Enhanced dimethyl phthalate biodegradation by accelerating phthalic acid di-oxygenation

The aerobic biodegradation of dimethyl phthalate (DMP) is initiated with two hydrolysis reactions that generate an intermediate, phthalic acid (PA), that is further biodegraded through a two-step di-oxygenation reaction. DMP biodegradation is inhibited when PA accumulates, but DMP’s biodegradation can be enhanced by adding an exogenous electron donor. We evaluated the effect of adding succinate, acetate, or formate as an exogenous electron donor. PA removal rates were increased by 15 and 30% for initial PA concentrations of 0.3 and 0.6 mM when 0.15 and 0.30 mM succinate, respectively, were added as exogenous electron donor. The same electron-equivalent additions of acetate and formate had the same acceleration impacts on PA removal. Consequently, the DMP-removal rate, even PA coexisting with DMP simultaneously, was accelerated by 37% by simultaneous addition of 0.3 mM succinate. Thus, lowering the accumulation of PA by addition of an electron increased the rate of DMP biodegradation.     

Influence of bioturbation on denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in freshwater sediments

Intensive agriculture leads to increased nitrogen fluxes (mostly as nitrate, NO₃ ^?) to aquatic ecosystems, which in turn creates ecological problems, including eutrophication and associated harmful algal blooms. These problems have focused scientific attention on understanding the controls on nitrate reduction processes such as denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Our objective was to determine the effects of nutrient-tolerant bioturbating invertebrates (tubificid oligochaetes) on nitrogen cycling processes, specifically coupled nitrification–denitrification, net denitrification, DNRA, and biogeochemical fluxes (O₂, NO₃ ^?, NH₄ ⁺, CO₂, N₂O, and CH₄) in freshwater sediments. A mesocosm experiment determined how tubificid density and increasing NO₃ ^? concentrations (using N¹⁵ isotope tracing) interact to affect N cycling processes. At the lowest NO₃ ^? concentration and in the absence of bioturbation, the relative importance of denitrification to DNRA was similar (i.e., 49.6 and 50.4 ± 8.1 %, respectively). Increasing NO₃ ^? concentrations in the control cores (without fauna) stimulated denitrification, but did not enhance DNRA, which significantly altered the relative importance of denitrification compared to DNRA (94.6 vs. 5.4 ± 0.9 %, respectively). The presence of tubificid oligochaetes enhanced O₂, NO₃ ^?, NH₄ ⁺ fluxes, greenhouse gas production, and N cycling processes. The relative importance of denitrification to DNRA shifted towards favoring denitrification with both the increase in NO₃ ^? concentrations and the increase of bioturbation activity. Our study highlights that understanding the interactions between nutrient-tolerant bioturbating species and nitrate contamination is important for determining the nitrogen removal capacity of eutrophic freshwater ecosystems.     

Hydrogen-Dependent Nitrogenase Activity and ATP Formation in Rhizobium japonicum Bacteroids

Rhizobium japonicum 122 DES bacteroids from soybean nodules possess an active H₂-oxidizing system that recycles all of the H₂ lost through nitrogenase-dependent H₂ evolution. The addition of 72 μM H₂ to suspensions of bacteroids increased O₂ uptake 300% and the rate of C₂H₂ reduction 300 to 500%. The optimal partial pressure of O₂ was increased, and the partial pressure of O₂ range for C₂H₂ reduction was extended by adding H₂. A supply of succinate to bacteroids resulted in effects similar to those obtained by adding H₂. Both H₂ and succinate provided respiratory protection for the N₂-fixing system in bacteroids. The oxidation of H₂ by bacteroids increased the steady-state pool of ATP by 20 to 40%. In the presence of 50 mM iodoacetate, which caused much greater inhibition of endogenous respiration than of H₂ oxidation, the addition of H₂ increased the steady-state pool of ATP in bacteroids by 500%. Inhibitor evidence and an absolute requirement for O₂ indicated that the H₂-stimulated ATP synthesis occurred through oxidative phosphorylation. In the presence of 50 mM iodoacetate, H₂-dependent ATP synthesis occurred at a rate sufficient to support nitrogenase activity. The addition of H₂ to H₂ uptake-negative strains of R. japonicum had no effect on ATP formation or C₂H₂ reduction. It is concluded that the H₂-oxidizing system in H₂ uptake-positive bacteroids benefits the N₂-fixing process by providing respiratory protection of the O₂-labile nitrogenase proteins and generating ATP to support maximal rates of C₂H₂ reduction by oxidation of the H₂ produced from the nitrogenase system.     

Enhanced Sono-Fenton-Like Oxidation of PAH-Contaminated Soil Using Nano-Sized Magnetite as Catalyst: Optimization with Response Surface Methodology

In the current study, Fe₃O₄ NPs were synthesized and used as catalysts in a sono-Fenton-like process for remediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soil. The effects of operational variables were studied using central composite design (CCD) optimization approach. Results indicated that the effects of H₂O₂ concentration, Fe₃O₄ NPs dosage, ultrasonic power and pH were significant for pyrene removal as a contaminant model. In optimum experimental conditions, including H₂O₂ concentration of 78 mM, Fe₃O₄ NPs dosage of 18 mM, ultrasonic power of 313 W and pH value of 3.46, the observed pyrene removal was obtained 98.37%, which was verified through the additional experimental tests (99.33%). Pseudo first-order kinetic model was well fitted with the experimental data of pyrene removal with significant coefficient of correlation (R²: 0.9672). Accordingly, an unwashed real soil sample containing diffident PAHs (pyrene, flurene, acenaphthylene, phenenthrene, chrysene, etc) was subjected to sono-Fenton-like process based on optimized conditions. The obtained findings revealed that the removal (%) ranged between 37.7% and 85.19% for different PAHs.     

Effects of macrophyte-associated nitrogen cycling bacteria on denitrification in the sediments of the eutrophic Gonghu Bay, Taihu Lake

Integrated Elodea nuttallii-immobilized nitrogen cycling bacteria (INCB) technology was used for ecological restoration in the eutrophic Gonghu Bay, Taihu Lake. Sediment denitrification was investigated through microcosm incubations with four different treatments: bare sediment core as control without restoration, sediment + E. nuttallii, sediment + E. nuttallii + INCB, and sediment + INCB. The sediments with E. nuttallii-INCB assemblage (E-INCB) had the highest denitrification rates among all the treatments, and the E-INCB increased the denitrification rate by 162% in the sediments. The presence of macrophytes yielded a penetration depth of O₂ to more than 20 mm below the sediment–water interface (SWI), while the depth was only 4 mm in the sediments without macrophytes. The quantity of denitrifier in E-INCB sediments (within ~2 cm below the SWI) showed a significant increasing trend during one-month incubation, which was one order of magnitudes higher than that in the sediments without INCB. Macrophytes caused deeper O₂ penetration and increased oxic-anoxic interface, which could stimulate the coupled nitrification–denitrification. The high denitrification rate of the E-INCB treatment may result from the increased inorganic nitrogen content in the vicinity of the SWI, causing more nitrate to reach the anoxic denitrification zone. The results showed that E-INCB assemblage could increase benthic N removal by stimulating denitrification via combined O₂ penetration and enhanced microbial N cycling processes. E-INCB might be used as a potential restoration method for controlling fresh water system eutrophication.     

Anoxic oxidation of arsenite linked to chemolithotrophic denitrification in continuous bioreactors

In this study, the anoxic oxidation of arsenite (As(III)) linked to chemolithotrophic denitrification was shown to be feasible in continuous bioreactors. Biological oxidation of As(III) was stable over prolonged periods of operation ranging up to 3 years in continuous denitrifying bioreactors with granular biofilms. As(III) was removed with a high conversion efficiency (>92%) to arsenate (As(V)) in periods with high volumetric loadings (e.g., 3.5–5.1 mmol As L day^?1). The maximum specific activity of sampled granular sludge from the bioreactors was 0.98 ± 0.04 mmol As(V) formed g^?1 VSS day^?1 when determined at an initial concentration of 0.5 mM As(III). The microbial population adapted to high influent concentrations of As(III) up to 5.2 mM. However, the As(III) oxidation process was severely inhibited when 7.6–8.1 mM As(III) was fed. Activity was restored upon lowering the As(III) concentration to 3.8 mM. Several experimental strategies were utilized to demonstrate a dependence of the nitrate removal on As(III) oxidation as well as a dependence of the As(III) removal on nitrate reduction. The molar stoichiometric ratio of As(V) formed to nitrate removed (corrected for endogenous denitrification) in the bioreactors approximated 2.5, indicating complete denitrification was occurring. As(III) oxidation was also shown to be linked to the complete denitrification of NO to N₂ gas by demonstrating a significantly enhanced production of N₂ beyond the background endogenous production in a batch bioassay spiked with 3.5 mM As(III). The N₂ production also corresponded closely to the expected stoichiometry of 2.5 mol As(III) mol^?1 N₂–N for complete denitrification. Biotechnol. Bioeng. 2010;105: 909–917. © 2009 Wiley Periodicals, Inc.     

Nitrification and denitrification in a midwestern stream containing high nitrate: in situ assessment using tracers in dome-shaped incubation chambers

The extent to which in-stream processes alter or remove nutrient loads in agriculturally impacted streams is critically important to watershed function and the delivery of those loads to coastal waters. In this study, patch-scale rates of in-stream benthic processes were determined using large volume, open-bottom benthic incubation chambers in a nitrate-rich, first to third order stream draining an area dominated by tile-drained row-crop fields. The chambers were fitted with sampling/mixing ports, a volume compensation bladder, and porewater samplers. Incubations were conducted with added tracers (NaBr and either ¹⁵N[NO₃ ^?], ¹⁵N[NO₂ ^?], or ¹⁵N[NH₄ ⁺]) for 24–44 h intervals and reaction rates were determined from changes in concentrations and isotopic compositions of nitrate, nitrite, ammonium and nitrogen gas. Overall, nitrate loss rates (220–3,560 μmol N m^?2 h^?1) greatly exceeded corresponding denitrification rates (34–212 μmol N m^?2 h^?1) and both of these rates were correlated with nitrate concentrations (90–1,330 μM), which could be readily manipulated with addition experiments. Chamber estimates closely matched whole-stream rates of denitrification and nitrate loss using ¹⁵N. Chamber incubations with acetylene indicated that coupled nitrification/denitrification was not a major source of N₂ production at ambient nitrate concentrations (175 μM), but acetylene was not effective for assessing denitrification at higher nitrate concentrations (1,330 μM). Ammonium uptake rates greatly exceeded nitrification rates, which were relatively low even with added ammonium (3.5 μmol N m^?2 h^?1), though incubations with nitrite demonstrated that oxidation to nitrate exceeded reduction to nitrogen gas in the surface sediments by fivefold to tenfold. The chamber results confirmed earlier studies that denitrification was a substantial nitrate sink in this stream, but they also indicated that dissolved inorganic nitrogen (DIN) turnover rates greatly exceeded the rates of permanent nitrogen removal via denitrification.     

The control of mitochondrial succinate-dependent H<Subscript>2</Subscript>O<Subscript>2</Subscript> production

In brain mitochondria succinate activates H₂O₂ release, concentration dependently (starting at 15 μM), and in the presence of NAD dependent substrates (glutamate, pyruvate, β-hydroxybutyrate). We report that TCA cycle metabolites (citrate, isocitrate, α-ketoglutarate, fumarate, malate) individually and quickly inhibit H₂O₂ release. When they are present together at physiological concentration (0.2, 0.01, 0.15, 0.12, 0.2 mM respectively) they decrease H₂O₂ production by over 60% at 0.1–0.2 mM succinate. The degree of inhibition depends on the concentration of each metabolite. Acetoacetate is a strong inhibitor of H₂O₂ release, starting at 10 μM and acting quickly. It potentiates the inhibition induced by TCA cycle metabolites. The action of acetoacetate is partially removed by β-hydroxybutyrate. Removal is minimal at 0.1 mM acetoacetate, and is higher at 0.5 mM acetoacetate. We conclude that several inhibitors of H₂O₂ release act jointly and concentration dependently to rapidly set the required level of H₂O₂ generation at each succinate concentration.     

Influence of hydrological connectivity of riverine wetlands on nitrogen removal via denitrification

Wetland ecosystems in agricultural areas often become progressively more isolated from main water bodies. Stagnation favors the accumulation of organic matter as the supply of electron acceptors with water renewal is limited. In this context it is expected that nitrogen recycling prevails over nitrogen dissipation. To test this hypothesis, denitrification rates, fluxes of dissolved oxygen (SOD), inorganic carbon (DIC) and nitrogen and sediment features were measured in winter and summer 2007 on 22 shallow riverine wetlands in the Po River Plain (Northern Italy). Fluxes were determined from incubations of intact cores by measurement of concentration changes or isotope pairing in the case of denitrification. Sampled sites were eutrophic to hypertrophic; 10 were connected and 12 were isolated from the adjacent rivers, resulting in large differences in nitrate concentrations in the water column (from <5 to 1,133 μM). Benthic metabolism and denitrification rates were investigated by two overarching factors: season and hydrological connectivity. SOD and DIC fluxes resulted in respiratory quotients greater than one at most sampling sites. Sediment respiration was coupled to both ammonium efflux, which increased from winter to summer, and nitrate consumption, with higher rates in river-connected wetlands. Denitrification rates measured in river-connected wetlands (35–1,888 μmol N m^?2 h^?1) were up to two orders of magnitude higher than rates measured in isolated wetlands (2–231 μmol N m^?2 h^?1), suggesting a strong regulation of the process by nitrate availability. These rates were also significantly higher in summer (9–1,888 μmol N m^?2 h^?1) than in winter (2–365 μmol N m^?2 h^?1). Denitrification supported by water column nitrate (D_W) accounted for 60–100% of total denitrification (Dtot); denitrification coupled to nitrification (D_N) was probably controlled by limited oxygen availability within sediments. Denitrification efficiency, calculated as the ratio between N removal via denitrification and N regeneration, and the relative role of denitrification for organic matter oxidation, were high in connected wetlands but not in isolated sites. This study confirms the importance of restoring hydraulic connectivity of riverine wetlands for the maintenance of important biogeochemical functions such as nitrogen removal via denitrification.     

Enhancement of the Bioremediation of Pyrene-Contaminated Soils Using a Hematite Nanoparticle-based Modified Fenton Oxidation in a Sequenced Approach

The effect of modified Fenton oxidation using synthesized hematite nanoparticles and sodium pyrophosphate as a chelating agent was investigated for the pretreatment of pyrene-contaminated soil in a sequence with bioremediation. Synthesized hematite nanoparticles comprised hematite according to X-ray diffraction (XRD) analysis, with particle sizes ranging between 28 and 55 nm. Three pyrene-degrading bacteria, Bacillus cereus, Acidovorax wohlfahrtii, and Bacillus thuringiensis, were isolated from hydrocarbon-contaminated soil and used as inoculums for the bioremediation. A sequence of modified Fenton oxidation-bioremediation using a synthesized hematite nanoparticles dosage of 30 mM and H₂O₂ concentration of 300 mM significantly enhanced the pyrene removal rate to 96%, 87%, and 82% compared to 88%, 59%, and 37%, which were obtained during the bioremediation alone for synthetically fresh, aged, and naturally contaminated soil with initial pH 7, respectively. The results of kinetic studies indicated that modified Fenton oxidation of pyrene-contaminated soil was best fitted with a pseudo-first order kinetic model. Consequently, a sequence of modified Fenton-bioremediation can effectively remediate polycyclic aromatic hydrocarbon-contaminated sites in a shorter reaction time than bioremediation alone.     

Study the biocatalyzing effect and mechanism of cellulose acetate immobilized redox mediators technology (CE-RM) on nitrite denitrification

The biocatalyzing effect of a novel cellulose acetate immobilized redox mediators technology (CE-RM) on nitrite denitrification process was studied with anthraquinone, 1,8-dichloroanthraquinone, 1,5-dichloroanthraquinone and 1,4,5,8-tetrachloroanthraquinone. The results showed that the immobilized 1,4,5,8-tetrachloroanthraquinone presented the best biocatalyzed effect which increased nitrite denitrification rate to 2.3-fold with 12 mmol/L 1,4,5,8-tetrachloroanthraquinone. The unequal biocatalyzing effect was due to the quantity and position of –Cl substituent in anthraquinone-structure. Moreover, the nitrite denitrification rate was increased with the oxidation reduction potential (ORP) values becoming more negative during the biocatalyzing process. The stabilized ORP value with 12 mmol/L immobilized 1,4,5,8-tetrachloroanthraquinone were 81 mV lower than the control. At the same time, the more OH^? was produced with the higher nitrite removal rate achieved in the nitrite denitrification process. In addition, a positive linear correlation was found between the nitrite removal reaction constants k [gNO₂ ^?–N/(gVSS d)] and immobilized 1,4,5,8-tetrachloroanthraquinone concentration (C _{1,4,5,8-tetrachloroanthraquinone}), which was k = 1.8443 C _{1,4,5,8-tetrachloroanthraquinone} + 33.75(R ² = 0.9411). The initial nitrite concentration of 179 mgNO₂ ^?–N/L resulted in the maximum nitrite removal rate, which was 6.526[gNO₂ ^?–N/(gVSS d)]. These results show that the application of cellulose acetate immobilized redox mediators (CE-RM) can be valuable for increasing nitrite denitrification rate.     

NaCl-induced heme oxygenase in roots of rice seedlings is mediated through hydrogen peroxide

Recent findings have suggested that H₂O₂ is an important signaling molecule for regulating plant responses to abiotic stress. H₂O₂ plays a critical role in NaCl stress. Heme oxygenase (HO) is known to play a protective role against oxidative stress. In this study, we examined the possible involvement of H₂O₂ in regulating NaCl-promoted HO activity in rice roots. Treatment with NaCl increased HO activity and H₂O₂ content in rice roots. As well, NaCl could induce OsHO1 mRNA expression. NaCl (150 mM) and NaNO₃ (150 mM) were equally effective in inducing HO activity. However, mannitol at the concentration (276 mM) iso-osmotic with 150 mM NaCl had no effect on HO activity. NaCl-promoted HO activity and OsHO1 expression in rice roots was reduced by NADPH oxidase inhibitors i.e. dipehnyleneiodonium and imidazole. Moreover, exogenous application of H₂O₂ enhanced the activity of HO and the mRNA level of OsHO1. Our data suggest that H₂O₂ production plays a positive role in NaCl- induced HO activity by enhancing its mRNA level in rice roots.     

外源H_2S对NO_3~-胁迫下番茄幼苗生理生化特性的影响

采用营养液水培方法,通过外源施加H2S供体NaHS(100μmol/L),研究了信号分子H2S对100mmol/L NO3-胁迫下番茄幼苗生理生化特性的影响。结果表明:(1)NO3-胁迫下,随着处理时间的延长,番茄幼苗的株高、根长、鲜重和干重显著降低,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著降低,而胞间CO2浓度以及丙二醛(MDA)、H2O2含量增加,超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性显著降低,抗坏血酸(AsA)和还原性谷胱甘肽(GSH)含量显著降低。(2)与NO3-胁迫处理相比,外源NaHS处理1、3、5d后,番茄幼苗的株高、根长、鲜重和干重显著增加,叶绿素(a、b)含量、净光合速率、气孔导度、蒸腾速率均显著升高,而胞间CO2浓度显著降低;MDA和H2O2含量降低,SOD、POD、CAT和APX活性显著增强,AsA和GSH含量显著增加,而且幼苗的硝酸还原酶、谷氨酰胺合成酶、谷氨酸合酶的活性显著增强;L-半胱氨酸脱巯基酶活性和内源H2S含量增加。研究认为,外源H2S可能通过提高抗氧化物酶的活性和增加抗氧化物质含量来缓解NO3-对番茄幼苗造成的伤害,从而增强其对NO3-胁迫耐性。     

Electro-Fenton,hydrogenotrophic and Fe2+ ions mediated TOC and nitrate removal from aquaculture system: Different experimental strategies

A number of methods for denitrification were studied including Electro-Fenton method, hydrogenotrophic as well as innovative Fe²⁺ mediated denitrification and their technical feasibility in terms of changes in TOC and nitrate concentrations, effect of different Fenton’s reagent dosage, current and the effect of the pH was investigated. This study was carried out using tailor made electrodialytic reactor. It was found that the highest TOC removal was achieved at pH 2.2 and 2.4 (77.1% and 97.8%, respectively) at the anode and the lowest accumulation of 33% at pH of 6.2 at the cathode. The highest TOC removal in terms of using different H₂O₂ concentrations was achieved at 40 mM reaching as high as 97.3%. Regardless experimental strategy, initially nitrates migrated towards the cathode due to the strong hydraulic gradient under the applied electric current. During the course of experiments, nitrates were transported towards the anode where their concentration decreased. The highest nitrate removal was achieved at 0.12 mA cm^?2 electric current density (94.8%) at the anode and a complete removal at the cathode. Hydrogenotrophic denitrification was the highest reaching 92.5%, however, when Fe²⁺ ions as electron donor was used for the destruction of nitrates, only 66.6% removal was achieved. Denitrification using only Fe²⁺ ions was a factor 1.4 less than using electrically generated hydrogen or a Fenton’s reagent.     

H2O2 Involvement in Polyamine-Induced Cell Death in Tobacco Leaf Discs

The response of tobacco (Nicotiana tabacum L.) wild-type SR1 leaf discs in terms of reactive oxygen species (ROS) formation and cell death occurrence was evaluated after exposure to the polyamines (PAs) putrescine (Put), spermidine (Spd), and spermine (Spm). Although NADPH oxidase-like enzyme activity was inhibited by all PAs at 3 or 21 h of treatment, H₂O₂ content increased significantly in a time- and concentration-dependent manner, suggesting that H₂O₂ accumulation was linked to the activity of other ROS-generating enzymes. Polyamine oxidase (PAO) activity, which increased markedly upon application of Spd or Spm, is a prime candidate for the increased H₂O₂ accumulation. Except for 0.1 mM Put, which maintained guaiacol peroxidase (GPOX) and catalase (CAT) activities at the same level as the control, the other PA treatments decreased CAT, ascorbate peroxidase, and GPOX activities at 21 h, contributing to the H₂O₂ increase. Esterase activity and Evans blue staining, two cell death parameters, were negatively affected at 3 h of treatment with 1 mM Spd and with both concentrations of Spm, whereas at 21 h there was an increase in cell death with both concentrations of the three PAs, except for 0.1 mM Put, which did not alter those parameters. The expression of the senescence-associated cysteine protease gene CP1 was measured to monitor senescence, a physiological cell death process. Application of all PAs increased the expression of the gene, except for 0.1 mM Put, which decreased its expression at 21 h. This result was in agreement with the prevention of cell death exerted by Put and evidenced by Evans blue staining, esterase activity, and electrolyte release.     

Simultaneous nitrification and denitrification with different mixed nitrogen loads by a hypothermia aerobic bacterium

Microorganism with simultaneous nitrification and denitrification ability plays a significant role in nitrogen removal process, especially in the eutrophic waters with excessive nitrogen loads. The nitrogen removal capacity of microorganism may suffer from low temperature or nitrite nitrogen source. In this study, a hypothermia aerobic nitrite-denitrifying bacterium, Pseudomonas tolaasii strain Y-11, was selected to determine the simultaneous nitrification and denitrification ability with mixed nitrogen source at 15 °C. The sole nitrogen removal efficiencies of strain Y-11 in simulated wastewater were obtained. After 24 h of incubation at 15 °C, the ammonium nitrogen fell below the detection limit from an initial value of 10.99 mg/L. Approximately 88.0 ± 0.33% of nitrate nitrogen was removed with the initial concentration of 11.78 mg/L and the nitrite nitrogen was not detected with the initial concentration of 10.75 mg/L after 48 h of incubation at 15 °C. Additionally, the simultaneous nitrification and denitrification nitrogen removal ability of P. tolaasii strain Y-11 was evaluated using low concentration of mixed NH₄⁺-N and NO₃^?–N/NO₂^?–N (about 5 mg/L-N each) and high concentration of mixed NH₄⁺–N and NO₃^?–N/NO₂^?–N (about 100 mg/L-N each). There was no nitrite nitrogen accumulation at the time of evaluation. The results demonstrated that P. tolaasii strain Y-11 had higher simultaneous nitrification and denitrification capacity with low concentration of mixed inorganic nitrogen sources and may be applied in low temperature wastewater treatment.     

Zingerone Protects Against Stannous Chloride-Induced and Hydrogen Peroxide-Induced Oxidative DNA Damage In Vitro

In this paper, we report the dose-dependent antioxidant activity and DNA protective effects of zingerone. At 500 μg/mL, the DPPH radical scavenging activity of zingerone and ascorbic acid as a standard was found to be 86.7 and 94.2 % respectively. At the same concentration, zingerone also showed significant reducing power (absorbance 0.471) compared to that of ascorbic acid (absorbance 0.394). The in vitro toxicity of stannous chloride (SnCl₂) was evaluated using genomic and plasmid DNA. SnCl₂-induced degradation of genomic DNA was found to occur at a concentration of 0.8 mM onwards with complete degradation at 1.02 mM and above. In the case of plasmid DNA, conversion of supercoiled DNA into the open circular form indicative of DNA nicking activity was observed at a concentration of 0.2 mM onwards; complete conversion was observed at a concentration of 1.02 mM and above. Zingerone was found to confer protection against SnCl₂-induced oxidative damage to genomic and plasmid DNA at concentrations of 500 and 750 μg/mL onwards, respectively. This protective effect was further confirmed in the presence of UV/H₂O₂-a known reactive oxygen species (ROS) generating system-wherein protection by zingerone against ROS-mediated DNA damage was observed at a concentration of 250 μg/mL onwards in a dose-dependent manner. This study clearly indicated the in vitro DNA protective property of zingerone against SnCl₂-induced, ROS-mediated DNA damage.     

Effects of Oxidation on Water Distribution and Physicochemical Properties of Porcine Myofibrillar Protein Gel

The effects of hydroxyl radicals induced oxidation on water distribution of porcine myofibrillar protein (MP) gels were investigated using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), and relationship between MP gel properties and water distribution was analyzed with Pearson’s correlation. Results of NMR spin-spin relaxation time (T₂) and MRI suggested that, comparing with unoxidized MP gel, the population of immobile water of gel (P₂₂) decreased by 18.81 %, while that of free water (P₂₃) increased by 85.56 %, and grey scale value decreased by 18.52 %, after being oxidized with 20 mM H₂O₂, respectively. Images of scanning electron microscope (SEM) showed the highest degree of oxidation led to the most coarse and porous gel-network. Gel properties including WHC, whiteness and strength of MP gels decreased by 14.65 %, 2.83 % and 52.74 % after being oxidized with 20 mM H₂O₂ (p?<?0.05), respectively. Pearson’s correlation analysis showed oxidation, gel-properties and NMR results were highly correlated (p?<?0.05). Therefore, we hypothesized that hydroxyl radicals induced oxidation resulted in immobile water shifting to free water partly, thus reduced the abundance of water and gel properties of gels.     

Role of enzymatic and non-enzymatic processes in H2O2 removal by rat liver and heart mitochondria

We compared the capacity of rat liver and heart mitochondria to remove exogenously produced H₂O₂, determining their ability to decrease fluorescence generated by H₂O₂ detector system. In the absence of substrates, liver and heart mitochondria removed H₂O₂ at similar rates. Respiratory substrate addition increased removal rates, indicating a respiration-dependent process. Moreover, the rates were higher with pyruvate/malate than with succinate and in heart than in liver mitochondria. Generally, the changes in H₂O₂ removal rates mirrored those of H₂O₂ release rates excluding the possibility that endogenous and exogenous H₂O₂ competed for the removing system. This idea was supported by the observation that the heaviest of three liver mitochondrial fractions exhibited the highest rates of both H₂O₂ release and removal. Pharmacological inhibition showed tissue-linked differences in antioxidant enzyme contribution to H₂O₂ removal which were consistent with the differences in antioxidant system activities. The enzymatic processes accounted only in part for net H₂O₂ removal and the non-enzymatic ones participated to H₂O₂ scavenging to a degree that was higher for heart than for liver mitochondria. The idea that non-enzymatic scavenging was due in great part to hemoproteins action was consistent with observation that the concentration of cytochromes, in particular cytochrome c, was higher in heart mitochondria. Indirect support was also obtained by a technique of enhanced luminescence, utilizing the capacity of cytochrome c/H₂O₂ to catalyze the luminol oxidation, which showed that luminescence response to an oxidative challenge was higher in heart mitochondria.     

Heterogeneous Catalytic Oxidation of Phenanthrene by Hydrogen Peroxide in Soil Slurry: Kinetics,Mechanism, and Implication

The degradation of phenanthrene sorbed on soil has been carried out using a H₂O₂/goethite heterogeneous catalytic oxidation process. The effect of operating variables, such as the goethite concentration, pH, H₂O₂ concentration, soil organic matter, and bicarbonate ions has been investigated. The reaction followed pseudo-first order kinetics. The rate constants were evaluated and varied between 2.0×10^?4 and 1.1×10^?3?min^?1 depending on the H₂O₂ concentration. The highest rate of degradation of phenanthrene was observed at a H₂O₂ concentration of 5?M and 134.0?g/kg goethite. The intermediate product formed during the degradation of phenanthrene was identified to be salicylic acid that finally degraded to CO₂ and H₂O. H₂O₂ consumption continued as the OH radical attacked the salicylic acid. More than 80% consumption of the 5?M H₂O₂ took place within 30?min, and the degradation was almost complete after 3?h of reaction. Neutral pH was found to be effective in the removal of phenanthrene. Both soil organic matter (SOM) and bicarbonate ions in the soil inhibited the oxidation rate of phenanthrene.