Gene expression modulation by chalcopyrite and bornite in Acidithiobacillus ferrooxidans

Acidithiobacillus ferrooxidans is a mesophilic, acidophilic, chemolithoautotrophic bacterium that obtains energy from the oxidation of ferrous iron (Fe²⁺), elemental sulfur and reduced sulfur compounds. The industrial interest in A. ferrooxidans resides in its capacity to oxidize insoluble metal sulfides into soluble metal sulfates, thus allowing the recovery of the desired metals from low-grade sulfide ores. In the present work, RNA arbitrarily primed PCR (RAP-PCR) was performed to identify cDNAs differentially expressed in A. ferrooxidans cells grown in the presence of Fe²⁺ and cells maintained for 24 h in the presence of the copper sulfides bornite and chalcopyrite. Eighteen cDNAs corresponding to genes with known function were identified, and their relative expression was further characterized by real-time quantitative PCR. Bornite had a mild effect on the expression of the 18 genes analyzed. None of these genes was down-regulated and among the few genes up-regulated, it is worth mentioning lepA and def-2 that are involved in protein synthesis. Chalcopyrite presented the most significant changes. Five genes related to protein processing were down-regulated, and another 5 genes related to the transport system were up-regulated. The up- and down-regulation of these genes in the presence of bornite and chalcopyrite could be due to alterations in the ideal pH, presence of copper ions in solution and nutrient limitation. The results suggest that gene expression modulation might be important for the A. ferrooxidans early response to copper sulfides.     

Dehydroascorbate reductase and glutathione reductase play an important role in scavenging hydrogen peroxide during natural and artificial dehydration of Jatropha curcas seeds

Changes in H₂O₂ and the main antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), in endospermic and embryonic tissues were studied in developing and artificially dried Jatropha curcas seeds. Immature seeds were desiccation-tolerant at 80 days after flowering, as they were able to germinate fully after artificial drying on silica gel had reduced their water content to 10–12% of fresh weight. In both endospermic and embryonic tissues, H₂O₂ level and, consequently, lipid peroxide content, decreased during seed development as well as after artificial dehydration of developing seeds. All examined antioxidant enzymes except DHAR showed a decrease in total activity in mature stages as compared with early stages. Expression analysis of SOD genes revealed that the decrease in total SOD activities was related to the decrease in Cu/Zn-SOD expression, while the continuous activity of SOD during maturation was related to an increase in Mn-SOD expression. Artificial drying resulted in increased SOD and DHAR activity, irrespective of the developmental stage. Our results revealed weak participation of CAT and APX in H₂O₂ scavenging, as well as no significant alterations in GR activities either during maturation or after artificial drying. Changes in SOD and GR isoenzyme patterns occurred during maturation-related drying, but not after artificial drying. These results highlight the role of ascorbate-glutathione cycle enzymes (DHAR and GR) in H₂O₂ scavenging during maturation or after artificial drying of developing J. curcas seeds.     

Inhibition of Both Thioredoxin Reductase and Glutathione Reductase may Contribute to the Anticancer Mechanism of TH-302

Selenium-containing thioredoxin reductase (TrxR) is an important target of cancer therapy. Many useful anticancer agents including bis-alkylating agents, cisplatin, and arsenic trioxide are known to interact with the selenocysteine dipeptide in the carboxy terminal region of thioredoxin reductase and inactivate its ability to reduce thioredoxin. Some investigators have postulated that the inactivation of TrxR may add to the cytotoxic potential of these anticancer agents. TH-302 is a newly developed antineoplastic drug which represents a potential new class of tumor selective hypoxia-activated prodrugs (HAPs). TH-302 is an inactive prodrug created by the covalent conjugation of 2-nitroimidazole as an oxygen sensor to bromo-isophosphoramide (Br-IPM). In the presence of severe hypoxia and near anoxia, the two imidazole sensor moiety undergoes reduction and the Br-IPM is released in situ. Bromo-IPM is a more potential analog of Chloro-IPM, the active alkylating moiety that is derived by activation of ifosfamide (IFO). We previously demonstrated that IFO could inhibit tumor TrxR activity and chloro-IPM is known to bind covalently to the seleno-cysteine dipeptide in thioredoxin reductase. The present study assessed the ability of TH-302 to activate in the tumors of mice-bearing hepatoma 22 (H22) and inactivate the tumor TrxR. In mice-bearing hepatoma 22 (H22) solid tumors, intraperitoneal (i.p.) injection with TH-302 at the dose of 200 mg/kg administered twice, a regimen which was well tolerated by the mice, significantly inhibited tumor growth. Also in this mice model, i.p. TH-302 at the dose of 300 mg/kg, which would be the maximum single i.p. administration dose tolerated by mice, and which induced only 2% body weight loss, significantly inhibited both TrxR and glutathione reductase (GR) activities by 46% (P?<?0.001) and 60% (P?<?0.001) as compared with the controls, respectively, at 3 h after the injection. Since TrxR is a key player in thioredoxin system and GR is the major reductase for the reduction of oxidized glutathione in glutathione system, the present results imply the anticancer effect of TH-302 is associated concurrently with modulation of TrxR and GR. These findings suggest that the anticancer activity of TH-302 in this model system may associate with both DNA alkylation and the modulation of TrxR and GR. In addition, they suggest that, by inhibition of these two critical reductases, with less glutathione available to intercept the reactive intermediates involved in DNA alkylation, the antitumor effects of the chemotherapy would be enhanced.     

Diphenyl ditelluride targets brain selenoproteins in vivo: inhibition of cerebral thioredoxin reductase and glutathione peroxidase in mice after acute exposure

In this study, we investigated the effect of diphenyl ditelluride (PhTe)₂ administration (10 and 50?μmol/kg) on adult mouse behavioral performance as well as several parameters of oxidative stress in the brain and liver. Adult mice were injected with (PhTe)₂ or canola oil subcutaneously (s.c.) daily for 7?days. Results demonstrated that (PhTe)₂ induced prominent signs of toxicity (body weight loss), behavioral alterations and increased in lipid peroxidation in brain. 50?μmol/kg (PhTe)₂ inhibited blood δ-aminolevulinic acid dehydratase (δ-ALA-D), a redox sensitive enzyme. (PhTe)₂ caused an increase in cerebral non-protein thiol (NPSH) and protein thiol (PSH) groups. In the liver, 50?μmol/kg (PhTe)₂ decreased NPSH, but did not alter the content of protein thiol groups. (PhTe)₂ decreased cerebral antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD), glutathione reductase (GR), glutathione peroxidase (GPx), and thioredoxin reductase (TrxR). In liver, (PhTe)₂ increase SOD and GR and decreased GPx activity. Results obtained herein suggest that the brain was more susceptible to oxidative stress induced by (PhTe)₂ than the liver. Furthermore, we have demonstrated for the first time that TrxR is an in vivo target for (PhTe)_2. Combined, these results highlight a novel molecular mechanism involved in the toxicity of (PhTe)₂. In particular the inhibition of important selenoenzymes (TrxR and GPx) seems to be involved in the neurotoxicity associated with (PhTe)₂ exposure in adult mice.     

Response of antioxidant enzymes to transfer from elevated carbon dioxide to air and ozone fumigation, in the leaves and roots of wild‐type and a catalase‐deficient mutant of barley

A catalase-deficient mutant (RPr 79/4) and the wild-type (cv. Maris Mink) barley (Hordeum vulgare L.) counterpart, were grown for 3 weeks in high CO₂ (0.7%) and then transferred to air and ozone (120 nl 1^?1) in the light and shade for a period of 4 days. Leaves and roots were analysed for catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and glutathione reductase (GR, EC 1.6.4.2) activities. CAT activity in the leaves of the RPr 79/4 catalase-deficient mutant was around 5-10% of that determined in Maris Mink, but in the roots, both genotypes contained approximately the same levels of activity. CAT activity in Maris Mink increased in the leaves after transferring plants from 0.7% CO₂ to air or ozone, reaching a maximum of 5-fold, after 4 days in shade and ozone. For the catalase-deficient mutant, only small increases in CAT activity were observed in light/air and light/ozone treatments. In the roots, CAT activity decreased consistently in both genotypes, after plants were transferred from 0.7% CO₂. The total soluble SOD activity in the leaves and roots of both genotypes increased after plants were transferred from 0.7% CO₂. The analysis of SOD isolated from leaves following non-denaturing PAGE, revealed the presence of up to eight SOD isoenzymes classified as Mn-SOD or Cu/Zn-SODs; Fe-SOD was not detected. Significant changes in Mn- and Cu/Zn-SOD isoenzymes were observed; however, they could not account for the increase in total SOD activity. In leaves, GR activity also increased in Maris Mink and RPr 79/4, following transfer from 0.7% CO₂; however, no constant pattern could be established, while in roots, GR activity was reduced after 4 days of the treatments. The data suggest that elevated CO₂ decreases oxidative stress in barley leaves and that soluble CAT and SOD activities increased rapidly after plants were transferred from elevated CO₂, irrespective of the treatment (light, shade, air or ozone).     

Effect of thioredoxin reductase 1 on glucocorticoid receptor activity in human outer root sheath cells

Alopecia areata (AA) is a common disease of patchy hair loss on the scalp that can progress to cover the entire scalp and eventually the entire body. Intralesional injection of corticosteroids is the first-line therapy for adult patients, however some patients do not respond to glucocorticoid treatment effectively. To delineate the molecular mechanism underlying glucocorticoid insensitivity, we examined the expression of glucocorticoid receptor (GR) and thioredoxin reductase 1 (TrxR1). In some case of glucocorticoid-resistant AA patients, the expression of TrxR1 was decreased in outer root sheath (ORS). We then investigated the effect of TrxR1 on GR activity using recombinant adenoviruses. Overexpression of TrxR1 markedly increased GR activity in ORS cells cultured in vitro. In addition, TrxR1 protected GR activity against H(2)O(2). Finally, TrxR1-enhanced GR activity was significantly inhibited by the overexpression of dominant negative form of Trx (Trx(C32S/C35S)). These results suggest that decreased TrxR1 may be one putative cause for glucocorticoid resistance in AA, through the impact on intracellular redox system.     

Effect of cold acclimation on the antioxidant defense system of two larval lepidoptera (noctuidae)

Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), glutathione-S-transferase (GST), as well as total glutathione (tGSH) concentration were analyzed in the hemolymph and fat body of the European corn borer Ostrinia nubilalis Hubn. and the Mediterranean borer Sesamia cretica Led. (Lepidoptera, Noctuidae). Controls were maintained at 8°C while experimental groups of larvae were exposed to –3°C for ten days and then to –12°C for 23 days (only for Ostrinia). Cold exposure significantly increased fat body SOD, GR, and GST activities of Ostrinia larvae. Only GST activity and tGSH levels increased significantly in Ostrinia larval hemolymph on cold exposure. In Sesamia larvae after cold exposure, hemolymph CAT activity was significantly lower, while fat body tGSH increased. The antioxidant defense systems of these two species show differences, probably influenced by their respective cold-hardiness metabolism. According to its antioxidant profile, the response of Ostrinia suggests a significant physiological alteration in its metabolism during cold exposure, indicating a compensatory mechanism. By contrast this is not evident in Sesamia.Arch. Insect Biochem. Physiol. 36:1–10, 1997. © 1997 Wiley-Liss, Inc.     

Selective Adhesion of Thiobacillus ferrooxidans to Pyrite

Bacterial adhesion to mineral surfaces plays an important role not only in bacterial survival in natural ecosystems, but also in mining industry applications. Selective adhesion was investigated with Thiobacillus ferrooxidans by using four minerals, pyrite, quartz, chalcopyrite, and galena. Escherichia coli was used as a control bacterium. Contact angles were used as indicators of hydrophobicity, which was an important factor in the interaction between minerals and bacteria. The contact angle of E. coli in a 0.5% sodium chloride solution was 31°, and the contact angle of T. ferrooxidans in a pH 2.0 sulfuric acid solution was 23°. E. coli tended to adhere to more hydrophobic minerals by hydrophobic interaction, while T. ferrooxidans selectively adhered to iron-containing minerals, such as pyrite and chalcopyrite. Ferrous ion inhibited the selective adhesion of T. ferrooxidans to pyrite competitively, while ferric ion scarcely inhibited such adhesion. When selective adhesion was quenched by ferrous ion completely, adhesion of T. ferrooxidans was controlled by hydrophilic interactions. Adhesion of E. coli to pyrite exhibited a liner relationship on langmuir isotherm plots, but adhesion of T. ferrooxidans did not. T. ferrooxidans recognized the reduced iron in minerals and selectively adhered to pyrite and chalcopyrite by a strong interaction other than the physical interaction.     

Oxidative damage and antioxidant defense system in leaves of Vicia faba major L. cv. Bartom during soil flooding and subsequent drainage

The adaptive reactions of Vicia faba major L. cv. Bartom to 13-27 days soil flooding and to 14 days of drainage following 13-days of soil flooding were studied. Under flooding, oxygen diffusion rate (ODR) in the root zone decreased from 2.28–3.44 to 0.09–0.28?µmol O₂ m^?2 s^?1; the soil redox potential (Eh) decreased from 543 to 70 mV. Upon drainage of flooded soil the ODR and Eh values returned to the control levels. Oxidative damage and defense systems in leaves were assessed by the concentration of thiobarbituric acid reactive substances (TBARs) and by the activities of superoxide dismutase (SOD) and glutathione reductase (GR). Two stages of stress development are described. During the first stage (1–13 days) shoot dry mass did not decrease, the TBARs concentration and SOD activity increased, the GR activity decreased. The second stage (13–27 days) was characterized by a decrease in the TBARs concentration, SOD and GR activities, pigment concentrations and shoot dry mass. Drainage of flooded soil resulted in elevated concentrations of TBARs and also increased the activities of SOD and GR. Increased SOD activity in the first stage of hypoxic stress development and activations of SOD and GR at oxygen re-entry to soil are responsible for tolerance of Vicia faba to hypoxic and post hypoxic stress associated with soil flooding and subsequent drainage.     

Maternal cadmium intoxication: effects on fetal brain antioxidant defense parameters

Summary

The antioxidant potential of the brain in developing fetuses was assessed at gestational days (GD) 16, 18 and 20 and postnatal day (PND)1. Higher activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were noticed during fetal development which were reduced to about half and one-quarter, respectively, at PND 1. Glutathione reductase (GR) activity remained stationary throughout the experiment and the values were very high compared to those reported for weanling rats. In contrast, catalase (CAT) activity increased with development. Glutathione (GSH) and total sulfhydryls (TSH) were maximum in 16-day fetal brains and declined subsequently. Brain lipid peroxidation (LPO) was found to increase with age. A group of animals was exposed to 20 ppm cadmium (Cd) in drinking water from the day of conception up to PND 1. Cd was found to increase the activities of brain SOD, CAT, and GR significantly at all the time intervals. The metal exposure decreased fetal brain GPx at GD 18 and 20, whereas GPx activity declined precipitously in both groups on PND 1. Cd caused both increments and decrements in the GSH and TSH levels (depending on gestational day) and increased the LPO in brain. It may be concluded that the Cd-intoxicated fetal brain undergoes significant changes in antioxidant defense parameters which, overall, may be sufficient to permit near-normal development and prevent substantial oxidant damage.     

Cooperative action of antioxidant defense systems in Drosophila

Molecular oxygen is key to aerobic life but is also converted into cytotoxic byproducts referred to as reactive oxygen species (ROS). Intracellular defense systems that protect cells from ROS-induced damage include glutathione reductase (GR), thioredoxin reductase (TrxR), superoxide dismutase (Sod), and catalase (Cat). Sod and Cat constitute an evolutionary conserved ROS defense system against superoxide; Sod converts superoxide anions to H(2)O(2), and Cat prevents free hydroxyl radical formation by breaking down H(2)O(2) into oxygen and water. As a consequence, they are important effectors in the life span determination of the fly Drosophila. ROS defense by TrxR and GR is more indirect. They transfer reducing equivalents from NADPH to thioredoxin (Trx) and glutathione disulfide (GSSG), respectively, resulting in Trx(SH)(2) and glutathione (GSH), which act as effective intracellular antioxidants. TrxR and GR were found to be molecularly conserved. However, the single GR homolog of Drosophila specifies TrxR activity, which compensates for the absence of a true GR system for recycling GSH. We show that TrxR null mutations reduce the capacity to adequately protect cells from cytotoxic damage, resulting in larval death, whereas mutations causing reduced TrxR activity affect pupal eclosion and cause a severe reduction of the adult life span. We also provide genetic evidence for a functional interaction between TrxR, Sod1, and Cat, indicating that the burden of ROS metabolism in Drosophila is shared by the two defense systems.     

Cytological and physiological changes in orthodox maize embryos during cryopreservation

Cytological and physiological changes during cryopreservation were studied in maize embryos at 35 days after pollination (DAP). Both dehydration and freezing caused cytological damage, such as plasmolysis, swelled mitochondria, increased heterochromatin, and nuclear shrinkage. Dehydration alone slightly impaired plasma membrane integrity while a drastic increase in electrolyte leakage was observed after freezing of embryos with moisture content above 23%. Damage to cellular ultrastructure and plasmalemma integrity was negatively related to moisture content in unfrozen embryos and positively related in frozen embryos. The pattern of changes in activity of antioxidant enzymes differed from one another during dehydration and/or freezing–thawing treatment. Dehydration increased activity of ascorbate peroxidase (APX) and glutathione reductase (GR) but decreased activity of superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR). Freezing further decreased GR and SOD activity and resulted in extremely low DHAR activity. Embryos at intermediate moisture contents had low catalase (CAT) activity before freezing but highest CAT activity after freeze–thaw. Both dehydration and freezing promoted membrane lipid peroxidation which resulted in an approximately threefold increase at most in the malondialdehyde content in postthaw embryos. Changes in viability of postthaw embryos can be closely related to damage in cellular ultrastructure and plasmalemma integrity but directly related neither to antioxidants nor lipid peroxidation levels.     

Attachment of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum cultured under varying conditions to pyrite, chalcopyrite, low-grade ore and quartz in a packed column reactor

The attachment of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum spp. grown on ferrous medium or adapted to a pyrite mineral concentrate to four mineral substrata, namely, chalcopyrite and pyrite concentrates, a low-grade chalcopyrite ore (0.5 wt%) and quartzite, was investigated. The quartzite represented a typical gangue mineral and served as a control. The attachment studies were carried out in a novel particle-coated column reactor. The saturated reactor containing glass beads, which were coated with fine mineral concentrates, provided a quantifiable surface area of mineral concentrate and maintained good fluid flow. A. ferrooxidans and Leptospirillum spp. had similar attachment characteristics. Enhanced attachment efficiency occurred with bacteria grown on sulphide minerals relative to those grown on ferrous sulphate in an ore-free environment. Selective attachment to sulphide minerals relative to gangue materials occurred, with mineral adapted cultures attaching to the minerals more efficiently than ferrous grown cultures. Mineral-adapted cultures showed highest levels of attachment to pyrite (74% and 79% attachment for A. ferrooxidans and L. ferriphilum, respectively). This was followed by attachment of mineral-adapted cultures to chalcopyrite (63% and 58% for A. ferrooxidans and L. ferriphilum, respectively). A. ferrooxidans and L. ferriphilum exhibited lower levels of attachment to low-grade ore and quartz relative to the sulphide minerals.     

Simvastatin inhibits the core promoter of the TXNRD1 gene and lowers cellular TrxR activity in HepG2 cells

Thioredoxin reductase 1 (TrxR1) is a selenocysteine-containing redox-active enzyme that is thought to be important during carcinogenesis. We have recently shown that treatment with statins, HMGCoA reductase inhibitors, reduces the levels of TrxR1 in liver of both rat and human. The reduced TrxR1 levels were correlated with inhibited hepatocarcinogenesis in a rat model. The aim of the present study was to investigate if statins affect the activity of the human TXNRD1 core promoter, which guides expression of TrxR1, and if the effects by statins on TrxR1 expression in liver could be reproduced in a cellular model system. We found that simvastatin and fluvastatin decreased cellular TrxR activity in cultured human liver-derived HepG2 cells with approximately 40% (p < 0.05). Simvastatin, but not fluvastatin or atorvastatin, also reduced the TXNRD1 promoter activity in HepG2 cells by 20% (p < 0.01). In line with this result, TrxR1 mRNA levels decreased with about 25% in non-transfected HepG2 cells upon treatment with simvastatin (p < 0.01). Concomitant treatment with mevalonate could not reverse these effects of simvastatin, indicating that other mechanisms than HMGCoA reductase inhibition was involved. Also, simvastatin did not inhibit sulforaphane-derived stimulation of the TXNRD1 core promoter activity, suggesting that the inhibition by simvastatin was specific for basal and not Nrf2-activated TrxR1 expression. In contrast to simvastatin, the two other statins tested, atorvastatin or fluvastatin, did not influence the TrxR1 mRNA levels. Thus, our results reveal a simvastatin-specific reduction of cellular TrxR1 levels that at least in part involves direct inhibitory effects on the basal activity of the core promoter guiding TrxR1 expression.     

OXIDIZED LIPIDS DID NOT REDUCE LIFESPAN IN THE FRUIT FLY,Drosophila melanogaster

Aging is often associated with accumulation of oxidative damage in proteins and lipids. However, some studies do not support this view, raising the question of whether high levels of oxidative damage are associated with lifespan. In the current investigation, Drosophila melanogaster flies were kept on diets with 2 or 10% of either glucose or fructose. The lifespan, fecundity, and feeding as well as amounts of protein carbonyls (PC) and lipid peroxides (LOOH), activities of superoxide dismutase (SOD), catalase, glutathione‐S‐transferase (GST), and glutathione reductase activity of thioredoxin reductase (TrxR) were measured in “young” (10‐day old) and “aged” (50‐day old) flies. Flies maintained on diets with 10% carbohydrate lived longer than those on the 2% diets. However, neither lifespan nor fecundity was affected by the type of carbohydrate. The amount of PC was unaffected by diet and age, whereas flies fed on diets with 10% carbohydrate had about fivefold higher amounts of LOOH compared to flies maintained on the 2% carbohydrate diets. Catalase activity was significantly lower in flies fed on diets with 10% carbohydrates compared to flies on 2% carbohydrate diets. The activities of SOD, GST, and TrxR were not affected by the diet or age of the flies. The higher levels of LOOH in flies maintained on 10% carbohydrate did not reduce their lifespan, from which we infer that oxidative damage to only one class of biomolecules, particularly lipids, is not sufficient to influence lifespan.     

Involvement of antioxidant defense system in chill hardening-induced chilling tolerance in Jatropha curcas seedlings

Jatropha curcas L. is a sustainable energy plant with great potential for biodiesel production, and low temperature is an important limiting factor for its distribution and production. In this present work, chill hardening-induced chilling tolerance and involvement of antioxidant defense system were investigated in J. curcas seedlings. The results showed that chill hardening at 10 or 12 °C for 1 and 2 days greatly lowered death rate and alleviated electrolyte leakage as well as accumulation of the lipid peroxidation product malondialdehyde (MDA) of J. curcas seedlings under severe chilling stress at 1 °C for 1–7 days, indicating that the chill hardening significantly improved chilling tolerance of J. curcas seedlings. Measurement of activities of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and glutathione reductase (GR), and the levels of the antioxidants ascorbic acid (AsA) and glutathione (GSH) showed the chill hardening at 12 °C for 2 days could obviously increase the activities of these antioxidant enzymes and AsA and GSH contents in the hardened seedlings. When the hardened and non-hardening (control) seedlings were subjected to severe chilling stress at 1 °C for 1–7 days, the chill-hardened seedlings generally maintained significantly higher activities of the antioxidant enzymes SOD, APX, CAT, POD, and GR, and content of the antioxidants AsA and GSH as well as ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)], when compared with the control without chill hardening. All above-mentioned results indicated that the chill hardening could enhance the chilling tolerance, and the antioxidant defense system plays an important role in the chill hardening-induced chilling tolerance in J. curcas seedlings.     

The effect of astaxanthin and cadmium on rat erythrocyte G6PD, 6PGD,GR, and TrxR enzymes activities in vivo and on rat erythrocyte 6PGD enzyme activity in vitro

In this study, the effects of astaxanthin (AST) that belongs to carotenoid family and cadmium (Cd), which is an important heavy metal, on rat erythrocyte G6PD, 6PGD, GR, and TrxR enzyme activities in vivo and on rat erythrocyte 6PGD enzyme activity in vitro were studied. In in vitro studies, 6PGD enzyme was purified from rat erythrocytes with 2′,5′‐ADP Sepharose4B affinity chromatography. Results showed inhibition of enzyme by Cd at IC₅₀; 346.5 μM value and increase of 6PGD enzyme activity by AST. In vivo studies showed an increase in G6PD, 6PGD, and GR enzyme activities (P ? 0.05) and no chance in TrxR enzyme activity by AST. Cd ion inhibited G6PD, 6PGD, and GR enzyme activities (P ? 0.05) and also decreased TrxR enzyme activity (P ? 0.05). AST + Cd group G6PD enzyme activity was statistically low compared with control group (P ? 0.05). 6PGD and TrxR enzyme activities decreased without statistical significance (P ? 0.05); however, GR enzyme activity increased statistically significantly (P ? 0.05).     

Bioleaching of chalcopyrite by pure and mixed cultures of Acidithiobacillus spp. and Leptospirillum ferriphilum

Bioleaching is an economical method for the recovery of metals that requires low investment and operation costs. Furthermore, it is generally more environmentally friendly than many physicochemical metal extraction processes. The bioleaching of chalcopyrite in shake flasks was investigated with pure and mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Acidithiobacillus caldus, and Leptospirillum ferriphilum. The mixed cultures containing both iron- and sulfur-oxidizing bacteria were more efficient than the pure culture alone. The presence of sulfur-oxidizing bacteria positively increased the dissolution rate and the percentage recovery of copper from chalcopyrite. Mixed cultures consisting of moderately thermophilic L. ferriphilum and A. caldus leached chalcopyrite more effectively than mesophilic A. ferrooxidans pure and mixed cultures. The decrease of the chalcopyrite dissolution rate in leaching systems containing A. ferrooxidans after 12–16 days coincided with the formation of jarosite precipitation as a passivation layer on the mineral surface during bioleaching. Low pH significantly reduces jarosite formation in pure and mixed cultures of L. ferriphilum and A. caldus.