Anaerobic Microbial Dissolution of Transition and Heavy Metal Oxides

Anaerobic microbial dissolution of several crystalline, water-insoluble forms of metal oxides commonly associated with the waste from energy production was investigated. An anaerobic N-fixing Clostridium sp. with an acetic, butyric, and lactic acid fermentation pattern, isolated from coal-cleaning waste, solubilized Fe₂O₃ and MnO₂ by direct enzymatic reduction; CdO, CuO, PbO, and ZnO were solubilized by indirect action due to the production of metabolites and the lowering of the pH of the growth medium. Extracellular heat-labile components of the cell-free spent medium obtained from cultures without oxide solubilized a significant amount of Fe₂O₃ (1.7 μmol); however, direct contact with the bacterial cells resulted in the complete dissolution (4.8 μmol) of the oxide. Under identical conditions, the cell-free spent medium solubilized only a small amount of MnO₂ (0.07 μmol), whereas 2.3 μmol of the oxide was solubilized by direct bacterial contact. Reduction of Fe₂O₃ and MnO₂ by Clostridium sp. proceeds at different rates and, possibly, by different enzymatic systems. Fe(III) and Mn(IV) oxides appear to be used as sinks for excess electrons generated from glucose fermentation, since there is no apparent increase in growth of the bacterium concomitant with the reduction of the oxides. Dialysis bag experiments with Co₂O₃ indicate that there is a slight dissolution of Co (0.16 μmol) followed by precipitation or biosorption. Although Mn₂O₃, Ni₂O₃, and PbO₂ may undergo reductive dissolution from a higher to a lower oxidation state, dissolution by direct or indirect action was not observed. Also, Cr₂O₃ and NiO were not solubilized by direct or indirect action. Significant amounts of solubilized Cd, Cu, and Pb were immobilized by the bacterial biomass, and the addition of Cu²⁺ inhibited the growth of the bacterium.     

Determination of the growth and solubilization capabilities of <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> T1

The growth capability of Trichoderma harzianum Rifaii Tl was tested on Malt Extract and Czapeks Dox agar containing different concentrations of Cu²⁺, Zn²⁺, Mn²⁺, Fe²⁺ and Ca²⁺. The T. harzianum Tl isolate was observed to produce mycelia and spores in various mineral-containing media. It showed the lowest tolerance to Ca²⁺ and the highest tolerance to Fe²⁺. Solubilization capability of T. harzianum Tl for some insoluble minerals via acidification of medium has been tested on MnO₂, CuO, Fe₂O₃ and metallic Zn. T. harzianum Tl was able to solubilize MnO₂ and metallic Zn in a liquid medium.     

Expressing a gene encoding wheat oxalate oxidase enhances resistance to Sclerotinia sclerotiorum in oilseed rape (Brassica napus)

Sclerotinia sclerotiorum causes a highly destructive disease in oilseed rape (Brassica napus). Oxalic acid (OA) secreted by the pathogen is a key pathogenicity factor. Oxalate oxidase (OXO) can oxidize OA into CO₂ and H₂O₂. In this study, we show that transgenic oilseed rape (sixth generation lines) constitutively expressing wheat (Triticum aestivum) OXO displays considerably increased OXO activity and enhanced resistance to S. sclerotiorum (with up to 90.2 and 88.4% disease reductions compared with the untransformed parent line and a resistant control, respectively). Upon application of exogenous OA, the pH values in transgenic plants were maintained at levels slightly lower than 5.58 measured prior to OA treatment, whereas the pH values in untransformed plants decreased rapidly and were markedly lower than 5.63 measured prior to OA treatment. Following pathogen inoculation, H₂O₂ levels were higher in transgenic plants than in untransformed plants. These results indicate that the enhanced resistance of the OXO transgenic oilseed rape to Sclerotinia is probably mediated by OA detoxification. We believe that enhancing the OA metabolism of oilseed rape in this way will be an effective strategy for improving resistance to S. sclerotiorum. Xiangbai Dong and Ruiqin Ji contributed equally to this paper.     

Effect of environmental factors and precursors on oxalic acid production,mycelial biomass and virulence of a potential bioherbicide isolate of Sclerotium rolfsii SC64 produced in liquid culture

The fungus Sclerotium rolfsii is presently under development as a bioherbicide for broadleaf weed species using fungus-infested substrates as application material in this laboratory. The effect of environmental factors and three precursors (citric acid, ascorbic acid, and sodium succinate) on mycelial growth, oxalic acid production, and virulence by SC64 in liquid culture were investigated. The results showed that for mycelia growth the optimum liquid medium was Modified Richard's solution (MRS) among the five tested media, but potato dextrose broth (PDB) produced the maximum oxalic acid production and virulence on detached Solidago canadensis leaves. When PDB was used as the basic medium, the oxalic acid/mycelial dry weight (mg g^–1) ratio reached the peak 4 days after inoculation. The optimum temperature for oxalic acid production was at 27°C, but increased mycelial dry weight and virulence were observed at 30°C. The optimum range of initial pH value for oxalic acid accumulation was 4.0–6.0, with the optimal pH 5.0; highest mycelial growth was with an initial pH 3.5–6.0 (optimum pH 5.0) and subsequently pH 3.5–5.5 (maximum at pH 3.5). Both mycelial dry weight and oxalic acid production showed a decreasing trend as a result of the precursor of oxalic acid being added to PDB. Among the three precursors, the greatest decrease in mycelial dry weight, and oxalic acid production was caused by sodium succinate. This clarification of optimal conditions for production of mycelial biomass while insuring high concentrations of oxalic acid and high virulence should be useful for further development of this fungus as biocontrol agent.     

Synthesis,Characterization, and Structural Modeling of High‐Capacity,Dual Functioning MnO2 Electrode/Electrocatalysts for Li‐O2 Cells

It has become clear that cycling lithium‐oxygen cells in carbonate electrolytes is impractical, as electrolyte decomposition, triggered by oxygen reduction products, dominates the cell chemistry. This research shows that employing an α‐MnO₂/ramsdellite‐MnO₂ electrode/electrocatalyst results in the formation of lithium‐oxide‐like discharge products in propylene carbonate, which has been reported to be extremely susceptible to decomposition. X‐ray photoelectron data have shown that what are likely lithium oxides (Li₂O₂ and Li₂O) appear to form and decompose on the air electrode surface, particularly at the MnO₂ surface, while Li₂CO₃ is also formed. By contrast, cells without α‐MnO₂/ramsdellite‐MnO₂ fail rapidly in electrochemical cycling, likely due to the differences in the discharge product. Relatively high electrode capacities, up to 5000 mAh/g (carbon + electrode/electrocatalyst), have been achieved with non‐optimized air electrodes. Insights into reversible insertion reactions of lithium, lithium peroxide (Li₂O₂) and lithium oxide (Li₂O) in the tunnels of α‐MnO₂, and the reaction of lithium with ramsdellite‐MnO₂, as determined by first principles density functional theory calculations, are used to provide a possible explanation for some of the observed results. It is speculated that a Li₂O‐stabilized and partially‐lithiated electrode component, 0.15Li₂O·α‐Li_xMnO₂, that has Mn^4+/3+ character may facilitate the Li₂O₂/Li₂O discharge/charge chemistries providing dual electrode/electrocatalyst functionality.     

Defect Engineering of Oxygen‐Deficient Manganese Oxide to Achieve High‐Performing Aqueous Zinc Ion Battery

A major limitation of MnO₂ in aqueous Zn/MnO₂ ion battery applications is the poor utilization of its electrochemical active surface area. Herein, it is shown that by generating oxygen vacancies (V_O) in the MnO₂ lattice, Gibbs free energy of Zn²⁺ adsorption in the vicinity of V_O can be reduced to thermoneutral value (≈0.05 eV). This suggests that Zn²⁺ adsorption/desorption process on oxygen‐deficient MnO₂ is more reversible as compared to pristine MnO₂. In addition, because of the fact that fewer electrons are needed for Zn? O bonding in oxygen‐deficient MnO₂, more valence electrons can be contributed into the delocalized electron cloud of the material, which aids in enhancing the attainable capacity. As a result, the stable Zn/oxygen‐deficient MnO₂ battery is able to deliver one of the highest capacities of 345 mAh g^?1 reported for a birnessite MnO₂ system. This excellent electrochemical performance suggests that generating oxygen vacancies in MnO₂ may aid in the future development of advanced cathodes for aqueous Zn ion batteries.     

Overexpression of a gene encoding hydrogen peroxide-generating oxalate oxidase evokes defense responses in sunflower

Oxalate oxidase (OXO) converts oxalic acid (OA) and O(2) to CO(2) and hydrogen peroxide (H(2)O(2)), and acts as a source of H(2)O(2) in certain plant-pathogen interactions. To determine if the H(2)O(2) produced by OXO can function as a messenger for activation of defense genes and if OXO can confer resistance against an OA-producing pathogen, we analyzed transgenic sunflower (Helianthus annuus cv SMF3) plants constitutively expressing a wheat (Triticum aestivum) OXO gene. The transgenic leaf tissues could degrade exogenous OA and generate H(2)O(2). Hypersensitive response-like lesion mimicry was observed in the transgenic leaves expressing a high level of OXO, and lesion development was closely associated with elevated levels of H(2)O(2), salicylic acid, and defense gene expression. Activation of defense genes was also observed in the transgenic leaves that had a low level of OXO expression and had no visible lesions, indicating that defense gene activation may not be dependent on hypersensitive response-like cell death. To further understand the pathways that were associated with defense activation, we used GeneCalling, an RNA-profiling technology, to analyze the alteration of gene expression in the transgenic plants. Among the differentially expressed genes, full-length cDNAs encoding homologs of a PR5, a sunflower carbohydrate oxidase, and a defensin were isolated. RNA-blot analysis confirmed that expression of these three genes was significantly induced in the OXO transgenic sunflower leaves. Furthermore, treatment of untransformed sunflower leaves with jasmonic acid, salicylic acid, or H(2)O(2) increased the steady-state levels of these mRNAs. Notably, the transgenic sunflower plants exhibited enhanced resistance against the OA-generating fungus Sclerotinia sclerotiorum.     

Organic acids production by white rot Basidiomycetes in the presence of metallic oxides

The purpose of the present work was to determine if selected fungal strains belonging to wood-rotting Basidiomycetes are able to grow on and to solubilize different insoluble oxides in solid media. Twenty-eight strains of white rot fungi were checked for their growth on oxide-amended media (ZnO, CaO, Cu2O). All strains displayed growth on Zn-amended plates but to a different extent, and Cu2O-amended plates turned out to be the most toxic oxide. Most of the tested strains solubilized oxalates and produced noticeable clear zones under the mycelium. These clear zones were tested for the presence of organic acids, the level of which was clearly elevated upon exposure of fungal strains to insoluble oxides. We determined the presence of oxalic, malic, and formic acids, with oxalic acid the predominant one.     

Yield of submerged paddy and uptake of Zn,P and N as affected by liming and Zn fertilizers

The effects of CaCO₃, Zn sources and levels on the yield of submerged paddy and uptake of Zn, P and N to paddy were studied in green-house at Haryana Agricultural University, Hissar. Powdered CaCO₃ was mixed at 0,4 and 8 per cent and Zn was added at 0,5 and 10 ppm through ZnSO₄.7H₂O, ZnO and Zn EDTA separately. Dry weight at tillering and heading and grain and straw at maturity decreased significantly with 4 and 8 per cent CaCO₃ in comparison to the control. Increasing Zn application increased the dry weight and grain yield. Zn EDTA gave highest yield of paddy followed by ZnSO₄.7H₂O and ZnO.Increasing the application of CaCO₃ from 0–8 per cent decreased the concentration and uptake of Zn and increasing Zn application from 0–10 ppm increased concentration and uptake of Zn in paddy at tillering, heading and maturity. Zn EDTA gave the highest concentration and uptake of Zn followed by ZnSO₄.7H₂O and ZnO. There was interaction between Zn sources and CaCO₃.The concentration and uptake of N and P in paddy dry matter at tillering and heading and straw and grain at maturity decreased as compared to control with increasing CaCO₃ addition. The concentration and uptake of N increased and that of P decreased in paddy dry matter straw and grain with increasing Zn application. The highest concentration of N was observed with ZnO, followed by ZnSO₄.7H₂O and Zn EDTA. But highest uptake of N was observed with Zn EDTA followed by ZnSO₄.7H₂O and ZnO. As regards concentration and uptake of P, it was highest with ZnO followed by ZnSO₄.7H₂O and Zn EDTA.     

Oxalic acid extraction as a posttreatment to increase the brightness of kraft pulps bleached by white-rot fungi

Pulp brightness gains obtained by fungal biobleaching are often decreased by dark MnO₂ deposits which are formed by the biologically-mediated oxidation of Mn(II). Oxalic acid extraction of O₂-delignified kraft pulps bleached by several white-rot fungi was found to increase pulp brightness by up to 9.7 ISO points due to MnO₂ dissolution. These results indicate that pulp extraction with oxalic acid can be used in order to accurately assess the net brightness gains achieved by fungal biobleaching.     

Rapid,controllable, one‐pot and room‐temperature aqueous synthesis of ZnO:Cu nanoparticles by pulsed UV laser and its application for photocatalytic degradation of methyl orange

Zinc oxide (ZnO) and ZnO:Cu nanoparticles (NPs) were synthesized using a rapid, controllable, one‐pot and room‐temperature pulsed UV‐laser assisted method. UV‐laser irradiation was used as an effective energy source in order to gain better control over the NPs size and morphology in aqueous media. Parameters effective in laser assisted synthesis of NPs such as irradiation time and laser shot repetition rate were optimized. Photoluminescence (PL) spectra of ZnO NPs showed a broad emission with two trap state peaks located at 442 and 485 nm related to electronic transition from zinc interstitial level (I_Zn) to zinc vacancy level (V_Zn) and electronic transition from conduction band to the oxygen vacancy level (V_O), respectively. For ZnO:Cu NPs, trap state emissions disappeared completely and a copper (Cu)‐related emission appeared. PL intensity of Cu‐related emission increased with the increase in concentration of Cu²⁺, so that for molar ratio of Cu:Zn 2%, optimal value of PL intensity was obtained. The photocatalytic activity of Cu‐doped ZnO revealed 50 and 100% increasement than that of undoped NPs under UV and visible irradiation, respectively. The enhanced photocatalytic activity could be attributed to smaller crystal size, as well as creation of impurity acceptor levels (T₂) inside the ZnO energy band gap.     

Induction,purification, and characterization of a thermo and pH stable laccase from Abortiporus biennis J2 and its application on the clarification of litchi juice

A fungus J2 producing laccase with high yield was screened in soils and identified as Abortiporus biennis. The production of laccase was induced by 0.1 mM Cu²⁺, 0.1 mM tannic acid, and 0.5 M ethanol. The laccase from Abortiporus biennis J2 was purified to electrophoretic homogeneity by a couple of steps. The N-terminal amino acid sequence of the enzyme was AIGPTADLNISNADI. The properties of the purified laccase were investigated. The result showed the laccase from Abortiporus biennis J2 is a thermo and pH stable enzyme. The laccase activity was inhibited by Hg²⁺, Cd²⁺, Fe²⁺, Ag⁺, Cu²⁺, and Zn²⁺, while promoted by Mg²⁺, Mn²⁺ at 10 mM level. Purified laccase was used to the clarification of litchi juice. After treatment with this laccase, the phenolic content of litchi juice had been found to be greatly reduced along with an increase in the clarity of the juice. The result indicated the potential of this laccase for application in juice procession.     

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn_1-xMg_xO thin films onto p-type thermally oxidized Cu₂O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu₂O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu₂O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu₂O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu₂O interface. Optimization of AP-SALD conditions as well as keeping Cu₂O away from air and moisture in order to minimize Cu₂O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn_1-xMg_xO/Cu₂O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu₂O-based photovoltaics.     

Species-specific Cd-stress Response in the White Rot Basidiomycetes Abortiporus biennis and Cerrena unicolor

The effect of cadmium (Cd) on fungal growth, Cd bioaccumulation and biosorption, and on the formation of potential heavy metal response indicators such as thiols, oxalate, and laccase was investigated in the white rot fungi Cerrena unicolor andAbortiporus biennis. Only the highest Cd concentration employed (200 μM) inhibited growth of C. unicolor, whereas already lower Cd concentrations caused decreasing mycelia dry weights in A. biennis. Cd biosorption onto the mycelial surface was the predominant Cd sequestration mechanism in C. unicolor. Surface-bound and bioaccumulated Cd concentrations were essentially in the same range in A. biennis, leading to considerably higher intracellular Cd concentrations in A. biennis than in C. unicolor. Oxalate and laccase were produced by both of the fungal strains and their extracellular levels were elevated upon Cd exposure. Oxalate concentrations and laccase titres were considerably higher in C. unicolor than in A. biennis. Both fungi responded to increasing Cd concentrations by increasing intracellular amounts of thiol compounds (cysteine, γ-glutamylcysteine, glutathione in both its reduced and oxidized form) but Cd application increased the amounts of thiols to a higher extend in A. biennis. Taken together, these species-specific responses towards Cd suggest that C. unicolor possesses a more efficient system than A. biennis to keep intracellular Cd concentrations low.     

A role for oxalic acid generation in ozone‐induced signallization in Arabidopis cells

Ozone (O₃) is an air pollutant with an impact increasingly important in our industrialized world. It affects human health and productivity in various crops. We provide the evidences that treatment of Arabidopsis thaliana with O₃ results in ascorbate‐derived oxalic acid production. Using cultured cells of A. thaliana as a model, here we further showed that oxalic acid induces activation of anion channels that trigger depolarization of the cell, increase in cytosolic Ca²⁺ concentration, generation of reactive oxygen species and cell death. We confirmed that O₃ reacts with ascorbate in the culture, thus resulting in production of oxalic acid and this could be part of the O₃‐induced signalling pathways that trigger programmed cell death.     

In vitro antimicrobial effect of metallic nanoparticles on phytopathogenic strains of crop plants

In this research, the in vitro antimicrobial effect of zinc oxide (ZnO), copper oxide (CuO) and iron oxide (Fe₂O₃) nanoparticles (NPs)—with average sizes of 20, 46 and 30 nm, respectively—on the root rot disease caused by the fungus Fusarium oxysporum and on blight disease caused by the fungus Alternaria solani were studied. Also, bacterial diseases caused by Clavibacter michiganensis and Pseudomonas syringae that infects a wide range of plant species were assessed. Different concentrations of NPs (0, 100, 250, 500, 700 and 1,000 mg/L) were prepared on PDA agar or King's B medium in a complete randomized design with four replicates. According to the results, ZnO NPs exhibited an outstanding inhibitory effect against fungi and bacteria strains. The above results were associated with the smaller particle size. Fungi strains showed a differential sensitivity depending on the kind of NPs used. A. solani showed the highest sensitivity to ZnO NPs at 1,000 mg/L (99%), followed by CuO NPs at the same dose (95%). Fe₂O₃ NPs at all evaluated doses had no inhibitory effects on the mycelia growth of this strain, although F. oxysporum revealed greater effectiveness of the CuO NPs (96%) compared with ZnO NPs since it only inhibited 91% of the mycelial growth. The antibacterial activity was studied through optical density. C. michiganensis was found to be more sensitive to ZnO NPs because a lesser dose (700 mg/L) was required to reduce the bacterial growth (90%); in comparison, P. syringae required a dose of 1,000 mg/L to inhibit its growth (67%). CuO NPs displayed the smallest growth inhibition against the bacteria strains analysed. The antimicrobial effect of the metallic NPs that were assayed increased with higher doses.     

Accessing the Two‐Electron Charge Storage Capacity of MnO2 in Mild Aqueous Electrolytes

Rechargeable batteries based on MnO₂ cathodes, able to operate in mild aqueous electrolytes, have attracted attention due to their appealing features for the design of low‐cost stationary energy storage devices. However, the charge/discharge mechanism of MnO₂ in such media is still a matter of debate. Here, an in‐depth quantitative spectroelectrochemical analysis of MnO₂ thin‐films provides a set of unrivaled mechanistic insights. A major finding is that charge storage occurs through the reversible two‐electron faradaic conversion of MnO₂ into Mn²⁺ in the presence of a wide range of weak Brønsted acids, including the [Zn(H₂O)₆]²⁺ or [Mn(H₂O)₆]²⁺ complexes present in aqueous Zn/MnO₂ batteries. Furthermore, it is shown that buffered electrolytes loaded with Mn²⁺ are ideal to achieve highly reversible conversion of MnO₂ with both high gravimetric capacity and remarkably stable charging/discharging potentials. In the most favorable case, a record gravimetric capacity of 450 mA·h·g^?1 is obtained at a high rate of 1.6 A·g^?1, with a Coulombic efficiency close to 100% and a MnO₂ utilization of 84%. Overall, the present results challenge the common view on MnO₂ the charge storage mechanism in mild aqueous electrolytes and underline the benefit of buffered electrolytes for high‐performance rechargeable aqueous batteries.     

Structures and electronic properties of CumConO2(m + n = 2–7) clusters

A theoretical study was carried out of Cu_mCo_nO₂(2?≤?m?+?n?≤?7) clusters using density functional method. O₂ molecules are adsorbed at top sites. After adsorption, O₂ molecules are activated. The Δ₂ E value of CuCo₃O₂ cluster is obviously the smallest, indicating that its thermodynamic stability is the worst. While Cu₆CoO₂ displays stronger chemical stability. Charge transfer from Cu–Co to anti-bonding orbital of O₂, which leads to O–O getting longer. The Mulliken charge population and PDOS analysis are also discussed.     

Assessing in vitro efficacy of certain fungicides to control Sclerotinia sclerotiorum in peanut

The fungal pathogen Sclerotinia sclerotiorum is responsible for Sclerotinia blight in several crops around the world, including peanut. This study was conducted under laboratory conditions to determine the effects of four registered fungicides, Propulse?, Fontelis^®, Omega^® and Endura^® on mycelial growth and pigmentation, as well as sclerotia and oxalic acid production on a growth medium modified with a fungicide and on the pathogenicity of S. sclerotiorum on leaflets detached from Valencia peanut. Propulse, Omega and Fontelis inhibited mycelial growth of S. sclerotiorum, while, mycelial growth on a modified support with Endura was similar to the control treatment. All fungicides, except Endura, inhibited the production of oxalic acid. Pigmentation of the mycelium was observed in both the control and endura treatments. Sclerotia production was observed only in the control treatment. With the exception of Endura, all fungicides were effective in controlling the development of lesions on Valencia peanut leaflets.