Model experiments on the microbial removal of chromium from contaminated groundwater

A bacterial consortium with representatives of sulfate-reducing and denitrifying bacteria was selectively enriched. Model experiments under microaerobic conditions showed that it precipitated chromium from Cr (VI)-containing waters (area of a former electroplating factory, Leipzig, Germany) by two different mechanisms: by sulfate reduction and precipitation as sulfide, and by some direct reduction. Sulfate reduction needed fatty acids as organic substrates and resulted at the first stage in no sulfide accumulation. In the absence of the fatty acids but with straw as organic substrate, the direct reduction of chromium was observed without sulfate reduction. In this case Cr (VI)-reduction rate correlated with that of the denitrification.

Effects of compost and phosphate amendments on arsenic mobility in soils and arsenic uptake by the hyperaccumulator, Pteris vittata L

Chinese brake fern (Pteris vittata L.), an arsenic (As) hyperaccumulator, has shown the potential to remediate As-contaminated soils. This study investigated the effects of soil amendments on the leachability of As from soils and As uptake by Chinese brake fern. The ferns were grown for 12 weeks in a chromated-copper-arsenate (CCA) contaminated soil or in As spiked contaminated (ASC) soil. Soils were treated with phosphate rock, municipal solid waste, or biosolid compost. Phosphate amendments significantly enhanced plant As uptake from the two tested soils with frond As concentrations increasing up to 265% relative to the control. After 12 weeks, plants grown in phosphate-amended soil removed >8% of soil As. Replacement of As by P from the soil binding sites was responsible for the enhanced mobility of As and subsequent increased plant uptake. Compost additions facilitated As uptake from the CCA soil, but decreased As uptake from the ASC soil. Elevated As uptake in the compost-treated CCA soil was related to the increase of soil water-soluble As and As(V) transformation into As(III). Reduced As uptake in the ASC soil may be attributed to As adsorption to the compost. Chinese brake fern took up As mainly from the iron-bound fraction in the CCA soil and from the water-soluble/exchangeable As in the ASC soil. Without ferns for As adsorption, compost and phosphate amendments increased As leaching from the CCA soil, but had decreased leaching with ferns when compared to the control. For the ASC soil, treatments reduced As leaching regardless of fern presence. This study suggest that growing Chinese brake fern in conjunction with phosphate amendments increases the effectiveness of remediating As-contaminated soils, by increasing As uptake and decreasing As leaching.

Microbial reduction of hexavalent chromium under vadose zone conditions

Hexavalent chromium [Cr(VI)] is a common contaminant associated with nuclear reactors and fuel processing. Improper disposal at facilities in and and semiarid regions has contaminated underlying vadose zones and aquifers. The objectives of this study were to assess the potential for immobilizing Cr(VI) using a native microbial community to reduce soluble Cr(VI) to insoluble Cr(III) under conditions similar to those in the vadose zone, and to evaluate the potential for enhancing biological Cr(VI) reduction through nutrient addition. Batch microcosm and unsaturated flow column experiments were performed. Native microbial communities in subsurface sediments with no prior Cr(VI) exposure were shown to be capable of Cr(VI) reduction. In both the batch and column experiments, Cr(VI) reduction and loss from the aqueous phase were enhanced by adding high levels of both nitrate (NO3-) and organic C (molasses). Nutrient amendments resulted in up to 87% reduction of the initial 67 mg L(-1) Cr(VI) in an unsaturated batch experiment. Molasses and nitrate additions to 15 cm long unsaturated flow columns receiving 65 mg L(-1) Cr(VI) resulted in microbially mediated reduction and immobilization of 10% of the Cr during a 45-d experiment. All of the immobilized Cr was in the form of Cr(III), as shown by XANES analysis. This suggests that biostimulation of microbial Cr(VI) reduction in vadose zones by nutrient amendment is a promising strategy, and that immobilization of close to 100% of Cr contamination could be achieved in a thick vadose zone with longer flow paths and longer contact times than in this experiment.

Low-temperature chromium(VI) biotransformation in soil with varying electron acceptors

Effective and low-cost strategies for remediating chromium (Cr)-contaminated soil are needed. Chromium(VI) leaching from contaminated soil into ground water and surface water threatens water supplies and the environment. This study tested indigenous Cr(VI) microbial transformation in batch systems at 10 degrees C in the presence of various electron acceptors. The effects of carbon addition, spiked Cr(VI), and mixing highly contaminated soil with less contaminated soil were investigated. The results indicated that Cr(VI) can be biotransformed in the presence of different electron acceptors including oxygen, nitrate, sulfate, and iron. Sugar addition had the greatest effect on enhancing Cr(VI) removal. Less dissolved organic carbon (DOC) was consumed per amount of Cr(VI) transformed under anaerobic conditions [0.8-93 mg DOC/mg Cr(VI)] compared with aerobic conditions [1.4-265 mg DOC/mg Cr(VI)]. Toxicity of high concentrations (< 160 mg/L) of spiked Cr(VI) were not evident. At Cr(VI) concentrations > 40 mg/L, aerobic conditions promoted faster Cr(VI) reduction than anaerobic conditions with nitrate or sulfate present. Biotransformation of Cr(VI) in highly contaminated soil (22,000 mg Cr/kg) was facilitated by mixing with less-contaminated soil. The study results provide a framework for evaluating indigenous Cr(VI) microbial transformation and enhance the ability to develop strategies for soil treatment.

p53 controls global nucleotide excision repair of low levels of structurally diverse benzo(g)chrysene-DNA adducts in human fibroblasts

Benzo(g)chrysene is a widespread environmental contaminant and potent carcinogen. We have measured the formation and nucleotide excision repair of covalent DNA adducts formed by the DNA-reactive metabolite of this compound in human fibroblasts, in which expression of the p53 tumor suppressor gene could be controlled by a tetracycline-inducible promoter. Cells were exposed for 1 h to 0.01, 0.1, or 1.2 microM (+/-)-anti-benzo(g)chrysene diol-epoxide, and DNA adducts were assessed at various post-treatment times by subjecting isolated DNA to (32)P-postlabeling analysis. Four major DNA adducts were detected, corresponding to the reaction of either the (+)- or (-)-anti-benzo(g)chrysene diol-epoxide stereoisomer with adenine or guanine. Treatment with 1.2 microM resulted in a level of 1100 total adducts/10(8) nucleotides for both p53-proficient and -deficient cells; removal of adducts was not observed in either case. In cells treated with 0.1 microM, the maximum level of total adducts at 24 h was 150/10(8) nucleotides in p53-proficient cells and 210 adducts/10(8) nucleotides in p53-deficient cells. A concentration of 0.01 microM resulted in a maximum of 20 adducts/10(8) nucleotides in p53-proficient cells at 4 h, but 40 adducts/10(8) nucleotides persisted in p53-deficient cells at 24 h. Whereas there were clear differences in the time course of adduct levels in p53-proficient compared with p53-deficient cells treated with 0.1 microM or 0.01 microM, these levels did not decrease extensively over 3 days. This is likely because of the stabilization of the diol-epoxide in cells, and consequent exposure and formation of adducts for many hours after the initial treatment. Furthermore, despite minor quantitative differences, all 4 of the adducts behaved similarly with respect to the effect of p53 expression on their removal. p53 appears to minimize the appearance of benzo(g)chrysene adducts in human cells by up-regulating global nucleotide excision repair and reducing the maximum adduct levels achieved. The fact that this p53-dependent effect is noted at levels of DNA adducts that are commonly found in human tissues (i.e., <100 adducts/10(8) nucleotides) because of environmental factors such as smoking is particularly significant with respect to human carcinogenesis related to environmental exposure.

Comparative tumorigenicity of the environmental pollutant 6-nitrochrysene and its metabolites in the rat mammary gland

Human exposure to the class of nitropolynuclear aromatic hydrocarbons is via inhalation and/or ingestion. Therefore, one of the goals of this study was to determine the propensity of the environmental contaminant 6-nitrochrysene (6-NC) for inducing mammary cancer following its oral administration to female CD rats. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), an established mammary carcinogen in the same animal model, was used as a positive control and trioctanoin as a negative control. Thirty-day-old female CD rats were gavaged once weekly for 8 weeks with 6-NC at 50, 25, or 12.5 micromol/rat or PhIP at 50 micromol/rat in 500 microL of trioctanoin. Twenty-three weeks after the last carcinogen administration, rats were decapitated, necropsied, and evaluated histologically. The most common mammary tumors were adenocarcinomas, followed by adenomas and fibroadenomas. The incidence and multiplicity (mean +/- standard deviation) of mammary adenocarcinomas induced by these two carcinogens at the highest dose (6-NC: 90%, 3.73 +/- 2.74; PhIP: 83%, 2.62 +/- 2.58) were significantly higher than those in control rats (10%, 0.10 +/- 0.31). However, there were no statistically significant differences between groups treated with 6-NC and PhIP or among groups receiving various doses of 6-NC. Following its metabolic activation, 6-NC is known to bind covalently to DNA; however, it remains to be determined whether it can also induce DNA base oxidation. Thus, employing the same route of administration, our studies revealed no effect of 6-NC on the basal level of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the mammary gland in tests at 6, 24, and 48 h after 6-NC treatment and at termination of the carcinogenesis assay in the normal, noninvolved tissue and in mammary tumors. This result suggests that covalent DNA binding of 6-NC metabolites is important in the induction of mammary cancer in rats. Therefore, the other goal of this study was to compare the tumorigenic activities of 6-NC and its metabolites in the rat mammary gland by intramammary administration. This route has also been used in our laboratory to induce mammary cancer in the rat by 6-NC and is employed here to avoid systemic effects and to determine the role of the mammary gland in the metabolic activation of 6-NC and its metabolites. Toward this end, a new method was developed to obtain ample materials of trans-1,2-dihydroxy-1,2-dihydro-6-aminochrysene (1,2-DHD-6-AC); other metabolites were synthesized as reported previously. On the basis of the results, the carcinogenic potency toward the mammary gland is ranked in the following order: 6-NC > 1,2-DHD-6-NC > 6-AC > 6-NCDE > 1,2-DHD-6-AC. Among the metabolites tested, 1,2-DHD-6-NC was the most potent carcinogen. It was significantly more active than its reduced product 1,2-DHD-6-AC. However, the potency of 1,2-DHD-6-NC was not significantly different from 6-AC, a metabolite derived from simple nitroreduction, or from 6-NCDE. Collectively, these results suggest that metabolites derived from both ring-oxidation and nitroreduction contribute to the overall carcinogenicity of 6-NC in the rat mammary gland.

Reduction of Cr(VI) and bioaccumulation of chromium by gram positive and gram negative microorganisms not previously exposed to Cr-stress

Resistance to Cr(VI) is usually associated with its cellular exclusion, precluding enrichment techniques for the isolation of organisms accumulating Cr(VI) via bioreduction to insoluble Cr(III). A technique was developed to screen for potential Cr(VI) reduction in approx. 2000 isolates from a coastal environment, based on the non-specific reduction of selenite and tellurite to Se0 and Te0, and reduction of tetrazolium blue to insoluble blue formazan. The most promising strains were further screened in liquid culture, giving three, which were identified by 16S rRNA sequence analysis as Bacillus pumilus, Exiguobacterium aurantiacum and Pseudomonas synxantha, all of which reduced 100 microM Cr(VI) anaerobically, without growth. The respective removal of Cr(VI) was 90% and 80% by B. pumilus and E. aurantiacum after 48 h and 80% and by P. synxantha after 192 h. With the gram positive strains Cr(VI) promoted loss of flagella and, in the case of B. pumilus, lysis of some cells, but Cr was deposited as an exocellular precipitate which was identified as containing Cr and P using energy dispersive X-ray microanalysis (EDAX). This prompted the testing of Citrobacter sp. N14 (subsequently re-assigned by 16S rRNA sequence analysis and biochemical studies as a strain of Serratia) which bioprecipitates metal cation phosphates via enzymatically-liberated phosphate. This strain reduced Cr(VI) at a rate comparable to that of P. synxantha but Cr(III) was not bioprecipitated where La(III) was removed as LaPO4, even though a similar amount of phosphate was produced in the presence of Cr(III). Since B. pumilus removed most of the Cr(VI), with the formation of cell-bound CrPO4 implicated, this suggests that this strain could have future bioprocess potential.

Synthesis, in vitro metabolism, cell transformation, mutagenicity, and DNA adduction of dibenzo[c,mno]chrysene

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants. Due to its structural similarity with the potent carcinogen dibenzo[a,l]pyrene (DB[a,l]P) and because of its environmental presence, dibenzo[c,mno]chrysene (naphtho[1,2-a]pyrene, N[1,2-a]P) is of considerable research interest. We therefore developed an efficient synthesis of N[1,2-a]P, and examined its in vitro metabolism by male Sprague Dawley rat liver S9 fraction. Its mutagenic activity in S. typhimurium TA 100 and its morphological cell transforming ability in mouse embryo fibroblasts were evaluated. On the basis of spectral analyses, the in vitro major metabolites were identified as the fjord region dihydrodiol trans-9,10-dihydroxy-9,10-dihydro-N[1,2-a]P (N[1,2-a]P-9,10-dihydrodiol), the K-region diols N[1,2-a]P-4,5-dihydrodiol and N[1,2-a]P-7,8-dihydrodiol, and also the 1-, 3-, and 10-hydroxy-N[1,2-a]P; the structure of N[1,2-a]P-9,10-dihydrodiol was also confirmed by independent synthesis. In assays with S. typhimurium TA 100, N[1,2-a]P-9,10-dihydrodiol was half as mutagenic as (+/-)-trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene (B[a]P-7,8-dihydrodiol) at > or =4 nmol/plate. N[1,2-a]P-9,10-dihydrodiol was much more mutagenic than N[1,2-a]P at all dose levels, suggesting that the N[1,2-a]P-9,10-dihydrodiol is the likely proximate mutagen of N[1,2-a]P. Evaluation of morphological cell transformation in C3H10T1/2C18 mouse embryo fibroblasts revealed that N[1,2-a]P was comparable to B[a]P. We further examined the pattern of in vitro adduct formation between calf thymus DNA and (+/-)-anti-9,10-dihydroxy-9,10-dihydro-11,12-epoxy-9,10,11,12-tetrahydro-N[1,2-a]P (N[1,2-a]PDE) and found that dG-adduct formation is 2.9-fold greater than dA-adduct formation. On the basis of our results and those reported in the literature, our working hypothesis is that N[1,2-a]P may be added to the list of potent carcinogens that includes DB[a,l]P. This hypothesis is currently being tested in our laboratory.

Analysis of benzylsuccinates in groundwater by liquid chromatography/tandem mass spectrometry and its use for monitoring in situ BTEX biodegradaton

Benzylsuccinic acid (BS) and methylbenzylsuccinic acid (MeBS) isomers have been proposed as distinctive indicators of anaerobic toluene and xylene metabolism in fuel-contaminated aquifers; however, labor-intensive analytical procedures have limited their analysis at field sites. In this article, a rapid electrospray LC/MS/MS (liquid chromatography/mass spectrometry/mass spectrometry) method for benzylsuccinates is described that involves selected reaction monitoring, internal standard quantification with [ring-2H5]BS, small sample size (<1 mL), and no extraction/concentration steps. The highly selective LC/MS/ MS method was shown to be sensitive (detection limits ca. 0.3 microg/L), accurate, and precise. The method was used to characterize geographic and temporal distributions of BS and MeBS isomers in an anaerobic, hydrocarbon-contaminated aquifer. BS was never detected, and MeBS isomers were detected in the three wells with the highest concentrations of BTEX (benzene, toluene, ethylbenzene, and xylenes); MeBS concentrations ranged from <0.3 to 205 microg/L. A strong linear correlation (r2 = 0.94; n = 12) was found between concentrations of total MeBS isomers and their parent compounds, xylenes, which suggests that anaerobic xylene metabolism at this site was probably first-order rather than zero-order. The novel LC/MS/MS method for BS and MeBS isomers is a promising technique for rapid and reliable monitoring of in situ bioremediation of gasoline-contaminated groundwater.

Biochemical responses of Cr-tolerant and Cr-sensitive mung bean cultivars grown on varying levels of chromium

Biochemical investigations were carried out in Cr-tolerant and Cr-sensitive cultivars of mung bean (Vigna radiata L.) with different concentrations of hexavalent chromium (as K2Cr2O7) in hydroponics culture. Seeds were germinated and grown in the presence or absence of chromium under controlled environmental conditions. Protein, pigment and enzyme analysis were conducted in both Cr-tolerant and Cr-sensitive cultivars of mung bean after 72 h of treatments. Chlorophyll and protein contents were reduced in Cr-sensitive cultivars more than those of the tolerant ones. The enzyme activity varied among the Cr-tolerant and Cr-sensitive ones. Activities of catalase, peroxidase, glucose-6-phosphate dehydrogenase and superoxide dismutase were greater in Cr-sensitive than tolerant cultivars.

Cytochrome P450 1B1, a new keystone in gene-environment interactions related to human head and neck cancer?

Alcohol consumption and tobacco smoking are major causes of head and neck cancers, and regional differences point to the importance of research into gene-environment interactions. Much interest has been focused on polymorphisms of CYP1A1 and of GSTM1 and GSTT1, but a number of studies have not demonstrated significant effects. This has mostly been ascribed to small sample sizes. In general, the impact of polymorphisms of metabolic enzymes appears inconsistent, with some reports of weak-to-moderate associations, and with others of no elevation of risks. The classical cytochrome P450 isoenzyme considered for metabolic activation of polycyclic aromatic hydrocarbons (PAH) is CYP1A1. A new member of the CYP1 family, CYP1B1, was cloned in 1994, currently representing the only member of the CYP1B subfamily. A number of single nucleotide polymorphisms of the CYP1B1 gene have been reported. The amino acid substitutions Val432Leu ( CYP1B1*3) and Asn453Ser ( CYP1B1*4), located in the heme binding domain of CYP1B1, appear as likely candidates to be linked with biological effects. CYP1B1 activates a wide range of PAH, aromatic and heterocyclic amines. Very recently, the CYP1B1 codon 432 polymorphism ( CYP1B1*3) has been identified as a susceptibility factor in smoking-related head-and-neck squamous cell cancer. The impact of this polymorphic variant of CYP1B1 on cancer risk was also reflected by an association with the frequency of somatic mutations of the p53 gene. Combined genotype analysis of CYP1B1 and the glutathione transferases GSTM1 or GSTT1 has pointed to interactive effects. This provides new molecular evidence that tobacco smoke-specific compounds relevant to head and neck carcinogenesis are metabolically activated through CYP1B1 and is consistent with a major pathogenetic relevance of PAH as ingredients of tobacco smoke.

[P450 and carcinogenesis]

Multiple forms of cytochrome P450 play important roles in metabolic activation of a variety of environmental procarcinogens. Large species differences in substrate specificities between experimental animals and humans are critical factors in evaluation of chemical safety. To study the role of human P450s in genotoxic activation of environmental chemicals, transgenic bacteria expressing both human P450s and P450 reductase have been developed for the mutagenicity test. Mice lacking CYP1A2, and CYP1B1, and CYP2E1 were prepared to investigate the mechanism of procarcinogen activation in vivo. The first human transgenic animals were mice carrying human fetus-specific CYP3A7. Using these transgenic mice, mutagenic activation of a natural mycotoxin, aflatoxin B1, catalyzed by CYP3A7 in vivo was demonstrated. This observation was clear in extrahepatic tissues that did not express mouse CYP3A enzymes. In conclusion, P450s are key factors involved in metabolic activation of environmental procarcinogens for their biological actions.

Studies on enhancement of Cr(VI) biosorption by chemically modified biomass of Rhizopus nigricans

This study reports the biosorption of Cr(VI) by chemically modified biomass of Rhizopus nigricans and the possible mechanism of Cr complexation to the adsorbent. The cell wall of this fungus possesses strong complexing property to effectively remove Cr(VI) anions from solution and wastewater. The mechanism of Cr adsorption by R. nigricans was ascertained by chemical modifications of the dead biomass followed by FTIR spectroscopic analysis of the cell wall constituents. Treatment of the biosorbent with mild alkalies (0.01 N NaOH and ammonia solution) and formaldehyde (10%, w/v) deteriorated the biosorption efficiency. However, extraction of the biomass powder in acids (0.1 N HCl and H2SO4), alcohols (50% v/v, CH3OH and C2H5OH) and acetone (50%, v/v) improved the Cr uptake capacity. Reaction of the cell wall amino groups with acetic anhydride reduced the biosorption potential drastically. Blocking of the-COOH groups by treatment with water soluble carbodiimide also resulted in initial lag in Cr binding. Biomass modification experiments conducted using Cetyl Trimethyl Ammonium Bromide (CTAB), Polyethylenimine (PEI), and Amino Propyl Trimethoxy Silane (APTS) improved the biosorption efficiency to exceptionally high levels. The FTIR spectroscopic analysis of the native, Cr bound and the other types of chemically modified biomass indicated the involvement of amino groups of Rhizopus cell wall in Cr binding. The adsorption data of the native and the most effectively modified biomass were evaluated by the Freundlich and the Langmuir adsorption isotherms and the possible adsorption phenomena are also discussed.

The fate of diesel hydrocarbons in soils and their effect on the germination of perennial ryegrass

Hydrocarbon contamination in soils may be toxic to plants and soil microorganisms and act as a source of groundwater contamination. The objective of this study was to evaluate the fate of diesel in soils with or without added nutrients. The soils examined either had or had not a previous history of hydrocarbon contamination. Particular aspects examined were soil respiration, changes in microbial population, breakdown of diesel hydrocarbons, and phytotoxicity to the germination of perennial ryegrass. Soil respiration was measured as evolved CO2. Bacterial population was determined as colony forming units in dilution plates and fungal activity was measured as hyphal length. The fate of individual hydrocarbons was determined by gas chromatography-mass spectrometry after extraction with dichloromethane. When diesel was added to soil with no previous history of hydrocarbon contamination at rates up to 50 mg/g, the respiration response showed a lag phase of 6 days and maximum respiration occurred at day 11. The lag phase was 2 days and maximum respiration occurred at day 3 in soil with a previous history of hydrocarbon contamination. After the peak, respiration decreased up to about 20 days in both soils. Thereafter, respiration become more or less constant but substantially greater than the control. N and P addition along with diesel did not reduce the lag phase but increased the respiration over the first 20 days of incubation. Diesel addition with or without N and P increased the bacterial population 10- to 100-fold but fungal hyphal length did not increase. Diesel addition at a rate of 136 mg/g did not increase the microbial population. Removal of inhibition to germination of perennial ryegrass was linked to the decomposition of nC10 and nC11 hydrocarbons and took from 11 to 30 days at diesel additions up to 50 mg/g depending on the soil. Inhibition to germination of perennial ryegrass persisted to more than 24 weeks at the 136 mg/g of diesel addition.

Effect of microbial activity on the mobility of chromium in soils

The effect of microbial activity on the chemical state of chromium, in a contaminated soil located in the Rhĵne-Alpes region (France), has been investigated. This soil contained 4,700 mg kg(-1) Cr, with about 40% present in the soluble hexavalent form. Indigenous microbial activity was found to significantly reduce Cr(VI) to the less mobile form (III) when the soil was incubated at 30 degrees C in an aqueous medium containing glucose and nutrients. A Cr(VI)-reducing strain of Streptomyces thermocarboxydus was isolated from the contaminated soil. The strain was found to metabolize Cr(VI) in a similar manner as an exogenous inoculum of Pseudomonas fluorescens LB300, and to precipitate chromium as a Cr oxyhydroxide with a gammaCrOOH-like local structure. The Cr(VI)-reducing activity of S. thermocarboxydus was induced, or significantly accelerated, by the aggregation of bacterial cells or their adhesion to suspended solid particles, and was stimulated in pure culture by glycerol and chromate.

Bioremediation of diesel-contaminated soil with composting

The major objective of this research was to find the appropriate mix ratio of organic amendments for enhancing diesel oil degradation during contaminated soil composting. Sewage sludge or compost was added as an amendment for supplementing organic matter for composting of contaminated soil. The ratios of contaminated soil to organic amendments were 1:0.1, 1:0.3, 1:0.5, and 1:1 as wet weight basis. Target contaminant of this research was diesel oil, which was spiked at 10,000 mg/kg sample on a dry weight basis. The degradation of diesel oil was significantly enhanced by the addition of these organic amendments relative to straight soil. Degradation rates of total petroleum hydrocarbons (TPH) and n-alkanes were the greatest at the ratio of 1:0.5 of contaminated soil to organic amendments on wet weight basis. Preferential degradation of n-alkanes over TPH was observed regardless of the kind and the amount of organic amendments. The first order degradation constant of n-alkanes was about twice TPH degradation constant. Normal alkanes could be divided in two groups (C10-C15 versus C16-C20) based on the first order kinetic constant. Volatilization loss of TPH was only about 2% of initial TPH. Normal alkanes lost by volatilization were mainly by the compounds of C10 to C16. High correlations (r=0.80-0.86) were found among TPH degradation rate, amount of CO2 evolved, and dehydrogenase activity.

Fumonisin B1 metabolism by bovine liver microsomes

Only limited and contrasting information is available about the metabolic fate in cattle of fumonisin B1, a mycotoxin produced by moulds of Fusarium. This study was carried out to evaluate the hepatic metabolism of fumonisin B1 by bovine liver microsomes. No biodegradation or metabolization of the mycotoxin by liver microsomes was detectable after incubating fumonisin B1 with bovine microsomes in the presence of a regenerating system for 1 h. No aminopolyol 1, aminopolyol 2 or aminopentol, metabolites of fumonisin B1, were detected in any of the incubated samples. The tolerance of ruminants to fumonisin B1 is apparently not dependent on its detoxification in the rumen.

Pilot plant study of the microbial flora in a diesel fuel contaminated soil

This study focused on the impact of a recent soil pollution of diesel fuel on a site and its indigenous microbial flora. A pilot plant (0.5 m3) was set up and filled with a soil (about 700 kg), artificially and uniformly polluted with diesel fuel (7 g/kg). This plant was then chemically and biologically monitored during the whole experiment (about two years). During the monitoring, a morphological change of the microbial colonies was observed. This was probably due to the acclimation phenomena to the pollution. With batch kinetic studies (10 ml) and increasing the selective pressure of the pollutant, it was possible to select and isolate a microbial consortium and a single strain that developed the ability to use different diesel fuel fractions as carbon sources. GC-MS analytical techniques were used. Results showed that different fractions were degraded at different times. In the batch system, in 7 days, the microbial consortium degraded some aromatic hydrocarbons. The isolate strain, in 20 days, degraded linear hydrocarbons. After a two years acclimation, it was possible to obtain, from a pilot plant, a microbial consortium and a strain able to degrade diesel fuel, for a future bioremediation in situ process.

Evading the proofreading machinery of a replicative DNA polymerase: induction of a mutation by an environmental carcinogen

DNA replication fidelity is dictated by DNA polymerase enzymes and associated proteins. When the template DNA is damaged by a carcinogen, the fidelity of DNA replication is sometimes compromized, allowing mispaired bases to persist and be incorporated into the DNA, resulting in a mutation. A key question in chemical carcinogenesis by metabolically activated polycyclic aromatic hydrocarbons (PAHs) is the nature of the interactions between the carcinogen-damaged DNA and the replicating polymerase protein that permits the mutagenic misincorporation to occur. PAHs are environmental carcinogens that, upon metabolic activation, can react with DNA to form bulky covalently linked combination molecules known as carcinogen-DNA adducts. Benzo[a]pyrene (BP) is a common PAH found in a wide range of material ingested by humans, including cigarette smoke, car exhaust, broiled meats and fish, and as a contaminant in other foods. BP is metabolically activated into several highly reactive intermediates, including the highly tumorigenic (+)-anti-benzo[a]pyrene diol epoxide (BPDE). The primary product of the reaction of (+)-anti-BPDE with DNA, the (+)-trans-anti-benzo[a]pyrene diol epoxide-N(2)-dG ((+)-ta-[BP]G) adduct, is the most mutagenic BP adduct in mammalian systems and primarily causes G-to-T transversion mutations, resulting from the mismatch of adenine with BP-damaged guanine during replication. In order to elucidate the structural characteristics and interactions between the DNA polymerase and carcinogen-damaged DNA that allow a misincorporation opposite a DNA lesion, we have modeled a (+)-ta-[BP]G adduct at a primer-template junction within the replicative phage T7 DNA polymerase containing an incoming dATP, the nucleotide most commonly mismatched with the (+)-ta-[BP]G adduct during replication. A one nanosecond molecular dynamics simulation, using AMBER 5.0, has been carried out, and the resultant trajectory analyzed. The modeling and simulation have revealed that a (+)-ta-[BP]G:A mismatch can be accommodated stably in the active site so that the fidelity mechanisms of the polymerase are evaded and the polymerase accepts the incoming mutagenic base. In this structure, the modified guanine base is in the syn conformation, with the BP moiety positioned in the major groove, without interfering with the normal protein-DNA interactions required for faithful polymerase function. This structure is stabilized by a hydrogen bond between the modified guanine base and dATP partner, hydrophobic interactions between the BP moiety and the polymerase, a hydrogen bond between the modified guanine base and the polymerase, and several hydrogen bonds between the BP moiety and polymerase side-chains. Moreover, the G:A mismatch in this system closely resembles the size and shape of a normal Watson-Crick pair. These features reveal how the polymerase proofreading machinery may be evaded in the presence of a mutagenic carcinogen-damaged DNA, so that a mismatch can be accommodated readily, allowing bypass of the adduct by the replicative T7 DNA polymerase.

Base sequence dependence of in vitro translesional DNA replication past a bulky lesion catalyzed by the exo- Klenow fragment of Pol I

The effects of base sequence, specifically different pyrimidines flanking a bulky DNA adduct, on translesional synthesis in vitro catalyzed by the Klenow fragment of Escherichia coli Pol I (exo(-)) was investigated. The bulky lesion was derived from the binding of a benzo[a]pyrene diol epoxide isomer [(+)-anti-BPDE] to N(2)-guanine (G*). Four different 43-base long oligonucleotide templates were constructed with G* at a site 19 bases from the 5'-end. All bases were identical, except for the pyrimidines, X or Y, flanking G* (sequence context 5'-.XGY., with X, Y = C and/or T). In all cases, the adduct G* slows primer extension beyond G* more than it slows the insertion of a dNTP opposite G* (A and G were predominantly inserted opposite G, with A > G). Depending on X or Y, full lesion bypass differed by factors of approximately 1.5-5 ( approximately 0.6-3.0% bypass efficiencies). A downstream T flanking G on the 5'-side instead of C favors full lesion bypass, while an upstream C flanking G* is more favorable than a T. Various deletion products resulting from misaligned template-primer intermediates are particularly dominant ( approximately 5.0-6.0% efficiencies) with an upstream flanking C, while a 3'-flanking T lowers the levels of deletion products ( approximately 0.5-2.5% efficiencies). The kinetics of (1) single dNTP insertion opposite G* and (2) extension of the primer beyond G* by a single dNTP, or in the presence of all four dNTPs, with different 3'-terminal primer bases (Z) opposite G* were investigated. Unusually efficient primer extension efficiencies beyond the adduct (approaching approximately 90%) was found with Z = T in the case of sequences with 3'-flanking upstream C rather than T. These effects are traced to misaligned slipped frameshift intermediates arising from the pairing of pairs of downstream template base sequences (up to 4-6 bases from G*) with the 3'-terminal primer base and its 5'-flanking base. The latter depend on the base Y and on the base preferentially inserted opposite the adduct. Thus, downstream template sequences as well as the bases flanking G* influence DNA translesion synthesis.

Bioremediation of an area contaminated by a fuel spill

In order to decontaminate a large area of restricted access contaminated by a fuel spill, laboratory and field studies were developed in two steps: (a) monitoring of the laboratory experiment on bacterial growth under aerobic and anaerobic conditions with and without addition of nutrients; and (b) use of the best conditions obtained in (a) for the decontamination of the soil. A hydraulic barrier was installed both to clean the aquifer and to avoid migration of hydrocarbons as a consequence of their solution in the groundwater and subsequent displacement. The objective was to create an ideal environment for the treatment of the affected area that favoured the growth of the indigenous bacteria (Pseudomonas and Arthrobacter) that biodegrade the hydrocarbons. Monitoring of the changes in the total concentration of petroleum hydrocarbons in the soil subjected to bacterial action was performed by gas chromatography. In a field study, the progress of biodegradation of hydrocarbons was evaluated in situ by changes in subsurface CO2/O2 levels by means of an analyser equipped with an infrared detector. Biostimulation and oxygen were the most influential factors for the biodegradation of the hydrocarbons. The use of bioventing of the soil was shown as an excellent technology to promote in situ bioremediation of the polluted area.

Cr (VI) induces cell growth arrest through hydrogen peroxide-mediated reactions

Cr (VI) compounds are widely used in industries and are recognized human carcinogens. The mechanism of carcinogenesis associated with these compounds is not well understood. The present study focused on Cr (VI)-induced cell growth arrest in human lung epithelial A549 cells, using flow cytometric analysis of DNA content. Treatment of the cells with Cr (VI) at 1 microM caused a growth arrest at G2/M phase. An increase in Cr (VI) concentration enhanced the growth arrest. At a concentration of 25 microM, Cr (VI)-induced apoptosis became apparent. Superoxide dismutase (SOD) or sodium formate did not alter the Cr (VI)-induced cell growth arrest. While catalase inhibited growth, indicating H2O2 is an important mediator in Cr (VI)-induced G2/M phase arrest. Electron spin resonance (ESR) spin trapping measurements showed that incubation of cells with Cr (VI) generated hydroxyl radical (*OH). Catalase inhibited the *OH radical generation, indicating that H2O2 was generated from cells stimulated by Cr (VI), and that H2O2 functioned as a precursor for *OH radical generation. The formation of H2O2 from Cr (VI)-stimulated cells was also measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. The mechanism of reactive oxygen species generation involved the reduction of molecular oxygen as shown by oxygen consumption assay. These results support the following conclusions: (a) Reactive oxygen species are generated in Cr (VI)-stimulated A549 cells through reduction of molecular oxygen, (b) Among the reactive oxygen species generated, H2O2 played a major role in causing G2/M phase arrest in human lung epithelial cells.

Prospects for reducing fumonisin contamination of maize through genetic modification

Fumonisins (FB) are mycotoxins found in (italic)Fusarium verticillioides-infected maize grain worldwide. Attention has focused on FBs because of their widespread occurrence, acute toxicity to certain livestock, and their potential carcinogenicity. FBs are present at low levels in most field-grown maize but may spike to high levels depending on both the environment and genetics of the host plant. Among the strategies for reducing risk of FB contamination in maize supplied to the market, development and deployment of Fusarium ear mold-resistant maize germplasm is a high priority. Breeding for increased ear mold tolerance and reduced mycotoxin levels is being practiced today in both commercial and public programs, but the amount of resistance achievable may be limited due to complicated genetics and/or linkage to undesirable agronomic traits. Molecular markers can be employed to speed up the incorporation of chromosomal regions that have a quantitative effect on resistance (quantitative trait loci). Transgenic approaches to ear mold/mycotoxin resistance are now feasible as well. These potentially include genetically enhanced resistance to insect feeding, increased fungal resistance, and detoxification/prevention of mycotoxins in the grain. An example of the first of these approaches is already on the market, namely transgenic maize expressing Bacillus thuringiensis (Bt) toxin, targeted to the European corn borer. Some Bt maize hybrids have the potential to reduce FB levels in field-harvested grain, presumably through reduced feeding of Bt-susceptible insects in ear tissues. However, improved ear mold resistance per se is still an important goal, as the plant will still be vulnerable to noninsect routes of entry to (italic)Fusarium. A second approach, transgene-mediated control of the ability of Fusarium to infect and colonize the ear, could potentially be achieved through overexpression of specific antifungal proteins and metabolites, or enhancement of the plant's own defense systems in kernel tissues. This has not yet been accomplished in maize, although promising results have been obtained recently in other monocots versus other fungal and bacterial pathogens. Achieving reproducible and stable enhanced ear mold resistance under field conditions will be immensely challenging for biotechnologists. A third approach, transgene strategies aimed at preventing mycotoxin biosynthesis, or detoxifying mycotoxins in planta, could provide further protection for the grower in environments where FBs present a risk to the crop even when the maize is relatively resistant to Fusarium mold. In one example of such a strategy, enzymes that degrade FBs have been identified in a filamentous saprophytic fungus isolated from maize, and corresponding genes have been cloned and are currently being tested in transgenic maize.