Showing papers in "Biodegradation in 1995"
TL;DR: It was found that gasoline hydrocarbons could be biodegraded at relatively high rates after appropriate nutrient additions and an unexpected observation was that the optimal concentration of oxygen for the gasoline-degrading microorganisms in these soils was only 10%.
Abstract: Biodegradation was considered to be a feasible approach to remediate petroleum hydrocarbon-contaminated soil from a site at the University of Idaho. Before a full-scale treatment process was designed, the biodegradative capacity of the soil's indigenous microorganisms was tested. Gas chromatography was used to measure gasoline vapor components in the headspace above the contaminated soils held in closed containers. In a study of biodegradation kinetics, gasoline degradation rates under various conditions (different soil cores, temperatures, oxygen concentrations, and nutrient concentrations) were tested. It was found that gasoline hydrocarbons could be biodegraded at relatively high rates after appropriate nutrient additions. An unexpected observation was that the optimal concentration of oxygen for the gasoline-degrading microorganisms in these soils was only 10%.
187 citations
TL;DR: In this paper, the removal of toluene from waste gas was studied in a trickling biofilter, where a high level of water recirculation was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting.
Abstract: The removal of toluene from waste gas was studied in a trickling biofilter. A high level of water recirculation (4.7 m h−1) was maintained in order to keep the liquid phase concentration constant and to achieve a high degree of wetting. For loads in the range from 6 to 150 g m−3 h−1 the maximum volumetric removal rate (elimination capacity) was 35±10 g m−3 h−1, corresponding to a zero order removal rate of 0.11±0.03 g m−2 h−1 per unit of nominal surface area. The surface removal was zero order above the liquid phase concentrations of approximately 1.0 g m−3, corresponding to inlet gas concentrations above 0.7–0.8 g m−3. Below this concentration the surface removal was roughly of first order. The magnitude of the first order surface removal rate constant, k1A
, was estimated to be 0.08–0.27 m h−1 (k1A
a=24–86 h−1). Near-equilibrium conditions existed in the gas effluent, so mass transfer from gas to liquid was obviously relatively fast compared to the biological degradation. An analytical model based on a constant liquid phase concentration through the trickling filter column predicts the effluent gas concentration and the liquid phase concentration for a first and a zero order surface removal. The experimental results were in reasonable agreement with a very simple model valid for conditions with an overall removal governed by the biological degradation and independent of the gas/liquid mass transfer. The overall liquid mass transfer coefficient, KLa, was found to be a factor 6 higher in the system with biofilm compared to the system without. The difference may be explained by: 1. Difference in the wetting of the packing material, 2. Mass transfer occurring directly from the gas phase to the biofilm, and 3. Enlarged contact area between the gas phase and the biofilm due to a rough biofilm surface.
64 citations
Journal Article•
TL;DR: In this paper, a DNA fragment (designated IS1247) was found to encode an open reading frame corresponding to 464 amino acids which showed similarity to putative transposases from two other insertion elements.
Abstract: Monobromoacetate (MBA) is toxic for the 1,2-dichloroethane-degrading bacterium Xanthobacter autotrophicus GJ10 at concentrations higher than 5 mM. Mutants which are able to grow on higher concentrations of MBA were isolated and found to overexpress haloacid dehalogenase, which is encoded by the dhlB gene. In mutant GJ10M50, a DNA fragment (designated IS1247) had copied itself from a position on the chromosome that was not linked to the dhlB region to a site immediately upstream of dhlB, resulting in a 1,672-bp insertion. IS1247 was found to encode an open reading frame corresponding to 464 amino acids which showed similarity to putative transposases from two other insertion elements. In most of the other MBA-resistant mutants of GJ10, IS1247 was also present in one more copy than in the wild type, which had two copies located within 20 kb. After insertion to a site proximal to dhlB, IS1247 was able to transpose itself together with the dhlB gene to a plasmid, without the requirement of a second insertion element being present downstream of dhlB. The results show that IS1247 causes bromoacetate resistance by overexpression and mobilization of the haloacid dehalogenase gene, which mimics steps during the evolution of a catabolic transposon and plasmid during adaptation to a toxic growth substrate.
58 citations
TL;DR: The Gram-negative strain S1, isolated from activated sludge, metabolized 4-chloro-2-methylphenol by an inducible pathway via a modifiedortho-cleavage route as indicated by a transiently secreted intermediate, identified as 2-methyl-4-carboxymethylenebut- 2-en- 4-olide by gas chromatography/mass spectrometry.
Abstract: The Gram-negative strain S1, isolated from activated sludge, metabolized 4-chloro-2-methylphenol by an inducible pathway via a modifiedortho-cleavage route as indicated by a transiently secreted intermediate, identified as 2-methyl-4-carboxymethylenebut-2-en-4-olide by gas chromatography/mass spectrometry. Beside 4-chloro-2-methylphenol only 2,4-dichlorophenol and 4-chlorophenol were totally degraded, without an accumulation of intermediates. The chlorinated phenols tested induced activities of 2,4-dichlorophenol hydroxylase and catechol 1,2-dioxygenase type II. Phenol itself appeared to be degraded more efficiently via a separate, inducibleortho-cleavage pathway. The strain was characterized with respect to its physiological and chemotaxonomic properties. The fatty acid profile, the presence of spermidine as main polyamine, and of ubiquinone Q-10 allowed the allocation of the strain into the α-2 subclass of theProteobacteria. Ochrobactrum anthropi was indicated by fatty acid analysis as the most similar organism, however, differences in a number of physiological features (e.g. absence of nitrate reduction) and pattern of soluble proteins distinguished strain S1 from this species.
52 citations
TL;DR: Results show that both de chlorination activities are co-induced and therefore, that the dechlorination mechanisms may share at least some components, and are considerably faster than previous rates obtained with defined cultures of this organism.
Abstract: Desulfomonile tiedjei, a strict anaerobe capable of reductively dechlorinating 3-chlorobenzoate, also dechlorinates tetrachloroethene and trichloroethene. It is not known, however, if the aryl and aliphatic dechlorination activities are catalyzed by the same enzymatic system. Cultures induced for 3-chlorobenzoate activity dechlorinated tetrachloroethene and trichloroethene to lower chlorinated products while uninduced parallel cultures did not dechlorinate either substrate. The observed rate of PCE dechlorination in induced cultures was 22 mumol h-1 g protein-1, which is considerably faster than previous rates obtained with defined cultures of this organism. These results show that both dechlorination activities are co-induced and therefore, that the dechlorination mechanisms may share at least some components.
51 citations
TL;DR: The inability of biphenyl-degraders to dehalogenate the products of PCB cometabolism is clearly unrelated to metabolism of saturated chloroaliphatic acids, with the notable exception of chloroacetate, since most strains grew on them.
Abstract: As there are at least three types of bacteria involved in the aerobic mineralization of polychlorinated biphenyls (PCBs), this study was undertaken to determine what catabolic features are lacking in biphenyl-degraders and to determine if chlorobenzoate- and chloroacetate-utilizing bacteria are as indigenous to soil as biphenyl-degraders Bacteria were tested for their ability to utilize chlorinated acids and to cometabolize Aroclor 1254 and dibenzo-p-dioxane (dioxin) The broad and variable substrate specificity of the biphenyl dioxygenase among strains was noted by the range of <1 to 53% cometabolism of total PCB congeners and by the oxidation of dioxin, which was not a growth substrate Growth on chloroalkanoic acids was more frequent with 2-chloropropionate (87% of all strains), 3-chloropropionate (72%), 4-chlorobutyrate (66%), and less frequent (28%) withtrans-3-chlorocrotonate However, only one strain,Pseudomonas fluorescens K3, could utilize chloroacetate No biphenyl-utilizers grew on 2- or 4-chlorobenzoate, and only five strains grew on 3-chlorobenzoate Acetate and benzoate-utilizers were found in all three soils tested at levels near 106/g, whereas chloroacetate- or chlorobenzoate-utilizers were not detected The inability of biphenyl-degraders to dehalogenate the products of PCB cometabolism is clearly unrelated to metabolism of saturated chloroaliphatic acids, with the notable exception of chloroacetate, since most strains grew on them Thus, the inability to utilize chloroacetate, a central intermediate in the meta fission pathway, may be relevant to the incomplete catabolism of PCBs by biphenyl-utilizers
49 citations
TL;DR: The mixed microbial population was adapted by varying the growth rate and switching from continuous to batch and back to continuous growth, to degrade these five compounds as well as acrolein, fumaronitrile and maleimide.
Abstract: Effluent from the manufacture of acrylonitrile is difficult to biodegrade. It contains nine major organic components: acetic acid, acrylonitrile, acrylamide, acrylic acid, acrolein, cyanopyridine, fumaronitrile, succinonitrile, and maleimide. A range of bacteria have been isolated that can grow on, or convert all of the organic components of effluent from the manufacture of acrylonitrile. These bacteria can be used as the basis of a mixed culture system to treat the effluent. The bacteria were utilised in batch and continuous cultures to degrade a synthetic wastewater containing acrylonitrile, acrylamide, acrylic acid, cyanopyridine and succinonitrile. The mixed microbial population was adapted by varying the growth rate and switching from continuous to batch and back to continuous growth, to degrade these five compounds as well as acrolein, fumaronitrile and maleimide.
44 citations
TL;DR: A model based on product toxicity provided a reasonable representation of the loss of transformation activity for these compounds.
Abstract: This research investigated the potential for methanotrophic biotransformation of three HCFCs — chlorodifluoromethane (HCFC-22); 1-chloro-1,1-difluoroethane (HCFC-142b); and 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123); and one HFC — 1,2,2,2-tetrafluoroethane (HFC-134a). All of these compounds were biotransformed to differing degrees by methanotrophic mixed culture MM1. Rates of transformation were obtained by monitoring disappearance of the target compounds from the headspace in batch experiments. Henry's constants were determined over a range of conditions to enable estimation of the intrinsic rates of transformation. Intrinsic rates of transformation were obtained by combining a second order rate expression with an expression describing loss of transformation activity due to either endogenous decay or product toxicity. For HCFC-123 and HFC-134a, the independently measured endogenous decay rate for mixed culture MM1 (0.594/day) was sufficient to account for the observed loss of transformation activity with time. However, the endogenous decay rate did not account for the loss of transformation activity for HCFC-22 and HCFC-142b. A model based on product toxicity provided a reasonable representation of the loss of transformation activity for these compounds. The order of reactivity was HCFC-22>HCFC-142b>HFC-134a>HCFC-123, with second order rate coefficients of 0.014, 0.0096, 0.00091, and 0.00054 l/mg-day, respectively. Transformation capacities for HCFC-22 and HCFC-142b were 2.47 and 1.11 µg substrate/mg biomass, respectively.
42 citations
TL;DR: An anaerobic enrichment culture with glucose as the sole source of carbon and energy plus trichloroethene as a potential electron acceptor was inoculated with material from a full size anaerobe charcoal reactor that biologically eliminated dichloromethane from contaminated groundwater, and complete sequential transformation of 10 µM TCE viacis-dichloraethene and chloroetheNE to ethene was reproducibly observed.
Abstract: An anaerobic enrichment culture with glucose as the sole source of carbon and energy plus trichloroethene (TCE) as a potential electron acceptor was inoculated with material from a full size anaerobic charcoal reactor that biologically eliminated dichloromethane from contaminated groundwater (Stromeyer et al. 1991). In subcultures of this enrichment complete sequential transformation of 10 µM TCE viacis-dichloroethene and chloroethene to ethene was reproducibly observed. Maintenance of this activity on subcultivation required the presence of TCE in the medium. The enrichment culture was used to inoculate an anaerobic fixed-bed reactor containing sintered glass Raschig elements as support material. The reactor had a total volume of 1780 ml and was operated at 20 °C in an up-flow mode with a flow rate of 50 ml/h. It was fed continuously with 2 mM glucose and 55 µM TCE. Glucose was converted to acetate as the major product and to a minor amount of methane; TCE was quantitatively dehalogenated to ethene. When, in addition to TCE, tetrachloroethene or 1,2-dichloroethane were added to the system, these compounds were also dehalogenated to ethene. In contrast, 1,1,1-trichloroethane was not dehalogenated, but at 40 µM severely inhibited acetogenesis and methanogenesis. When the concentration of TCE in the feed was raised to 220 µM, chloroethene transiently accumulated, but after an adaptation period ethene was again the only volatile product detected in the effluent. The volumetric degradation rate at this stage amounted to 6.2 µmol/l/h. Since complete transformation of TCE occurred in the first sixth of the reactor volume, the degradation capacity of the system is estimated to exceed this value by factor of about ten.
41 citations
TL;DR: The ammonia oxidation rate by sewage sludge was determined as a function of the dissolved oxygen tension and it was found that a nitrifier concomitantly oxidized ammonia and reduced nitrite to dinitrogen.
Abstract: The ammonia oxidation rate by sewage sludge was determined as a function of the dissolved oxygen tension. Samples of sludge were taken from a domestic waste water treatment pilot plant in which sludge was completely retained by membrane filtration. The samples were subcultured chemolithotrophically in recycling reactors. The gas supplied was a mixture of pure argon and oxygen. The KO2 for ammonia oxidation was estimated to be 0.97 (±0.16) kPa dissolved oxygen. Together with ammonia oxidation and oxygen consumption, dinitrogen gas was produced. So, aerobic denitrification occurred. At dissolved oxygen tensions of 1.25 kPa and higher, the dinitrogen production rate (per N-mole) equalled 20% of the ammonia oxidation rate. This proportion was even 58% at 0.3 kPa dissolved oxygen. At 0.15 kPa dissolved oxygen, however, nitrification hardly proceeded, while dinitrogen production soon stopped. Most likely, a nitrifier concomitantly oxidized ammonia and reduced nitrite to dinitrogen.
39 citations
TL;DR: It is suggested that a dual-substrate model originally formulated to describe no-growth metabolism of one substrate coupled with microbial growth on a second substrate describes linear growth on phenol while nitrogen is available and first-order metabolism of phenol without growth after nitrogen is depleted.
Abstract: In polluted soil or ground water, inorganic nutrients such as nitrogen may be limiting, so that Monod kinetics for carbon limitation may not describe microbial growth and contaminant biodegradation rates. To test this hypothesis we measured14CO2 evolved by a pure culture ofAcinetobacter johnsonii degrading 120 µg14C-phenol per ml in saturated sand with molar carbon:nitrogen (CN) ratios ranging from 1.5 to 560. We fit kinetics models to the data using non-linear least squares regression. Phenol disappearance and population growth were also measured at CN1.5 and CN560.
TL;DR: Enzyme studies using cell-free extracts exhibited dimethylterephthalate esterase and protocatechuate dioxygenase activities and a tentative pathway for the degradation of DMTP has been proposed in A. niger.
Abstract: Aspergillus niger (AG-1) metabolized dimethylterephthalate through monomethylterephthalate, terephthalate and protocatechuate. Degradation of dimethylterephthalate was followed by extraction of residual dimethylterephthalate from the spent medium. The quantitative UV analysis showed that 58% of the dimethylterephthalate supplement was taken up in 144 h. The metabolites were isolated from resting cell cultures. Thin layer chromatography analysis of the extract revealed the presence of two intermediates, monomethylterephthalate and terephthalate. Use of an inhibitor in resting cell culture experiment demonstrated the accumulation of protocatechuate. The time course of protocatechuate accumulation was also studied. Metabolites were identified by employing various physicochemical methods. Enzyme studies using cell-free extracts exhibited dimethylterephthalate esterase and protocatechuate dioxygenase activities. Protocatechuate was oxidized by themeta cleavage pathway. A tentative pathway for the degradation of DMTP has been proposed inA. niger.
TL;DR: As a characteristic product resulting from the cleavage of an aromatic ring, the lactone of 2-hydroxy-4-phenoxymuconic acid was identified and the possible mechanism of ring cleavage to yield this metabolite is discussed.
Abstract: Trichosporon beigelii SBUG 752 was able to transform diphenyl ether. By TLC, HPLC, GC, GC-MS, NMR- and UV-spectroscopy, several oxidation products were identified. The primary attack was initiated by a monooxygenation step, resulting in the formation of 4-hydroxydiphenyl ether, 2-hydroxydiphenyl ether and 3-hydroxydiphenyl ether (48:47:5). Further oxidation led to 3,4-dihydroxydiphenyl ether. As a characteristic product resulting from the cleavage of an aromatic ring, the lactone of 2-hydroxy-4-phenoxymuconic acid was identified. The possible mechanism of ring cleavage to yield this metabolite is discussed.
TL;DR: Dichloromethane dehalogenase, the key enzyme in the utilization of this carbon source, was induced under denitrification conditions to the same specific activity level as under aerobic conditions and cumulatively degraded 35 mM dichlorometrichane within 24 days.
Abstract: Hyphomicrobium sp. strain DM2 was found to grow anaerobically in the presence of nitrate with methanol, formaldehyde, formate or dichloromethane. The estimated growth rate constants with methanol and dichloromethane under denitrification conditions were 0.04 h−1 and 0.015 h−1, respectively, which is twofold and fourfold lower than the rates of aerobic growth with these substrates. Slight accumulation of nitrite was observed in all cultures grown anaerobically with nitrate. Dichloromethane dehalogenase, the key enzyme in the utilization of this carbon source, was induced under denitrification conditions to the same specific activity level as under aerobic conditions. In a fed batch culture under denitrification conditionsHyphomicrobium sp. DM2 cumulatively degraded 35 mM dichloromethane within 24 days. This corresponds to a volumetric degradation rate of 5 mg dichloromethane/l·h and demonstrates that denitrificative degradation offers an attractive possibility for the development of anaerobic treatment systems to remove dichloromethane from contaminated groundwater.
TL;DR: The significance of the two dehalogenase systems in a single bacterial strain is discussed in terms of their contribution to the overall catabolic potential of the organism.
Abstract: Rhodococcus erythropolis Y2 produced two types of dehalogenase: a hydrolytic enzyme, that is an halidohydrolase, which was induced by C3 to C6 1-haloalkane substrates, and at least one oxygenase-type dehalogenase induced by C7 to C16 1-haloalkanes and n-alkanes. The oxygenase-type activity dehalogenated C4 to C18 1-chloroalkanes with an optimum activity towards 1-chlorotetradecane. The halidohydrolase catalysed the dehalogenation of a wide range of 1- and alpha,omega-disubstituted haloalkanes and alpha,omega-substituted haloalcohols. In resting cell suspensions of hexadecane-grown R. erythropolis Y2 the oxygenase-type dehalogenase had a specific activity of 12.9 mU (mg protein)-1 towards 1-chlorotetradecane (3.67 mU mg-1 towards 1-chlorobutane) whereas the halidohydrolase in 1-chlorobutane-grown batch cultures had a specific activity of 44 mU (mg protein)-1 towards 1-chlorobutane. The significance of the two dehalogenase systems in a single bacterial strain is discussed in terms of their contribution to the overall catabolic potential of the organism.
TL;DR: It is proposed that degradation of these more bulky side chain polymers was prevented by the inability of the bacteria to assimilate their monomeric components, which inhibited the successful utilization of secondary carbon sources and thus inhibited colony growth.
Abstract: Utilizing a quantitative clear zone technique, the activity of an extracellular depolymerase system fromPseudomonas maculicola was investigated. Polymer degradation was influenced by the amount and availability of secondary carbon sources, with a simultaneous utilization of both sources. The initial carbon source in the liquid preculture also affected the eventual colony growth and polymer degradation. The enzyme solution was determined to readily degrade poly-3-hydroxyalkanoates (PHAs) with relatively ‘long’ alkyl substituents at the 3 position: poly-3-hydroxyoctanoate (PHO), poly-3-hydroxynonanoate (PHN), and their copolymers (P[HO-co-HN]) and poly-3-hydroxyundecanoate (PHU). However, the system was unable to degrade either PHAs with shorter alkyl groups, including poly-3-hydroxybutyrate (PHB) and the copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P[HB-co-HV]) or PHAs with unusual substituents such as poly(3-hydroxy-5-phenylvaleric acid) (PHPV). It is proposed that degradation of these more bulky side chain polymers was prevented by the inability of the bacteria to assimilate their monomeric components, which inhibited the successful utilization of secondary carbon sources and thus inhibited colony growth.
TL;DR: In this article, Pinus radiata was degraded by the ascomycete Chrysonilia sitophila during 3 months and the total weight loss of the wood was 20% and the carbohydrate and lignin losses were 18% and 25%, respectively.
Abstract: SoftwoodPinus radiata was degraded by the ascomyceteChrysonilia sitophila during 3 months. The total weight loss of the wood was 20% and the carbohydrate and lignin losses were 18% and 25%, respectively. Decayed wood was extracted with solvents of increasing polarity. Methanol and dioxane yielded extracts containing representative low molecular weight degraded lignins. The overall structure of the degraded lignins, as shown by U.V./visible, I.R.,1H and13C NMR spectroscopy, GPC, functional group and elemental analyses, was compared with the structure of milled wood lignin extracted from undecayedP. radiata. The compilation of the data allows us to suggest oxidative Cα-Cβ and β-O-aryl cleavages for the mechanism of lignin degradation by this ascomycete. New saturated carbons on the side chain of the degraded lignins were detected. Based on these data a reductive ability of this microorganism was also suggested.
TL;DR: The actinomyceteRhodococcus chlorophenolicus PCP-1 metabolises pentachlorophenol into ultimate inorganic end products via tetrachloro-p-hydroquinone, which was further dehalogenated in the cytoplasm requiring reductant in the cell free system.
Abstract: The actinomyceteRhodococcus chlorophenolicus PCP-1 metabolises pentachlorophenol into ultimate inorganic end products via tetrachloro-p-hydroquinone. This intermediate was further dehalogenated in the cytoplasm requiring reductant in the cell free system. Tetrafluoro-p-hydroquinone and tetrabromo-p-hydroquinone were also dehalogenated. Chlorophenol analogs, thiol blocking agents and molecular oxygen inhibited the activity. The dehalogenating reactions led to 1,2,4-trihydroxybenzene, which was further metabolized into maleic acid.
TL;DR: The deduced DehRI protein clustered with the NifA nitrogenase regulatory activator family, and was most closely related, with 47.7% similarity, to a ‘NifA-like’ deduced partial sequence from a plasmid-encoded ORF in Pseudomonas sp.
Abstract: The mobile genetic element,DEH found inPseudomonas putida PP3 carries a 2-haloalkanoic acid dehalogenase structural gene,dehI, and its associated regulatory gene,dehRI. The nucleotide sequence ofdehRI was determined. The gene had an open reading frame putatively encoding for a 64 kDa protein containing 571 amino acid residues. The protein was similar to previously published sequences of several other σ54-dependent activator proteins. Amino acid sequence analysis showed that the deduced DehRI protein clustered with the NifA nitrogenase regulatory activator family, and was most closely related, with 47.7% similarity, to a ‘NifA-like’ deduced partial sequence from a plasmid-encoded ORF inPseudomonas sp. strain NS671, associated with L-amino acid production. The domain structure of DehRI was analysed by alignment with other NifA-like and NtrC-like sequences and showed a highly conserved central region of approximately 230 amino acids, and a potential DNA-binding domain. No homology was detected between the deduced DehRI and other σ54-dependent activator sequences at the N-terminus, a result which was consistent with that region being the domain which recognised inducer.
TL;DR: The results suggest that in inoculation to enhance biodegradation, depending on the inoculant, second organic substrate many play an important role in controlling the rate and extent of biodegrading of organic compounds.
Abstract: Many microorganisms fail to degrade pollutants when introduced in different natural environments. This is a problem in selecting inocula for bioremediation of polluted sites. Thus, a study was conducted to determine the success of four inoculants to degradep-nitrophenol (PNP) in lake and industrial wastewater and the effects of organic compounds on the degradation of high and low concentrations of PNP in these environments.Corynebacterium strain Z4 when inoculated into the lake and wastewater samples containing 20 µg/ml of PNP degraded 90% of PNP in one day. Addition of 100 µg/ml of glucose as a second substrate did not enhance the degradation of PNP and the bacterium utilized the two substrates simultaneously. Glucose used at the same concentration (100 µg/ml), inhibited degradation of 20 µg of PNP in wastewater byPseudomonas strain MS. However, glucose increased the extent of degradation of PNP byPseudomonas strain GR. Phenol also enhanced the degradation of PNP in wastewater byPseudomonas strain GR, but had no effect on the degradation of PNP byCorynebacterium strain Z4. Addition of 100 µg/ml of glucose as a second substrate into the lake water samples containing low concentration of PNP (26 ng/ml) enhanced the degradation of PNP and the growth ofCorynebacterium strain Z4. In the presence of glucose, it grew from 2×104 to 4×104 cells/ml in 3 days and degraded 70% of PNP as compared to samples without glucose in which the bacterium declined in cell number from 2×104 to 8×103 cells/ml and degraded only 30% PNP. The results suggest that in inoculation to enhance biodegradation, depending on the inoculant, second organic substrate many play an important role in controlling the rate and extent of biodegradation of organic compounds.
TL;DR: The involved 4-chlorobenzoyl-coenzyme A dehalogenase was purified to apparent homogeneity by a five-step purification procedure and the NH2-terminal amino acid sequence was determined.
Abstract: Pseudomonas sp. CBS3 is capable of growing with 4-chlorobenzoate as sole source of carbon and energy. The removal of the chlorine of 4-chlorobenzoate is performed in the first degradation step by an enzyme system consisting of three proteins. A 4-halobenzoate-coenzyme A ligase activates 4-chlorobenzoate in a coenzyme A, ATP and Mg2+ dependent reaction to 4-chlorobenzoyl-coenzyme A. This thioester intermediate is dehalogenated by the 4-chlorobenzoyl-coenzyme A dehalogenase. Finally coenzyme A is split off by a 4-hydroxybenzoyl-CoA thioesterase to form 4-hydroxybenzoate. The involved 4-chlorobenzoyl-coenzyme A dehalogenase was purified to apparent homogeneity by a five-step purification procedure. The native enzyme had an apparent molecular mass of 120,000 and was composed of four identical polypeptide subunits of 31 kDa. The enzyme displayed an isoelectric point of 6.7. The maximal initial rate of catalysis was achieved at pH 10 at 60 degrees C. The apparent Km value for 4-chlorobenzoyl-coenzyme A was 2.4-2.7 microM. Vmax was 1.1 x 10(-7) M sec-1 (2.2 mumol min-1 mg-1 of protein). The NH2-terminal amino acid sequence was determined. All 4-halobenzoyl-coenzyme A thioesters, except 4-fluorobenzoyl-coenzyme A, were dehalogenated by the 4-chlorobenzoyl-CoA dehalogenase.
TL;DR: Seven strains of fungi were tested individually as well as in different combinations to determine their lignin degrading ability using wheat straw as natural substrate and revealed that in certain combinations the ligninolysis was enhanced to variable extent.
Abstract: Seven strains of fungi were tested individually as well as in different combinations to determine their lignin degrading ability using wheat straw as natural substrate. When tested individuallyPhanerochaete chrysosporium caused a maximum loss in total organic matter (26.45%) as well as in the lignin component (28.93%). The associations between different groups: white-rot plus white-rot, white-rot plus brown-rot and white-rot plus soft-rot fungi revealed that in certain combinations the ligninolysis was enhanced to variable extent.Deadalea flavida plusP. chrysosporium was the best association to bring about a lignin loss of 36.27%.
TL;DR: A kinetic model that describes substrate interactions during reductive dehalogenation reactions is developed and is expanded to include an endogenous electron donor and additional electron acceptor reactions.
Abstract: A kinetic model that describes substrate interactions during reductive dehalogenation reactions is developed. This model describes how the concentrations of primary electron-donor and -acceptor substrates affect the rates of reductive dehalogenation reactions. A basic model, which considers only exogenous electron-donor and -acceptor substrates, illustrates the fundamental interactions that affect reductive dehalogenation reaction kinetics. Because this basic model cannot accurately describe important phenomena, such as reductive dehalogenation that occurs in the absence of exogenous electron donors, it is expanded to include an endogenous electron donor and additional electron acceptor reactions. This general model more accurately reflects the behavior that has been observed for reductive dehalogenation reactions. Under most conditions, primary electron-donor substrates stimulate the reductive dehalogenation rate, while primary electron acceptors reduce the reaction rate. The effects of primary substrates are incorporated into the kinetic parameters for a Monod-like rate expression. The apparent maximum rate of reductive dehalogenation (qm, ap) and the apparent half-saturation concentration (Kap) increase as the electron donor concentration increases. The electron-acceptor concentration does not affect qm, ap, but Kap is directly proportional to its concentration.
TL;DR: The genetic organization of thedhlB region suggested that the expression of dhlC and dhlB was controlled by the product ofdhlR and σ54 which may explain the observed overexpression of the haloalkanoic acid dehalogenase under starvation conditions.
Abstract: The DNA sequence upstream of thedhlB gene encoding the haloalkanoic acid dehalogenase ofXanthobacter autotrophicus GJ10 was determined and contained an open reading frame, designateddhlC, which encoded a protein with a significant similarity with the family of Na+-dependent symport proteins. ThedhlC gene was subcloned under control of a T7 promoter, and found to encode a polypeptide of 45 kDa on SDS-PAGE. Upstream ofdhlC, a −24/−12 promoter sequence was found. Further upstream, in the opposite direction of transcription, another open reading frame, designateddhlR, with homology with the family of σ54-dependent transcriptional activator proteins was detected. ThedhlR gene was cloned and expressed under the control of a T7 promoter and encoded a polypeptide of 51 kDa on SDS-PAGE. The genetic organization of thedhlB region suggested that the expression ofdhlC anddhlB was controlled by the product ofdhlR and σ54 which may explain the observed overexpression of the haloalkanoic acid dehalogenase under starvation conditions.
TL;DR: The inoculum originated from a mixture of sludges from sewage treatment plants with alternating nitrification and denitrification and was able to degrade toluene under anaerobic conditions in the presence of nitrate, nitrite, nitric oxide, or nitrous oxide.
Abstract: Batch experiments were carried out to investigate the stoichiometry and kinetics of microbial degradation of toluene under denitrifying conditions. The inoculum originated from a mixture of sludges from sewage treatment plants with alternating nitrification and denitrification. The culture was able to degrade toluene under anaerobic conditions in the presence of nitrate, nitrite, nitric oxide, or nitrous oxide. No degradation occurred in the absence of Noxides. The culture was also able to use oxygen, but ferric iron could not be used as an electron acceptor. In experiments with14C-labeled toluene, 34%±8% of the carbon was incorporated into the biomass, while 53%±10% was recovered as14CO2, and 6%±2% remained in the medium as nonvolatile water soluble products. The average consumption of nitrate in experiments, where all the reduced nitrate was recovered as nitrite, was 1.3±0.2 mg of nitrate-N per mg of toluene. This nitrate reduction accounted for 70% of the electrons donated during the oxidation of toluene. When nitrate was reduced to nitrogen gas, the consumption was 0.7±0.2 mg per mg of toluene, accounting for 97% of the donated electrons. Since the ammonia concentration decreased during degradation, dissimilatory reduction of nitrate to ammonia was not the reductive process. The degradation of toluene was modelled by classical Monod kinetics. The maximum specific rate of degradation, k, was estimated to be 0.71 mg toluene per mg of protein per hour, and the Monod saturation constant, K s , to be 0.2 mg toluene/l. The maximum specific growth rate, μ max , was estimated to be 0.1 per hour, and the yield coefficient, Y, was 0.14 mg protein per mg toluene.
TL;DR: In this article, the authors investigated the anaerobic transformation of xylene in a laboratory biofilm system with nitrate as an electron acceptor, and found that the presence of toluene was necessary for stimulation of o-xylene transformation.
Abstract: The purpose of this work was to investigate the anaerobic transformation ofo-xylene in a laboratory biofilm system with nitrate as an electron acceptor.o-Xylene was degraded cometabolically with toluene as primary carbon source. A mass balance showed thato-xylene was not mineralized but transformed.o-Methyl-benzalcohol ando-methyl-benzaldehyde were identified as intermediates ofo-xylene transformation which resulted in the formation ofo-methyl-benzoic acid as an end product. A cross inhibition phenomenon was observed between toluene ando-xylene. The presence of toluene was necessary for stimulation ofo-xylene transformation, but above a toluene concentration of 1–3 mg/L theo-xylene removal rate dramatically decreased. In returno-xylene inhibited the toluene degradation at concentrations above 2–3 mg/L.
TL;DR: The degradation pathway for dinoseb (2-sec-butyl-4,6-dinitrophenol) under reducing conditions was investigated and intermediates may exist as quinones or hydroquinones, depending on the pH and redox potential in the culture.
Abstract: The degradation pathway for dinoseb (2-sec-butyl-4,6-dinitrophenol) under reducing conditions was investigated. Cultures were inoculated with a dinoseb-degrading anaerobic enrichment culture used in field studies. Biotransformation intermediates were extracted with ethyl acetate and analyzed by high pressure liquid chromatography, gas chromatography, and mass spectrometry. Dinoseb degradation involves reduction of the nitro groups to amino groups followed by replacement with hydroxyl groups. Depending on the pH and redox potential in the culture, these intermediates may exist as quinones or hydroquinones.
TL;DR: A highly enriched denitrifying mixed culture transformedo-xylene cometabolically along with toluene by methyl group oxidation by attributed to a mechanism linked to the initial oxidation of the methyl group.
Abstract: A highly enriched denitrifying mixed culture transformed o-xylene co-metabolically along with toluene by methyl group oxidation. o-Methyl benzaldehyde and o-methyl benzoic acid accumulated transiently as metabolic products of o-xylene transformation. Transformation of o-methyl benzyl alcohol and o-methyl benzaldehyde occurred independently of toluene degradation and resulted in the formation of a compound coeluting with o-methyl benzoic acid on a gas chromatograph. The co-metabolic relationship between toluene and o-xylene could be attributed to a mechanism linked to the initial oxidation of the methyl group.
TL;DR: There were however no significant changes in the chlorinated dioxin components during this treatment, and mid-exponential phaseFlavobacterium sp.
Abstract: The reduction of pentachlorophenol in treated timber, after inoculation with pentachlorophenol-degrading bacterial species,Rhodococcus chlorophenolicus andFlavobacterium sp., and the white-rot fungusPhanerochaete chrysosporium, was monitored in solid substrate systems and in liquid culture suspensions. In solid substrate systems there was no significant pentachlorophenol degradation by the bacterial species under a variety of conditions. Under similar conditions,Phanerochaete chrysosporium transformed over 80% of the starting concentration of 500 ppm to pentachloroanisole. In liquid culture suspensions however, mid-exponential phaseFlavobacterium sp. cells were able to degrade over 99% of the pentachlorophenol in sawdust and wood chips due to the extraction of PCP from the timber as a water soluble salt. There were however no significant changes in the chlorinated dioxin components during this treatment.
TL;DR: The results indicate that in environments with low oxygen concentrations and alternative, more easily degradable, substrates the degradation rates of chloroaromatic compounds by aerobic organisms may be negatively affected.
Abstract: From long-term chemostat experiments, variants ofPseudomonas aeruginosa JB2 were obtained which exhibited altered properties with respect to the metabolism of 2,5-dichlorobenzoic acid (2,5-DBA). Thus, unlike the original strain JB2-WT, strain JB2-var1 is able to grow in continuous culture on 2,5-DBA as the sole limiting carbon and energy source. Yet, at a dilution rate of 0.07 h−1 and a dissolved oxygen concentration of ≤ 12 µM, even with this strain no steady states with 2,5-DBA alone could be established in continuous cultures. Yet another strain was obtained after prolonged continuous growth of JB2-var1 in the chemostat. It has improved 2,5-DBA degrading capabilities which become apparent only during growth in continuous culture: a lower apparent K m for 2,5-DBA and lowered steady-state residual concentrations of 2,5 DBA. Although with this strain steady states were obtained at oxygen concentrations as low as 11 µM, at further lowered concentrations this was no longer possible. In C-limited continuous cultures of JB2-var1 or JB2-var2, addition of benzoic acid (BA) to the feed reduced the amounts of 2,5-DBA degraded, which was most apparent at low oxygen concentrations (< 30 µM). At higher dissolved oxygen concentrations the addition of BA resulted in increasing cell-densities but did not affect the residual steady state concentration of 2,5-DBA. Indeed, whole cell suspensions from chemostat cultures grown on BA plus 2,5-DBA did show a lower apparent affinity for 2,5-DBA than those from cultures grown on 2,5-DBA alone. These results indicate that in environments with low oxygen concentrations and alternative, more easily degradable, substrates the degradation rates of chloroaromatic compounds by aerobic organisms may be negatively affected.