, haloaromatic compounds may act as electron-acceptors. Herewith, the halosubstituent is replaced by a hydrogen atom.Abbreviations CBz chlorobenzene - DCBz dichlorobenzene - TrCBz trichlorobenzene - TCBz tetrachlorobenzene - PCBz pentachlorobenzene - HCBz hexachlorobenzene - CBA chlorobenzoic acid - BBA bromobenzoic acid - FBA fluorobenzoic acid - IBA iodobenzoic acid - CP chlorophenol - CA chloroaniline - PCBs polychlorinated biphenyls - CB chlorobiphenyl - 2,4-D 2,4-dichlorophenoxyacetic acid - 2,4,5-T 2,4,5-trichlorophenoxyacetic acid     

Transformations of 1- and 2-carbon halogenated aliphatic organic compounds under methanogenic conditions

Several 1- and 2-carbon halogenated aliphatic organic compounds present at low concentrations (less than 100 micrograms/liter) were degraded under methanogenic conditions in batch bacterial cultures and in a continuous-flow methanogenic fixed-film laboratory-scale column. Greater than 90% degradation was observed within a 2-day detention time under continuous-flow methanogenic conditions with acetate as a primary substrate. Carbon-14 measurements indicated that chloroform, carbon tetrachloride, and 1,2-dichloroethane were almost completely oxidized to carbon dioxide, confirming removal by biooxidation. The initial step in the transformations of tetrachloroethylene and 1,1,2,2-tetrachloroethane to nonchlorinated end products appeared to be reductive dechlorination to trichloroethylene and 1,1,2-trichloroethane, respectively. Transformations of the brominated aliphatic compounds appear to be the result of both biological and chemical processes. The data suggest that transformations of halogenated aliphatic compounds can occur under methanogenic conditions in the environment.     

Biodegradation of aromatic compounds by Escherichia coli.

Although Escherichia coli has long been recognized as the best-understood living organism, little was known about its abilities to use aromatic compounds as sole carbon and energy sources. This review gives an extensive overview of the current knowledge of the catabolism of aromatic compounds by E. coli. After giving a general overview of the aromatic compounds that E. coli strains encounter and mineralize in the different habitats that they colonize, we provide an up-to-date status report on the genes and proteins involved in the catabolism of such compounds, namely, several aromatic acids (phenylacetic acid, 3- and 4-hydroxyphenylacetic acid, phenylpropionic acid, 3-hydroxyphenylpropionic acid, and 3-hydroxycinnamic acid) and amines (phenylethylamine, tyramine, and dopamine). Other enzymatic activities acting on aromatic compounds in E. coli are also reviewed and evaluated. The review also reflects the present impact of genomic research and how the analysis of the whole E. coli genome reveals novel aromatic catabolic functions. Moreover, evolutionary considerations derived from sequence comparisons between the aromatic catabolic clusters of E. coli and homologous clusters from an increasing number of bacteria are also discussed. The recent progress in the understanding of the fundamentals that govern the degradation of aromatic compounds in E. coli makes this bacterium a very useful model system to decipher biochemical, genetic, evolutionary, and ecological aspects of the catabolism of such compounds. In the last part of the review, we discuss strategies and concepts to metabolically engineer E. coli to suit specific needs for biodegradation and biotransformation of aromatics and we provide several examples based on selected studies. Finally, conclusions derived from this review may serve as a lead for future research and applications.     

Biodegradation kinetics of volatile hydrophobic organic compounds in cultures with variable fractional volumes

An extension of the models developed by Guha and Jaffé (Biotechnol Bioeng [1996] 50:693-699) to describe the phenanthrene biodegradation kinetics for the cultures with variable fractional volumes is presented. Batch experiments were conducted with a culture capable of degrading the phenanthrene using a single culture vessel from which samples were withdrawn over time to monitor the disappearance of phenanthrene. For accurate measurement of phenanthrene concentrations, a sampling procedure designed for quantifying the sorption of phenanthrene onto glassware was also introduced. The Monod parameters were estimated by nonlinear regression analyses of simultaneous solutions to the substrate utilization/volatilization and Monod equations for growth of the cell mass. The results demonstrate that the models were able to be extended to phenanthrene-degrading cultures with variable fractional volumes. When the ratio between sampling volume and volume of the culture medium was relatively small, the parameters obtained were similar to those which would be obtained using constant fractional volumes of culture medium. It was also found that the model's fit to the phenanthrene disappearance data in this study were better than those obtained by Guha and Jaffé, implying that the sorption process of phenanthrene during the sampling period could significantly affect the measurement of phenanthrene concentrations. Failing to account for these losses led to less accurate measurements of substrate concentrations, which in turn resulted in a poor estimation of the parameters. The findings of this study reduce considerably the experimental work necessary in the estimation of Monod kinetic parameters for the purpose of modeling.     

Anaerobic degradation of halogenated aromatic compounds

Recent microbiological findings show how compounds, regarded hitherto as unusual substrates for anaerobic bacteria, are degraded under anaerobic conditions. The complete conversion of halobenzoic acids and halophenolic compounds to methane by lake sediment and sewage sludge microorganisms has been demonstrated. Since haloaromatic compounds are widely used and may be found in such effluents as those from the forest industry, these studies could stimulate a broader interest in anaerobic treatment of industrial waste waters which contain unusual organic compounds.