Showing papers on "Microbial biodegradation published in 1998"

Biodegradation of the Acetanilide Herbicides Alachlor, Metolachlor, and Propachlor

Abstract: Alachlor, metolachlor, and propachlor are detoxified in biological systems by the formation of glutathione-acetanilide conjugates. This conjugation is mediated by glutathione-S-transferase, which is present in microorganisms, plants, and mammals. Other organic sulfides and inorganic sulfide also react through a nucleophilic attack on the 2-chloro group of acetanilide herbicides, but the products are only partially characterized. Sorption in soils and sediments is an important factor controlling the migration and bioavailability of these herbicides, while microbial degradation is the most important factor in determining their overall fate in the environment. The biodegradation of alachlor and metolachlor is proposed to be only partial and primarily cometabolic, and the ring cleavage seems to be slow or insignificant. Propachlor biodegradation has been reported to proceed to substantial (> 50%) mineralization of the ring structure. Reductive dechlorination may be one of the initial breakdown mechanisms under anaerobic conditions. Aerobic and anaerobic transformation products vary in their polarity and therefore in soil binding coefficient. A catabolic pathway for chloroacetanilide herbicides has not been presented in the literature because of the lack of mineralization data under defined cultural conditions.

Metal Toxicity Reduction in Naphthalene Biodegradation by Use of Metal-Chelating Adsorbents

Abstract: A model system comprising microbial degradation of naphthalene in the presence of cadmium has been developed to evaluate metal toxicity associated with polyaromatic hydrocarbon biodegradation and its reduction by the use of unmodified and surfactant-modified clays in comparison with a commercially available chelating resin (Chelex 100; Bio-Rad). The toxicity of cadmium associated with naphthalene biodegradation was shown to be reduced significantly by using the modified-clay complex and Chelex resin, while unmodified clay has no significant impact on this reduction. The degree of metal toxicity reduction can be quantitatively related to the metal adsorption characteristics of these adsorbents, such as adsorption capacity and selectivity.

19F NMR study on the biodegradation of fluorophenols by various Rhodococcus species

Abstract: Of all NMR observable isotopes 19F is the one perhaps most convenient for studies on biodegradation of environmental pollutants. The reasons underlying this potential of 19F NMR are discussed and illustrated on the basis of a study on the biodegradation of fluorophenols by four Rhodococcus strains. The results indicate marked differences between the biodegradation pathways of fluorophenols among the various Rhodococcus species. This holds not only for the level and nature of the fluorinated biodegradation pathway intermediates that accumulate, but also for the regioselectivity of the initial hydroxylation step. Several of the Rhodococcus species contain a phenol hydroxylase that catalyses the oxidative defluorination of ortho-fluorinated di- and trifluorophenols. Furthermore, it is illustrated how the 19F NMR technique can be used as a tool in the process of identification of an accumulated unknown metabolite, in this case most likely 5-fluoromaleylacetate. Altogether, the 19F NMR technique proved valid to obtain detailed information on the microbial biodegradation pathways of fluorinated organics, but also to provide information on the specificity of enzymes generally considered unstable and, for this reason, not much studied so far.

Microbial degradation of hydrocarbons in soil during aerobic/anaerobic changes and under purely aerobic conditions

Abstract: Microbial hydrocarbon degradation in soil was studied during periodical aerobic/anaerobic switching and under purely aerobic conditions by using a pilot-scale plant with diesel-fuel-contaminated sand. The system worked according to the percolation principle with controlled circulation of process water and aeration. Periodical switching between 4 h of aerobic and 2 h of anaerobic conditions was achieved by repeated saturation of the soil with water. Whatever the cultivation mode, less than 50% of the diesel was degraded after 650 h because the hydrocarbons were adsorbed. Contrary to expectations, aerobic/anaerobic changes neither accelerated the rate of degradation nor reduced the residual hydrocarbon content of the soil. Obviously the pollutant degradation rate was determined mainly by transport phenomena and less by the efficiency of microbial metabolism. The total mass of oxygen consumed and carbon dioxide produced was greater under aerobic/anaerobic changing than under aerobic conditions, although the mass of hydrocarbons degraded was nearly the same. As shown by an overall balance of microbial growth and by a carbon balance, the growth yield coefficient was smaller during aerobic/anaerobic changes than under aerobic conditions.

Vanadium as an Internal Marker To Evaluate Microbial Degradation of Crude Oil

Abstract: 17α,21β-Hopane is used as an internal marker to evaluate the biodegradation and/or weathering of petroleum products. In this study, vanadium, the most abundant heavy metal in crude oil, was investi...

Comparison of toxicity detected by five bioassays during bioremediation of diesel fuel-spiked soils

Abstract: Biodegradation of petroleum contaminants is an effective and generally inexpensive approach for reducing their concentrations in soils. However, little information is available on the toxicological status of contaminated soils and the fate of target hydrocarbons following bioremediation. Four texturally distinct soils were contaminated with diesel fuel and bioremediated in microcosms at 22°C, with moisture contents of 85% of soil water holding capacity, and nitrogen (N) and/or phosphorus (P) nutrient amendments. The progress of bioremediation was monitored using chemical and toxicological analyses. Soil toxicity was measured using five short-term bioassays: seed germination, red blood cell hemolysis, solid-phase Microtox, SOS-chromotest, and Toxi-chromotest. Reductions in target compound concentration were not always predictive of reductions in soil toxicity. Conflicting trends were indicated by the toxicity test results. For example, total petroleum hydrocarbon analysis revealed decreased hydrocarbon concentrations in all four soils following bioremediation but seed germination and seedling emergence data indicated increased soil toxicity. In contrast, the Microtox test data indicated decreased toxicity in two of the four soils. These results suggest that measurements of target contaminant concentrations should be complemented with several different soil toxicity bioassays, particularly when evaluating the ability of bioremediation to reduce the adverse effects of contaminants in soil. © 1998 John Wiley & Sons, Inc. Environ Toxicol Water Qual 13: 117–126, 1998

Enhancement of In Situ Bioremediation of BTEX-Contaminated Ground Water by Oxygen Diffusion from Silicone Tubing

Abstract: A field study of oxygen-enhanced biodegradation was carried out in a sandy iron-rich ground water system contaminated with gasoline hydrocarbons. Prior to the oxygen study, intrinsic microbial biodegradation in the contaminant plume had depleted dissolved oxygen and created anaerobic conditions. An oxygen diffusion system made of silicone polymer tubing was installed in an injection well within an oxygen delivery zone containing coarse highly permeable sand. During the study, this system delivered high dissolved oxygen (DO) levels (39 mg/L) to the ground water within a part of the plume. The ground water was sampled at a series of monitors in the test zone downgradient of the delivery well to determine the effect of oxygen on dissolved BTEX, ground water geochemistry, and microbially mediated biodegradation processes. The DO levels and Eh increased markedly at distances up to 2.3 m (7.5 feet) downgradient. Potential biofouling and iron precipitation effects did not clog the well screens or porous medium. The increased dissolved oxygen enhanced the population of aerobes while the activity of anaerobic sulfate-reducing bacteria and methanogens decreased. Based on concentration changes, the estimated total rate of BTEX biodegradation rose from 872 mg/day before enhancement to 2530 mg/day after 60 days of oxygen delivery. Increased oxygen flux to the test area could account for aerobic biodegradation of 1835 mg/day of the BTEX. The estimated rates of anaerobic biodegradation processes decreased based on the flux of sulfate, iron (II), and methane. Two contaminants in the plume, benzene and ethylbenzene, are not biodegraded as readily as toluene or xylenes under anaerobic conditions. Following oxygen enhancement, however, the benzene and ethylbenzene concentrations decreased about 98%, as did toluene and total xylenes.

Rate-Limiting Steps in the Microbial Degradation of Petroleum Hydrocarbons

Abstract: Effective bioremediation of petroleum pollution relies heavily on a fundamental understanding of how microorganisms grow on hydrocarbons. Table 1 outlines the requirements for biodegradation of petroleum hydrocarbons.

Biodegradation of dioxins and furans

Abstract: 1. Aerobic Degradation by Bacteria of Dibenzo-p-Dioxins, Dibenzofurans, Diphenyl Ethers and Their Halogenated Derivatives.- 2. Anaerobic Bacterial Dehalogenation of Polyhalogenated Dioxins and Furans.- 3. Biodegradation of Dioxin and Dioxin-Like Compounds by White-Rot Fungi.- 4. Molecular Genetics of the Degradation of Dioxins by Bacteria.- 5. Biotransformation of Dioxin-Like Compounds by Eukaryotic Cells.- 6. Bioavailability of Dioxin-Like Compounds for Microbial Degradation.- 7. Structure-Biodegradability Relationships for Chlorinated Dibenzo-p-Dioxins and Dibenzofurans.- 8. Biodegradation of Diaryl Ether Pesticides.- Color Figures.

Sorption and microbial degradation of toluenediamines and methylenedianiline in soil under aerobic and anaerobic conditions

Abstract: Three of the major diamines, 2,4-toluenediamine (2,4-TDA), 2,6-toluenediamine (2,6-TDA), and 4,4'-methylenedianiline (4,4'-MDA), used as intermediates in the production of polyurethanes have been studied for their fate in soil. Previous literature has reported variable biodegradation of these industrially important compounds with no information on their expected fate in soil. Their sorption to two soils and biodegradation in soil under both aerobic and anaerobic conditions have been studied. Under aerobic and anaerobic conditions, sorption constants, K oc , for both isomers of TDA on loam soils were 500-1300 after 8 h of contact, and the corresponding K oc values for MDA were 3800-5700 after 8 h of contact. Both isomers of TDA and 4,4'-MDA appear to be sorbed only a little more strongly under aerobic than anaerobic conditions. The 14 carbon-labeled TDA isomers and MDA started to biodegrade immediately after mixing with aerobic soil with the recovery of 2-3% 14 CO 2 after only 3 days. The biodegradation slowed later with recovery of 11-14% 14 CO 2 after 28 days and an apparent 34-40% biodegradation after 1 year, based on loss of 14 C. Under anaerobic methanogenic conditions, no 14 CH 4 or 14 CO 2 was recovered from any of the diamines after 71 days of incubation.

Microbial degradation of high molecular weight polycyclic aromatic hydrocarbons

Abstract: The bacterial degradation of high molecular weight PAHs was investigated by isolating communities and individual strains from a PAH-contaminated site. Microbiological analysis of soils from Port Melbourne, Australia, resulted in the enrichment of five microbial communities capable of degrading pyrene as a sole carbon and energy source. Communities four and five degraded a number of PAH compounds including fluorene, phenanthrene, pyrene and dibenz[a,h]anthracene. Three pure cultures were isolated from community five using a spray plate method with pyrene as the sole carbon source. The cultures were identified as strains of Stenotrophomonas maltophilia on the basis of multiple sequence alignment analysis of 16SrRNA gene sequences. Differentiation of the three strains was possible by pulse field gel electrophoresis and DNA:DNA hybridisation methods. The St. maltophilia strains had similar degradative profiles to community five.

Application of Pneumatic Fracturing to Enhance In Situ Bioremediation

Abstract: A field pilot demonstration integrating pneumatic fracturing and in situ bioremediation was carried out in a gasoline-contaminated, low permeability soil formation. A pneumatic fracturing system was used to enhance subsurface air flow and transport rates, as well as to deliver soil amendments directly to the indigenous microbial populations. An in situ bioremediation zone was established and operated for a period of 50 weeks, which included periodic subsurface injections of phosphate, nitrate, and ammonium salts. Off-gas data indicated the formation of a series of aerobic, denitrifying, and methanogenic microbial degradation zones. Based on soil samples recovered from the site, 79% of soil-phase benzene, toluene, and xylenes (BTX) was removed by the integrated technology. From mass balance calculations, accounting for all physical losses, it was estimated that 85% of the total mass of BTX removed (based on mean concentration levels) was attributable to biodegradation.

Effects of hydrocarbon enrichment on trichloroethylene biodegradation and microbial populations in finished compost

Abstract: This study focused on the capacity of finished compost, often used as packing material in biofiltration units, to support microbial biodegradation of trichloroethylene (TCE). Finished compost was enriched with methane or propane (10% head space) to stimulate cometabolic biodegradation of gaseous TCE. Successful hydrocarbon enrichment, as indicated by rapid depletion of hydrocarbon gas and measurable growth of hydrocarbon-utilizing micro-organisms, occurred within a week. Within batch reactor flasks, approximately 75% of head space TCE (1-40 ppmv) was rapidly sorbed onto compost material. Up to 99% of the remaining head space TCE was removed via biodegradation in compost enriched with either hydrocarbon. Hydrocarbon enrichment with methane or propane corresponded to 10-fold increases in methanotrophic or propanotrophic populations, respectively. Based on growth assessment under different nutritional regimes, there appeared to be complex metabolic interactions within the microbial community in enriched compost. Five separate bacterial cultures were derived from the hydrocarbon-enriched compost and assayed for the ability to degrade TCE.

Computer modelling of microbial hydrolytic dehalogenation

Abstract: The biodegradation of organic compounds by microorganisms is an intrinsically complex process. A large number of sub-processes, like penetration of the compounds to the cells, biochemical catalysis and the release of products are taking place during the biodegradation. The separation of these sub-processes from each other and their detailed study is needed for a better understanding of the basic mechanisms of microbial degradation and for the improvement of bioremediation technologies by means of the construction of a new efficient biocatalyst. This contribution attempts to view the biodegradation reaction - hydrolytic dehalogenation - at the level of catalysing biomolecules. Computer modelling is used to extend the knowledge obtained from X-ray analysis, kinetic measurements and site-directed mutagenesis experiments. Among the issues discussed in this article are the determination of the rate- limiting step of the biodegradation reaction, the identification of the active-site amino acids involved in the reaction mechanism, the prediction of proteins' modifications leading to higher activity and the molecular mechanisms of the adaptation of bacteria for the degradation of xenobiotic compounds.

Intrinsic and enhanced bioremediation in aquifers contaminated with chlorinated and aromatic hydrocarbons in The Netherlands

Abstract: The feasibility of intrinsic and enhanced bioremediation approaches for 16 contaminated sites in the Netherlands are discussed. At at least five out of 10 chlorinated solvent sites, natural attenuation can be used as one of the tools to prevent further dispersion of the plume. At two sites stimulation of the intrinsic dechlorination processes in a bioactived zone is required, and pilot field tests are currently under way. For three sulphatereducing/methanogenic aquifers contaminated with aromatic compounds, microcosm studies demonstrated that natural anaerobic degradation of the risk-determining benzene does not to occur spontaneously. Benzene biodegradation could be initiated by feeding small amounts of oxygen (in all samples) or nitrate (only in one sample), and these techniques are currently tested in field-pilot studies. Redox-microbiological characterisation of two locations contaminated with hexachlorocyclohexanes indicated significant intrinsic biodegradation of HCH's in methanogenic/sulphate-reducing parts of the contaminant plumes, and of the HCH-degradation products chlorophenol and benzene under sulphate/iron reducing conditons. Biostimulated zone's remain required to complete the degradation of HCH and the degradation product monochlorobenzene. Risk-based guideline's for assessing the feasibility of natural attenuation approaches for various contaminant situations are currently under development, making use of already existing protocols (USA) and taking European and National specific conditions, knowledge and regulatory constraints into account.

Microbial enhancement of TCE and 1,2‐DCA solute flux in UF‐membrane bioreactors

Abstract: An ultrafiltration membrane process was used to remove and biograde chlorinated aliphatic hydrocarbons trichloroethylene (TCE) and 1,2-dichloroethane (1,2-DCA) from dilute aqueous streams. The effect of microbial biodegradative activity on TCE and 1,2-DCA solute flux in a polypropylene membrane was examined using microbial strains Pseudomonas cepacia PR131 for the biodegradation of TCE and Xanthobacter autotrophicus GJ10 for the biodegradation of 1,2-DCA. Initial experiments were conducted in diaphragm cells in the absence of microorganisms to determine the diffusion coefficient of 1,2-DCA and TCE in the polypropylene ultrafiltration (UF) membranes. The diffusivities were 4.7 × 10−8 cm2/s for 1,2-DCA and 1.41 × 10−7 cm2/s for TCE. Subsequent experiments were conducted with microorganisms on the permeate side to examine the effect of microbial degradation of 1,2-DCA and TCE on the solute flux across the UF membrane. Experiments were conducted sequentially in batch and flow diaphragm cells and then in a hollow-fiber UF module to systematically examine the effect of microbial activity on the solute flux in each configuration and the ability of mathematical models to predict the microbial enhancement of solute flux. Microbial biodegradation of TCE and 1,2-DCA significantly enhanced the solute flux, and experimental results were correlated with steady- and nonsteady-state solute component balance models for the flow and batch diaphragm cells, respectively. Model and experimental results agree well. Implications for using membrane bioreactors to treat CAH contaminated groundwater and industrial effluents are discussed, as well as a method for examining the effect of biological reaction on membrane transport processes.