Abstract  Skeletal muscle weakness is a reported ailment in individuals working in commercial hog confinement facilities. To date, specific mechanisms responsible for this symptom remain undefined. The purpose of this study was to assess whether hog barn dust (HBD) contains components that are capable of binding to and modulating the activity of type 1 ryanodine receptor Ca2+-release channel (RyR1), a key regulator of skeletal muscle function. HBD collected from confinement facilities in Nebraska were extracted with chloroform, filtered, and rotary evaporated to dryness. Residues were resuspended in hexane-chloroform (20:1) and precipitates, referred to as HBDorg, were air-dried and studied further. In competition assays, HBDorg dose-dependently displaced [3H]ryanodine from binding sites on RyR1 with an IC50 of 1.5±0.1 microg/ml (Ki=0.4±0.0 microg/ml). In single-channel assays using RyR1 reconstituted into a lipid bilayer, HBDorg exhibited three distinct dose-dependent effects: first it increased the open probability of RyR1 by increasing its gating frequency and dwell time in the open state, then it induced a state of reduced conductance (55% of maximum) that was more likely to occur and persist at positive holding potentials, and finally it irreversibly closed RyR1. In differentiated C2C12 myotubes, addition of HBD triggered a rise in intracellular Ca2+ that was blocked by pretreatment with ryanodine. Since persistent activation and/or closure of RyR1 results in skeletal muscle weakness, these new data suggest that HBD is responsible, at least in part, for the muscle ailment reported by hog confinement workers.

Abstract  BACKGROUND/AIM: We undertook a case-control and a case-case study to examine the possible association of p53 codon72 polymorphism with the breast cancer risk and resistance to anthracycline-based chemotherapy.

PATIENTS AND METHODS: Case-control study: This study enrolled 175 patients with breast cancer treated at the Salah Aziez Institute and 159 healthy Tunisian women (matched for age, ethnicity and origin), used as a control, with no clinical evidence of any neoplastic disorder. Case-Case study: 400 breast cancer patients, with invasive ductal carcinoma (IDC) treated with anthracycline based-chemotherapy. Genomic DNA was isolated from whole-blood leucocytes using the phenol-chloroform method. Anthracycline response was scored according to the World Health Organization (WHO) criteria. P53 codon72 polymorphism was genotyped using real-time polymerase chain reaction (RT-PCR) with the TaqMan method. Data were statistically analyzed using the Chi-square test.

RESULTS: Clinical data revealed that among the 400 patients, one quarter was resistant to chemotherapy treatment. Genetic data revealed that the p53 Arg72Pro genotype was found to be greatly associated with breast cancer risk (p<0.001), as well as tumor site (p=0.046). However, resistance to anthracycline-based chemotherapy does not seem to be correlated with p53 codon72 polymorphism in our population. Also, the distribution of tumor size, lymph node involvement and tumor grade was not significantly different among the polymorphic variants.

CONCLUSION: We conclude that p53 codon72 polymorphism is involved in susceptibility to developing breast cancer. It may be a factor of progression when breast sites are taken into account. However, there is no evidence indicating that Arg72Pro SNP may influence response to anthracycline-based chemotherapy.

Abstract  BACKGROUND: Knowledge on HPV prevalence and genotype distribution in HSIL and ICC is highly essential for the introduction of an effective vaccination program and appropriate epidemiological monitoring of viral ecology before and after vaccination in Congo. This study aimed to determine the specific-HPV genotypes in HSIL and ICC among women in southwestern Congo.

METHODS: 125 archival paraffin-embedded biopsy collected between 2008 and 2012 and histologically diagnosed were investigated. DNA extraction was performed using the phenol/chloroform method. HPV search was performed by nested-PCR using MY09/MY11 and GP5+/GP6+ consensus primers followed by direct sequencing.

RESULTS: The mean age of participants was 44.3 ± 8.2 years. Overall, HPV prevalence was 89.6% (112/125) with all high-risk genotypes. HPV-DNA was detected in 81.5% (53/65) of HSIL and 98.3% (59/60) of ICC. HPV 16 the most common genotype was detected in 47.1% (25/53) of HSIL and 52.5% (31/59) of ICC. Other types identified were: HPV 33 (22.6%), HPV 18 (15%), HPV 31 (11.3%) and HPV 69 (3.7%) in HSIL, and HPV 33 (28.8%), HPV 18 (11.8%), HPV 31 (5%) and HPV 35 (1.7%) in ICC. Knowing that the ADC accounted for 6.7% (4/60) of ICC cases, HPV 18 was identified in 25% (1/4) of these cases against 75% (3/4) for HPV 16.

CONCLUSION: Our study showed that HPV 16, 33, 18 and 31 were the four most common genotypes in women with HSIL and ICC. These findings indicate that current vaccines against HPV could help to reduce the burden of cervical cancer in Congo.

Abstract  DNA isolation is a crucial step of conducting genetic studies in any organism. However, this process is quite difficult when studying fungi because of the need to damage the fungal cell walls of specific structures. In this study, we developed a method for the rapid and efficient isolation of fungal DNA based on simultaneous mechanical and enzymatic cell wall degradation. There are several typical modifications of the standard phenol-chloroform DNA extraction method. This method can be modified to degrade the fungal cell wall. The first step of the presented DNA extraction included manual homogenization in modified lysis buffer. Next, enzymatic digestion using 2 enzymes was conducted, including lyticase and proteinase K. To carefully select the most favorable conditions, we developed an economical, rapid, and reliable method for fungal DNA extraction that ensures both high efficiency and proper purity, which are essential for further analyses.

Abstract  The presence of abundant storage proteins in plant embryos greatly impedes seed proteomics analysis. Vicilin (or globulin-1) is the most abundant storage protein in maize embryo. There is a need to deplete the vicilins from maize embryo extracts for enhanced proteomics analysis. We here reported a chloroform-assisted phenol extraction (CAPE) method for vicilin depletion. By CAPE, maize embryo proteins were first extracted in an aqueous buffer, denatured by chloroform and then subjected to phenol extraction. We found that CAPE can effectively deplete the vicilins from maize embryo extract, allowing the detection of low-abundance proteins that were masked by vicilins in 2-DE gel. The novelty of CAPE is that it selectively depletes abundant storage proteins from embryo extracts of both monocot (maize) and dicot (soybean and pea) seeds, whereas other embryo proteins were not depleted. CAPE can significantly improve proteome profiling of embryos and extends the application of chloroform and phenol extraction in plant proteomics. In addition, the rationale behind CAPE depletion of abundant storage proteins was explored.

Abstract  Although the enzymes for dissimilatory sulfate reduction by microbes have been studied, the mechanisms for transcriptional regulation of the encoding genes remain unknown. In a number of bacteria the transcriptional regulator Rex has been shown to play a key role as a repressor of genes producing proteins involved in energy conversion. In the model sulfate-reducing microbe Desulfovibrio vulgaris Hildenborough, the gene DVU_0916 was observed to resemble other known Rex proteins. Therefore, the DVU_0916 protein has been predicted to be a transcriptional repressor of genes encoding proteins that function in the process of sulfate reduction in D. vulgaris Hildenborough. Examination of the deduced DVU_0916 protein identified two domains, one a winged helix DNA-binding domain common for transcription factors, and the other a Rossman fold that could potentially interact with pyridine nucleotides. A deletion of the putative rex gene was made in D. vulgaris Hildenborough, and transcript expression studies of sat, encoding sulfate adenylyl transferase, showed increased levels in the D. vulgaris Hildenborough Rex (Rex(DvH)) mutant relative to the parental strain. The Rex(DvH)-binding site upstream of sat was identified, confirming RexDvH to be a repressor of sat. We established in vitro that the presence of elevated NADH disrupted the interaction between Rex(DvH) and DNA. Examination of the 5' transcriptional start site for the sat mRNA revealed two unique start sites, one for respiring cells that correlated with the Rex(DvH)-binding site and a second for fermenting cells. Collectively, these data support the role of RexDvH as a transcription repressor for sat that senses the redox status of the cell.

Abstract  The adsorption characteristics of chloroform, acetone, and acetonitrile on commercial activated carbon (C1), two types of activated carbon fibers (F1 and F2), and sludge adsorbent (S1) was investigated. The chloroform influent concentration ranged from 90 to 7800 ppm and the acetone concentration from 80 to 6900 ppm; the sequence of the adsorption capacity of chloroform and acetone on adsorbents was F2>F1 approximately C1 approximately S1. The adsorption capacity of acetonitrile ranged from 4 to 100 mg/g, corresponding to the influent range from 43 to 2700 ppm for C1, S1, and F1. The acetonitrile adsorption capacity of F2 was approximately 20% higher than that of the other adsorbents at temperatures<30 degrees C. The Freundlich equation fit the data better than the Langmuir and Dubinin-Radushkevich (D-R) equations. The adsorption rate of carbon fibers is higher than that of the other adsorbents due to their smaller fiber diameter and higher surface area. The micropore diffusion coefficient of VOC on activated carbon and sludge adsorbent was approximately 10(-4) cm2 s(-1). The diffusion coefficient of VOC on carbon fibers ranged from 10(-8) to 10(-7) cm2 s(-1). The small carbon fiber pore size corresponds to a smaller diffusion coefficient.

Abstract  The aim of this study was the preparation of microparticles containing rifampicin using a biodegradable polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) for oral administration produced by a bacteria. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microparticles with and without rifampicin were prepared by the emulsification and solvent evaporation method, in which chloroform and polyvinyl alcohol are used as the solvent and emulsifier, respectively. Microparticles were obtained within a size range of 20-60 microm by changing the initial poly(3-hydroxybutyrate-co-3-hydroxyvalerate), polyvinyl alcohol and rifampicin concentrations. An encapsulation efficiency value of 14% was obtained. The optimized total yield of 60% of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/ rifampicin was obtained. A load of 0.035 mg/1 mg of PHBV was reached. Almost 90% of the drug loaded in the microparticles was released after 24 h. The size, encapsulation efficiency and ribampicin release of the microparticles varied as a function of the initial poly(3-hydroxybutyrate-co-3-hydroxyvalerate), polyvinyl alcohol and rifampicin concentrations. It was demonstrated that the microencapsulated rifampicin, although was not totally available in the medium, exhibited a similar inhibition value as free rifampicin at 24 h of incubation with S. aureus. Cytotoxicity assays demonstrated a reduction of the toxicity when rifampicin was microencapsulated in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) while maintaining its antibacterial activity.

Abstract  An improved pulse sequence for SLF experiments based on the magic sandwich (MS) scheme for homo-nuclear dipolar decoupling is proposed. The sequence incorporates a double MS, both on I and S spins and has been named as EXE-MS2. The proposed scheme which has a scaling factor of 1 is observed to be free from low intensity artifacts and provides better line-widths particularly for S spins labeled at multiple sites. The pulse sequence which has been applied on static oriented samples incorporates the EXE scheme where direct polarization of the S spin in the B(0) field is utilized in the place of polarization inversion and is observed to perform well without any loss of sensitivity while ensuring considerable reduction in rf power input into the sample. The EXE scheme has also been tested for solid samples under MAS.

Abstract  A H(2)-based, denitrifying and sulfate-reducing membrane biofilm reactor (MBfR) was effective for removing 1,1,1-trichloroethane (TCA) and chloroform (CF) by reductive dechlorination. When either TCA or CF was first added to the MBfR, reductive dechlorination took place immediately and then increased over 3 weeks, suggesting enrichment for TCA- or CF-dechlorinating bacteria. Increasing the H(2) pressure increased the dechlorination rates of TCA or CF, and it also increased the rate of sulfate reduction. Increased sulfate loading allowed more sulfate reduction, and this competed with reductive dechlorination, particularly the second steps. The acceptor flux normalized by effluent concentration can be an efficient indicator to gauge the intrinsic kinetics of the MBfR biofilms for the different reduction reactions. The analysis of normalized rates showed that the kinetics for reductive-dechlorination reactions were slowed by reduced H(2) bio-availability caused by a low H(2) pressure or competition from sulfate reduction.

Abstract  INTRODUCTION: Effective removal of gutta-percha in endodontic retreatment is a significant factor to ensure a favorable outcome from failed procedures. The purpose of this study was to evaluate the efficacy of a nickel-titanium rotary instrument system with or without a solvent versus stainless steel hand files for gutta-percha removal.

METHODS: Forty extracted human maxillary anterior teeth were prepared and filled. They were divided into 4 groups: Gates-Glidden and K-files, Gates-Glidden and K-files with chloroform, ProTaper Universal rotary retreatment system, and ProTaper Universal rotary retreatment system with chloroform. The operating time was recorded. The teeth were longitudinally sectioned and photographed. The images were analyzed and the filling remnants were quantified by using the IMAGE TOOL software.

RESULTS: With Kruskall-Wallis test, statistical analysis showed that there was no significant difference between the techniques in regard to the amount of the endodontic filling remnants (P < .05); however, the ProTaper Universal rotary retreatment system was faster than the hand files (P < .05).

CONCLUSIONS: All of the techniques proved helpful for the removal of endodontic filling material, and they were similar in material remaining after retreatment, but the ProTaper Universal rotary retreatment system without chloroform was faster.

Abstract  A method for quality screening is suggested to detect volatile impurities in inorganic coagulants that are used for drinking water treatment. Static headspace gas chromatography with mass spectrometry detection (HS-GCMS) is sensitive and selective to detect volatiles in low concentrations. This study has discovered that volatile organic impurities are detectable in ferric and aluminium-based coagulants which are used for drinking water treatment. For ferric chloride, 2-propanol was detected at a level of 17-24 microg ml(-1), acetone at 0.7-1.7 microg ml(-1), 1,1,1-trichloroacetone at 0.02-0.04 microg ml(-1), trichloromethane at 0.01-0.02 microg ml(-1) and toluene at 0.01-0.12 microg ml(-1). For ferric chloride sulfate, acetone was detected at a level of 0.12 microg ml(-1), 1,1,1-trichloroacetone at 0.06-0.08 microg ml(-1), trichloromethane at 0.13-0.23 microg ml(-1), bromodichloromethane at 0.04-0.06 microg ml(-1) and dibromochloromethane at 0.04-0.05 microg ml(-1). For aluminium hydroxide chloride, only trichloromethane was detectable, but below the method detection limits (MDL). Although the concentrations of these impurities in commercial coagulants are low, this observation is important and should have impact on water industries for them to pay attention to the chemicals they are using for drinking water production.

Abstract  Sonochemistry is a technique that offers promise for pollutant degradation, but earlier studies on various chlorinated substrates do not give a definitive view of the effectiveness of this methodology. We now report a thorough study of ultrasonic operational variables upon perchloroethylene (PCE) degradation in water (variables include ultrasonic frequency, power and system geometry as well as substrate concentration) and we attempt to close the mass balance where feasible. We obtained fractional conversions of >97% showing very effective loss of pollutant starting material, and give mechanistic proposals for the reaction pathway based on cavitational phenomena inducing pyrolytic and free radical processes. We note major products of Cl(-) and CO(2)/CO, and also trichloroethylene (TCE) and dichloroethylene (DCE) at ppm concentrations as reported earlier. The formation at very low (ppb) concentration of small halocompounds (CHCl(3), CCl(4)) and also of higher-mass species, such as pentachloropropene, hexachloroethane, is noteworthy. But of particular importance in our work is the discovery of significant quantities of chloroacetate derivatives at ppm concentrations. Although these compounds have been described as by-products with other techniques such as radiolysis or photochemistry, this is the first time that these products have been identified in the sonochemical treatment of PCE; this allows a much more effective account of the mass balance and may explain earlier inconsistencies. This reaction system is now better identified, but a corollary is that, because these haloacetates are themselves species of some toxicity, the use of ultrasound here may not sufficiently diminish wastewater toxicity. Copyright © 2010 Elsevier B.V. All rights reserved.

Abstract  The hydroxyl radical (OH) is a key oxidant involved in the removal of air pollutants and greenhouse gases from the atmosphere. The ratio of Northern Hemispheric to Southern Hemispheric (NH/SH) OH concentration is important for our understanding of emission estimates of atmospheric species such as nitrogen oxides and methane. It remains poorly constrained, however, with a range of estimates from 0.85 to 1.4 (refs 4, 7-10). Here we determine the NH/SH ratio of OH with the help of methyl chloroform data (a proxy for OH concentrations) and an atmospheric transport model that accurately describes interhemispheric transport and modelled emissions. We find that for the years 2004-2011 the model predicts an annual mean NH-SH gradient of methyl chloroform that is a tight linear function of the modelled NH/SH ratio in annual mean OH. We estimate a NH/SH OH ratio of 0.97 ± 0.12 during this time period by optimizing global total emissions and mean OH abundance to fit methyl chloroform data from two surface-measurement networks and aircraft campaigns. Our findings suggest that top-down emission estimates of reactive species such as nitrogen oxides in key emitting countries in the NH that are based on a NH/SH OH ratio larger than 1 may be overestimated.

Abstract  BACKGROUND: Anisomeles malabarica R. Br. (Lamiaceae) is extensively used in traditional medicine in major parts of India for several medicinal purposes, including their use in rheumatism.

MATERIALS AND METHODS: The air-dried leaves of A. malabarica were extracted with ethanol, defatted with n-hexane and then successively partitioned into chloroform and n-butanol fractions. Bioassay-guided fractionation and purification of chloroform fraction from A. malabarica lead to the isolation of lipoxygenase (LOX) inhibitors. The structures of isolated compounds were elucidated by ultraviolet, infrared, (1)H nuclear magnetic resonance (NMR), (13)C NMR and mass spectrometry spectroscopic techniques and assessed further by in vitro soybean lipoxygenase (sLOX) assay. In addition, the enzyme type inhibition was evaluated through molecular docking technique as a part of computational study.

RESULTS: The bioactive compounds 3, 4 dihydroxy benzoic acid (1) and 4', 5, 7-trihydroxyflavone (2) were isolated from chloroform fraction of A. malabarica, whose bioactivity was observed to be dose-dependent compared to n-butanol fraction. Among the compounds, 3, 4 dihydroxy benzoic acid showed significant sLOX inhibitory activity with 74.04% ±2.6% followed by 4', 5, 7-trihydroxyflavone (34.68% ±1.9%). The computational analysis of compounds showed their molecular interaction with important amino acid residues and nonheme iron atom in the catalytic site of LOX by enlightening their potential binding mode at molecular level.

CONCLUSIONS: The LOX inhibitory constituents were identified from A. malabarica by means of bioassay-guided fractionation process. The results derived from in vitro and computational experiments confirm the potential of the isolated compounds and provide additional evidence for its traditional use in inflammatory disorders.

Abstract  The task of fitting dose-response models to experimental data can be performed using a spreadsheet with a built-in optimization engine. This paper shows how the task of point and interval estimation can be performed using Microsoft EXCEL. A case study is presented on the carcinogenic dose-response behavior of chloroform.

Abstract  A wide variety of chemicals, both naturally occurring and synthetic, have exhibited carcinogenic activity in rodent liver. Some are clearly DNA reactive whereas others produce only epigenetic effects. Hepatocarcinogens are categorized according to these properties and the characteristics of examples of both types are reviewed. DNA-reactive rodent hepatocarcinogens represent human cancer risks even at non-toxic exposures, whereas epigenetic agents pose either no risk because their effects are specific to rodents, or a risk only at high exposures at which they produce the same cellular effects in humans that are the basis for their carcinogenic activity in rodents.

Abstract  Estimates of dermal dose from exposures to toxic chemicals are typically derived using models that assume instantaneous establishment of steady-state dermal mass flux. However, dermal absorption theory indicates that this assumption is invalid for short-term exposures to volatile organic chemicals (VOCs). A generalized distributed parameter physiologically-based pharmacokinetic model (DP-PBPK), which describes unsteady state dermal mass flux via a partial differential equation (Fickian diffusion), has been developed for inhalation and dermal absorption of VOCs. In the present study, the DP-PBPK model has been parameterized for chloroform, and compared with two simpler PBPK models of chloroform. The latter are lumped parameter models, employing ordinary differential equations, that do not account for the dermal absorption time lag associated with the accumulation of permeant chemical in tissue represented by permeability coefficients. All three models were evaluated by comparing simulated post-exposure exhaled breath concentration profiles with measured concentrations following environmental chloroform exposures. The DP-PBPK model predicted a time-lag in the exhaled breath concentration profile, consistent with the experimental data. The DP-PBPK model also predicted significant volatilization of chloroform, for a simulated dermal exposure scenario. The end-exposure dermal dose predicted by the DP-PBPK model is similar to that predicted by the EPA recommended method for short-term exposures, and is significantly greater than the end-exposure dose predicted by the lumped parameter models. However, the net dermal dose predicted by the DP-PBPK model is substantially less than that predicted by the EPA method, due to the post-exposure volatilization predicted by the DP-PBPK model. Moreover, the net dermal dose of chloroform predicted by all three models was nearly the same, even though the lumped parameter models did not predict substantial volatilization.

Abstract  It is now well-recognized that human environmental exposures are not to single chemicals. Rather, humans are exposed, either concurrently or sequentially, to multiple chemicals. Challenges that chemical mixtures pose for risk assessment and toxicology are presented. Challenge areas include increasing the peer-reviewed publication of human studies, improving access to peer-reviewed data and examining multiple target organs. Two difficult challenges are development of a common, consistent language and the use of appropriate and innovative experimental designs and analyses. The challenge of elucidation of mechanism(s) offers a rational basis for extrapolation across dose levels, exposure durations and exposure routes as well as to other species and to other similar chemicals. Of particular importance is focusing effort on those areas of investigation where answers have the greatest potential for reducing uncertainty in risk assessments for chemical mixtures and on those chemical mixtures and multiple chemical exposures that have the greatest potential impact on human health. A particularly fruitful area for future investigation is determination of the likelihood of nonadditive interactions in humans exposed to multiple chemicals at environmental exposure levels.

Abstract  In 1969, the International Agency for Research on Cancer (IARC) initiated the Monographs Programme to evaluate the carcinogenic risk of chemicals to humans. Results from short-term mutagenicity tests were first included in the IARC Monographs in the mid-1970s based on the observation that most carcinogens are also mutagens, although not all mutagens are carcinogens. Experimental evidence at that time showed a strong correlation between mutagenicity and carcinogenicity and indicated that short-term mutagenicity tests are useful for predicting carcinogenicity. Although the strength of these correlations has diminished over the past 20 years with the identification of putative nongenotoxic carcinogens, such tests provide vital information for identifying potential human carcinogens and understanding mechanisms of carcinogenesis. The short-term test results for agents compiled in the EPA/IARC Genetic Activity Profile (GAP) database over nearly 15 years are summarized and reviewed here with regard to their IARC carcinogenicity classifications. The evidence of mutagenicity or nonmutagenicity based on a 'defining set' of test results from three genetic endpoints (gene mutation, chromosomal aberrations, and aneuploidy) is examined. Recommendations are made for assessing chemicals based on the strength of evidence from short-term tests, and the implications of this approach in identifying mutational mechanisms of carcinogenesis are discussed. The role of short-term test data in influencing the overall classification of specific compounds in recent Monograph volumes is discussed, particularly with reference to studies in human populations. Ethylene oxide is cited as an example. Copyright 1999 Elsevier Science B.V.

Abstract  #We investigated N cycling and denitrification rates following five years of N and dolomite amendments to whole-tree harvested forest plots at the long-term soil productivity experiment in the Fernow Experimental Forest in West Virginia, USA. We hypothesized that changes in soil chemistry and nutrient cycling induced by N fertilization would increase denitrification rates and the N2O:N2 ratio. Soils from the fertilized plots had a lower pH (2.96) than control plots (3.22) and plots that received fertilizer and dolomite (3.41). There were no significant differences in soil %C or %N between treatments. Chloroform-labile microbial biomass carbon was lower in fertilized plots compared to control plots, though this trend was not significant. Extractable soil NO3- was elevated in fertilized plots on each sample date. Soil-extractable NH4+, NO3-, pH, microbial biomass carbon, and %C varied significantly by sample date suggesting important seasonal patterns in soil chemistry and N cycling. In particular, the steep decline in extractable NH4+ during the growing season is consistent with the high N demands of a regenerating forest. Net N mineralization and nitrification also varied by date but were not affected by the fertilization and dolomite treatments. In a laboratory experiment, denitrification was stimulated by NO3- additions in soils collected from all field plots, but this effect was stronger in soils from the unfertilized control plots, suggesting that chronic N fertilization has partially alleviated a NO3- limitation on denitrification rates. Dextrose stimulated denitrification only in the whole-tree-harvest soils. Denitrification enzyme activity varied by sample date and was elevated in fertilized plots for soil collected in July 2000 and June 2001. There were no detectable treatment effects on N2O or N2 flux from soils under anaerobic conditions, though there was strong temporal variation. These results suggest that whole-tree harvesting has altered the N status of these soils so they are less prone to N saturation than more mature forests. It is likely that N losses associated with the initial harvest and high N demand by aggrading vegetation is minimizing, at least temporarily, the amount of inorganic N available for nitrification and denitrification, even in the fertilized plots in this experiment.

Abstract  Sulfate-reducing bacteria (SRB) in anoxic waters and sediments are the major producers of methylmercury in aquatic systems. Although a considerable amount of work has addressed the environmental factors that control methylmercury formation and the conditions that control bioavailability of inorganic mercury to SRB, little work has been undertaken analyzing the biochemical mechanism of methylmercury production. The acetyl-coenzyme A (CoA) pathway has been implicated as being key to mercury methylation in one SRB strain, Desulfovibrio desulfuricans LS, but this result has not been extended to other SRB species. To probe whether the acetyl-CoA pathway is the controlling biochemical process for methylmercury production in SRB, five incomplete-oxidizing SRB strains and two Desulfobacter strains that do not use the acetyl-CoA pathway for major carbon metabolism were assayed for methylmercury formation and acetyl-CoA pathway enzyme activities. Three of the SRB strains were also incubated with chloroform to inhibit the acetyl-CoA pathway. So far, all species that have been found to have acetyl-CoA activity are complete oxidizers that require the acetyl-CoA pathway for basic metabolism, as well as methylate mercury. Chloroform inhibits Hg methylation in these species either by blocking the methylating enzyme or by indirect effects on metabolism and growth. However, we have identified four incomplete-oxidizing strains that clearly do not utilize the acetyl-CoA pathway either for metabolism or mercury methylation (as confirmed by the absence of chloroform inhibition). Hg methylation is thus independent of the acetyl-CoA pathway and may not require vitamin B12 in some and perhaps many incomplete-oxidizing SRB strains.

Abstract  Sulfate-reducing bacteria (SRB) in anoxic waters and sediments are the major producers of methylmercury in aquatic systems. Although a considerable amount of work has addressed the environmental factors that control methylmercury formation and the conditions that control bioavailability of inorganic mercury to SRB, little work has been undertaken analyzing the biochemical mechanism of methylmercury production. The acetyl-coenzyme A (CoA) pathway has been implicated as being key to mercury methylation in one SRB strain, Desulfovibrio desulfuricans LS, but this result has not been extended to other SRB species. To probe whether the acetyl-CoA pathway is the controlling biochemical process for methylmercury production in SRB, five incomplete- oxidizing SRB strains and two Desulfobacter strains that do not use the acetyl-CoA pathway for major carbon metabolism were assayed for methylmercury formation and acetyl-CoA pathway enzyme activities. Three of the SRB strains were also incubated with chloroform to inhibit the acetyl-CoA pathway. So far, all species that have been found to have acetyl-CoA activity are complete oxidizers that require the acetyl-CoA pathway for basic metabolism, as well as methylate mercury. Chloroform inhibits Hg methylation in these species either by blocking the methylating enzyme or by indirect effects on metabolism and growth. However, we have identified four incomplete-oxidizing strains that clearly do not utilize the acetyl-CoA pathway either for metabolism or mercury methylation (as confirmed by the absence of chloroform inhibition). Hg methylation is thus independent of the acetyl-CoA pathway and may not require vitamin B12 in some and perhaps many incomplete-oxidizing SRB strains.