Low-Toxicity Self-Photosensitized Biohybrid Systems for Enhanced Light-Driven H2 Production.

Nanoparticles (NPs) represent a potential optoelectronic source capable of significantly boosting hydrogen production; however, their inevitable cytotoxicity may lead to oxidative damage of bacterial cell membranes. In this study, we employed non-photosynthetic Escherichia coli K-12 as a model organism and utilized self-assembled cadmium sulfide (CdS) nanoparticles to construct a low-toxicity and hydrogen-production-enhancing self-photosensitive hybrid system. To mitigate the cytotoxicity of CdS NPs and synthesize biocompatible CdS NPs on the cell surface, we employed engineered E. coli (efeB/OE) for bioremediation, achieving this goal through the overexpression of the peroxidase enzyme (EfeB). A comparative analysis with E. coli-CdS revealed a significant downregulation of genes encoding oxidative stress proteins in efeB/OE-CdS post-irradiation. Atomic force microscopy (AFM) confirmed the stability of bacterial cell membranes. Due to the enhanced stability of the cell membrane, the hydrogen yield of the efeB/OE-CdS system increased by 1.3 times compared to the control, accompanied by a 49.1% reduction in malondialdehyde (MDA) content. This study proposes an effective strategy to alleviate the toxicity of mixed biological nanoparticle systems and efficiently harness optoelectronic electrons, thereby achieving higher hydrogen production in bioremediation.

Fe3 O4 nanozyme coating enhances light-driven biohydrogen production in self-photosensitized Shewanella oneidensis-CdS hybrid systems.

Solar-driven biohybrid systems that produce chemical energy are a valuable objective in ongoing research. However, reactive oxygen species (ROS) that accompany nanoparticle production under light radiation severely affect the efficiency of biohybrid systems. In this study, we successfully constructed a two-hybrid system, Shewanella oneidensis-CdS and S. oneidensis-CdS@Fe3 O4 , in a simple, economical, and gentle manner. With the Fe3 O4 coating, ROS were considerably eliminated; the hydroxyl radical, superoxide radical, and hydrogen peroxide contents were reduced by 66.7%, 65.4%, and 72%, respectively, during light-driven S. oneidensis-CdS hydrogen production. S. oneidensis-CdS@Fe3 O4 showed a 2.6-fold higher hydrogen production (70 h) than S. oneidensis-CdS. Moreover, the S. oneidensis-CdS system produced an additional 367.8 µmol g-dcw-1 (70 h) of hydrogen compared with S. oneidensis during irradiation. The apparent quantum efficiencies of S. oneidensis-CdS and S. oneidensis-CdS@Fe3 O4 were 6.2% and 11.5%, respectively, exceeding values previously reported. In conclusion, a stable nanozyme coating effectively inhibited the cytotoxicity of CdS nanoparticles, providing an excellent production environment for bacteria. This study provides a rational strategy for protecting biohybrid systems from ROS toxicity and contributes to more efficient solar energy conversion in the future.

Cobalt-doped double-layer α-Fe2O3 nanorod arrays for enhanced photoelectrochemical reduction of Cr(VI).

Element doping is an important method for improving the performance levels of photoelectrochemical (PEC) cells. Nevertheless, to date, the PEC conversion efficiency and photocurrent characteristics of the available photoanodes remain very low. In this study, cobalt (Co) was selectively doped into the bottom and/or top layers of double-layered α-Fe2O3 nanorod arrays grown on conductive transparent substrates (F:SnO2, FTO) via a two-step hydrothermal method; this process was performed to enhance the charge transfer ability and thus significantly improve the PEC performance. The light response capabilities of all α-Fe2O3 films were evaluated by an electrochemical workstation under dark or visible light irradiation conditions. The sample of Co doped in the bottom layer exhibited a high photoelectrochemical performance, achieving a current density of 1.37 mA/cm2 at + 1.0 V versus saturated calomel electrode (SCE); additionally, the sample exhibited a photoelectric synergistic ability to reduce Cr(VI) in an aqueous solution, with 84.85% reduction in 180 min. Under the influence of the electric field inside the double-layer electrode, the photoexcited electrons and holes are transferred to the surfaces of the FTO substrate and the photoanode, increasing the current density and enhancing Cr(VI) reduction. The results of this study offer an alternative approach for designing novel photoanodes with improved PEC performance levels by engineering the electron density distribution and band structure for efficient carrier separation; the results may provide new solutions in heavy metal reduction and contaminant degradation projects.

Light-driven biodegradation of azo dyes by Shewanella decolorationis-CdS biohybrid in wastewater lacking electron donors.

The lack of electron donors prevents the effective degradation of azo dyes by bacteria, which severely limits the practical application of conventional biological treatment. Herein, we innovatively designed a bio-photoelectric reduction degradation system composed of CdS and Shewanella decolorationis, which could effectively degrade amaranth in anaerobic conditions driven by light when electron donors were unavailable. Compared with bare S. decolorationis and S. decolorationis (heat-killed)-CdS biohybrid, S. decolorationis-CdS biohybrid had 39.36-fold and 3.82-fold higher first-order kinetic constants, respectively. The morphology, particle size, elemental composition, crystalline type, photovoltaic properties, and band structure of the nanoparticles synthesized by S. decolorationis were carefully examined and analyzed. Light-driven biodegradation experiments showed that amaranth was degraded by the synergy of CdS and S. decolorationis. Reductive degradation of amaranth by electrons was demonstrated by electron and hole trapping. The effect of potential coexisting contaminants, which might serve as hole scavengers, on the degradation of amaranth was evaluated. Membrane protein inhibition experiments also suggested that NADH dehydrogenase, menaquinone, and cytochrome P450 played an important role in electron transfer between CdS and Shewanella decolorationis. The cyclic conversion of NAD+/NADH was probably the most critical rate-limiting step. Electrochemical measurements suggested that faster electron transfer might facilitate the degradation of amaranth. Our findings might contribute to the degradation of azo dyes in wastewater lacking electron donors and deepen our recognition of the microbe-material interface. KEY POINTS: • A BPRDS was constructed with Shewanella decolorationis and CdS. • Amaranth was effectively degraded by BPRDS in anaerobic conditions driven by light. • NDH, MQ, and CYP450 were involved in electron transfer.

The Biodegradation of Indigo Carmine by Bacillus safensis HL3 Spore and Toxicity Analysis of the Degradation Products.

The aims of this article were to investigate Bacillus safensis HL3 spore for its capacity to degrade and detoxify indigo carmine and to provide an effective biological agent for the treatment of isatin dye wastewater. Bacillus safensis HL3 spore was found to decolorize indigo carmine by 97% in the presence of acetosyringone within 2 h. Significantly increased activities of spore laccase, intracellular tyrosinase, and lignin peroxidase upon exposure to indigo carmine were observed. The results of RT-qPCR also showed that the expression of laccase gene was significantly increased. The spore has the ability to degrade indigo carmine through oxidization. Furthermore, the pathway by which indigo carmine is degraded was investigated using liquid chromatography-mass spectrometry analysis to identify the biodegradation products. A detailed pathway of indigo carmine degradation by bacterial spores was proposed for the first time. Toxicity tests indicated that the biodegradation products of indigo carmine are non-toxic to Nicotiana tabacum seeds and are less hazardous to human erythrocytes than the original dye. Indigo carmine is a typical recalcitrant dye and severely jeopardizes human health. The results demonstrate the utility of the spore from Bacillus safensis HL3 for the degradation of indigo carmine and simultaneous reduction of its toxicity.

Photocatalytic performance of an α-Fe2O3 electrode and its effects on the growth and metabolism of Citrobacter freundii.

Electronic exchanges occur between semiconductor minerals and microorganisms. However, researchers have focused on the photocatalytic degradation of pollutants by semiconductor minerals, and there is a limited amount of studies on semiconductor photogenerated electrons that influence the growth and energetic mechanisms of bacteria. Bioelectrochemical systems (BES) are important new bioengineering technologies for investigating the mechanisms by which bacteria absorb electrons. In this work, we built a BES that used α-Fe2O3 nanorods as a photoanode and Citrobacter freundii as bio-cathode bacteria to explore the effect of photoelectrons on C. freundii growth and metabolism. The photoanode was prepared by a hydrothermal synthesis method. As confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the photoanode was made of α-Fe2O3. Corresponding scanning electron microscope (SEM) images showed that α-Fe2O3 nanorod arrays formed with a diameter of 50 nm, and the band gap was 2.03 eV, as indicated by UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The C. freundii growth metabolism changed significantly because of photoelectrons; under light conditions, the growth rate of C. freundii significantly accelerated, and as inferred from the three-dimensional fluorescence spectrum, the protein, humic acid, and NADH concentrations were significantly higher at 72 h. According to the changes in the organic acid content, photoelectrons participated in the reductive tricarboxylic acid cycle (rTCA) to enhance growth and metabolism. The results of the study have broad implications for advancing fields that study the effects of semiconductor minerals on electroactive microorganisms and the semiconductor-photoelectronic transport mechanisms of electroautotrophic microorganisms. KEY POINTS: • For the first time, A BES was built that used α-Fe2O3 nanorods as a photoanode and C. freundii as a bio-cathode bacteria. • Photoelectrons produced by α-Fe2O3 photoelectrode promote the growth of C. freundii. • Effects of photoelectrons on C. freundii metabolism were conjectured by the changes of organic acids and NADH.

[Effect of exogenous CdS nanoparticle on the growth of Escherichia coli].

Semiconductor nanoparticles generate photoelectrons and photo-induced holes under light excitation, and thus may influence the growth of microbial cells. The highly oxidative holes may severely damage the cells, while the photoelectrons may promote microbial metabolism. In this study, we evaluated the effect of exogenous cadmium sulfide (CdS) nanoparticles on bacterial growth using OD600 and colony forming unit (CFU) as indicators. The oxidase activities, the concentration of pyruvate and malondialdehyde, and the expression of relevant genes assessed by real-time fluorescent quantitative PCR were analyzed to investigate the effect of excited CdS on cellular metabolism. The results showed that the OD600 and pyruvate accumulation of E. coli increased by 32.4% and 34.6%, respectively, under light conditions. Moreover, the relative expression level of the division protein gene ftsZ was increased more than 50%, and the tricarboxylic acid cycle pathway gene icdA and gltA increased by 86% and 103%, respectively. The results indicated that photoelectrons could be used by microorganisms, resulting in promoted growth and metabolism. This study gives a deep insight into the interaction between nanoparticles and bacteria.

Fabrication and characterization of CdS nanowires templated in tobacco mosaic virus with improved photocatalytic ability.

Using a virus as a template to synthesize nanomaterial is a simple, green, and controllable method to acquire unique structure nanoparticles. In this study, CdS nanowires were synthesized using the tobacco mosaic virus (TMV) as a template and for deposition in the inner center channel of TMV. TMV/CdS was successfully characterized, with the results showing a diameter of 4.0 nm, a cubic-phase composition, and strong fluorescence emission peaks, with an absorption edge of 566 nm and bandgap energy of 2.28 eV. The bandgap energy is narrower than that of template-free CdS. Furthermore, TMV/CdS exhibited an increased transient photocurrent, which was attributed to the effective separation of electron-hole pairs. The photoactivities of TMV/CdS and template-free CdS were tested; the results showed that the TMV/CdS had a better performance in methylene blue (MB) photodegradation, indicating that the photoactivity of TMV/CdS was higher than that of the template-free CdS. Further research on TMV/CdS regarding the photocatalytic mechanism showed that O2•- and •OH were the major species involved in photocatalysis, rather than holes (h+). Therefore, TMV/CdS might have applications as a novel visible-light-responsive photocatalyst. KEY POINTS: • CdS nanowires were firstly synthesized in the inner center channel of TMV • TMV/CdS presented higher photocatalytic efficiency compared with template-free CdS • The O2•- and •OH were responsible for the photocatalytic reaction of TMV/CdS.

The cytotoxicity of endogenous CdS and Cd2+ ions during CdS NPs biosynthesis.

In the present study, cadmium-based nanoparticles (NPs) were biosynthesized by incubating their precursor salts with E. coli CD-2. Transmission electron microscopy (TEM) revealed the morphology of the NPs and confirmed that the NPs were formed via an intracellular growth. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) determined the elemental composition of the NPs and identified the NPs as CdS. The contents of extracellular Cd2+, intracellular Cd2+ and intracellular CdS NPs were determined during the whole CdS biosynthetic process. The results demonstrated that the contents of Cd2+ and CdS NPs changed during the biosynthetic process. The colony-forming capability test showed that strain CD-2 could maintain its growth during CdS biosynthesis. Protein oxidation levels confirmed that the E. coli cells faced oxidative stress induced both by Cd2+ and CdS. Both Cd2+ and CdS NPs affected the cellular antioxidative system by upregulating related gene expression. However, different pathways might be involved to eliminate ROS induced by Cd2+ ions or CdS NPs, respectively. The expression levels of ef-tu, ftsZ, mutS and dnaK were enhanced together with CdS accumulation, indicating that the cells had to overexpress certain related genes to respond to the NPs-induced stress.

TMT-based quantitative proteomic analysis of antitumor mechanism of Sporisorium reilianum polysaccharide WM-NP-60 against HCT116 cells.

Sporisorium reilianum is an active edible and medicinal phytopathogenic fungus. Our study indicated that the S. reilianum polysaccharide WM-NP-60 could inhibit the growth of HCT116 cells in a dose-dependent manner. In addition, WM-NP-60 could trigger the cell cycle of HCT116 arrest at the G1 phase and induce its apoptosis. In order to explore the anti-tumor mechanism of WM-NP-60, TMT-based quantitative proteomic analysis was used. Results indicated that 369 differentially expressed proteins including 240 up-regulated and 129 down-regulated proteins in WM-NP-60 treated HCT116 cells compared with normal HCT116 cells. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that 192 pathways were enriched containing 15 metabolic pathways with significant difference (P < 0.05). The levels of mRNA and protein up-regulated TGFßR1, P107, DP1 and down-regulated THBS1 related to TGF-ß signaling pathway were verified with qRT-PCR and Western Blot (WB). These findings will provide theoretical basis for the important role of fungal polysaccharides in the field of tumor treatment.

Effect of quinoid redox mediators during azo dye decolorization by anaerobic sludge: Considering the catalyzing mechanism and the methane production.

The effects of quinoid compounds on azo dyes decolorization were studied. Compared with other quinones, menadione was the most effective at aiding azo dye decolorization. Sodium formate was a suitable carbon source for the anaerobic decolorization system. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis indicated that the microbial structure changed in response to varying carbon sources. Phylogenetic analysis showed that the anaerobic sludge was consisted mainly of nine genera. The mechanism studies showed that the biotransformation of menadione to its hydroquinone form was the rate-limiting step in the dye decolorization process. Moreover, study of the electron transfer mechanism of quinone-mediated reduction showed that azo dye decolorization is not a specific reaction. The NADH chain was involved in the decolorization process. The methane production test indicated that azo dyes had an inhibitory effect on methane production. However, supplementation with a redox mediator could recover the inhibited methanogenesis. High-throughput sequencing analysis revealed that the methanogenic archaeal community was altered in the anaerobic sludge with or without azo dyes and the redox mediator.

In vitro antifungal activity and possible mechanisms of action of chelerythrine.

Chelerythrine (CHE) possesses broad pharmacological activities. In this study, the extract of Chelidonium majus L. were characterized by high performance liquid chromatography (HPLC), infrared radiation (IR) spectroscopy and nuclear magnetic resonance (NMR). It was proved that the extract was CHE. The antifungal activity of CHE against five fungal pathogens of rice was researched in vitro, revealing that CHE inhibited Ustilaginoidea virens (U. virens) and Cochliobolus miyabeanus (C. miyabeanus) with 50% effective concentrations (EC50) of 6.53 × 10-3 mg/mL and 5.62 × 10-3 mg/mL, respectively. When the concentration of CHE was 7.5 × 10-3 mg/mL, the inhibition rate of U. virens reached 56.1%. Moreover, CHE (4 × 10-3 mg/mL) exhibited the greatest efficacy in inhibiting spore of U. virens growth with an inhibition rate as high as 86.7%. CHE displayed the best inhibitory activity against U. virens at the concentration of 7.5 × 10-3 mg/mL, compared with the other two isoquinoline alkaloids and commercial fungicide validamycin. After treating U. virens mycelia with CHE, twisted and atrophied mycelia were observed by optical microscopy. SEM results demonstrated narrow and locally fractured mycelium. TEM observations showed that the cell wall had become thin and broken, and most organelles were difficult to recognize. Furthermore, membrane of mycelia was destroyed and reactive oxygen species (ROS) of spores was accumulated, which induced apoptosis of pathogenic fungi. From these results, our understanding of the mechanisms of antifungal activity of CHE against U. virens was enriched and this research is relevant for developing novel pesticides.

De Novo Iron Oxide Hydroxide, Ferrihydrite Produced by Comamonas testosteroni Exhibiting Intrinsic Peroxidase-Like Activity and Their Analytical Applications.

Natural enzyme mimics have attracted considerable attention due to leakage of enzymes and their easy denaturation during their storage and immobilization procedure. Here in this study, for the first time, a new iron oxide hydroxide, ferrihydrite - Fe1.44O0.32 (OH) 3.68 magnetic nanoparticles were synthesized by bacterial strain named Comamonas testosteroni. The characterization of the produced magnetic nanoparticles was confirmed by transmission electron microscopy (TEM), Fourier-transform spectroscopy (FTIR), X-ray diffraction (XRD), and magnetization hysteresis loops. Further, these extracted nanoparticles were proven to have biogenic magnetic behavior and to exhibit enhanced peroxidase-like activity. It is capable of catalyzing the oxidation of 3, 3', 5, 5'-Tetramethylbenzidine (TMB) by H2O2 to produce blue color (typical color reactions). Catalysis was examined to follow Michaelis-Menton kinetics and the good affinity to both H2O2 and TMB. The K m value of the Fe1.44O0.32 (OH) 3.68 with H2O2 and TMB as the substrate was 0.0775 and 0.0155 mM, respectively, which were lower than that of the natural enzyme (HRP). Experiments of electron spin resonance (ESR) spectroscopy proved that the BMNPs could catalyze H2O2 to produce hydroxyl radicals. As a new peroxidase mimetic, the BMNPs were exhibited to offer a simple, sensitive, and selective colorimetric method for determination of H2O2 and glucose and efficiently catalyze the detection of glucose in real blood samples.

Bacterial intracellular nanoparticles exhibiting antioxidant properties and the significance of their formation in ROS detoxification.

Biogenic magnetic nanoparticles (BMNPs) can be formed by numerous microorganisms. However, the significance of their formation and their possible functions have not been explored in detail. To explore a possible function of Fe3 O4 NPs in Burkholderia sp. strain YN01, we investigated their catalytic abilities in the elimination of intracellular reactive oxygen species (ROS). Changes in ROS content under different conditions were assessed and showed that low oxygen and high iron concentrations in the growth medium promoted ROS production. However, the levels of ROS gradually decreased with BMNP formation, suggesting that these particles possess intrinsic superoxide dismutase (SOD)-like activity and catalase (CAT)-like activity, as proven in this study. To ensure that the observed ROS decrease was not due to antioxidase overexpression caused by the oxidative stress response, SOD and CAT were inhibited in vivo to analyse the ROS variation and BMNP yield under microoxic and high-iron conditions respectively. The results demonstrated that the formation of these intracellular iron nanoparticles was required for the efficient scavenging of excess ROS, which was dependent on their antioxidase-like properties. This result reveals a novel physiological function of biogenic intracellular Fe3 O4 nanoparticles.

The Comparative Study on the Rapid Decolorization of Azo, Anthraquinone and Triphenylmethane Dyes by Anaerobic Sludge.

An anaerobic sludge (AS), capable of decolorizing a variety of synthetic dyes, was acclimated and is reported here. The sludge presented a much better dye decolorizing ability than that of different individual strains. A broad spectrum of dyes could be decolorized by the sludge. Continuous decolorization tests showed that the sludge exhibited the ability to decolorize repeated additions of dye. The chemical oxygen demand (COD) removal rate of the dye wastewater reached 52% after 12 h of incubation. Polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) profiles revealed that the microbial community changed as a result of varying initial concentrations of dyes. Phylogenetic analysis indicated that microbial populations in the sludge belonged to the phyla Acidobacteria, Firmicutes, Bacteroidetes, Chloroflexi and Proteobacteria. The degradation products of the three types of dye were identified. For azo dyes, the anaerobic sludge converted Methyl Orange to N,N-dimethylbenzene-1,4-diamine and 4-aminobenzenesulfonic acid; for triphenylmethane dyes, after Malachite Green was decolorized, the analyzed products were found to be a mixture of N,N-dimethylbenzenamine, 3-dimethyl-aminophenol and 4-dimethylaminobenzophenone; for anthraquinone dyes, two products (acetophenone and 2-methylbenzoic acid) were observed after Reactive Blue 19 decolorization. Together, these results suggest that the anaerobic sludge has promising potential for use in the treatment of industrial wastewater containing various types of dyes.

Effect of quinoid redox mediators on the aerobic decolorization of azo dyes by cells and cell extracts from Escherichia coli.

It is widely accepted that the addition of redox mediators increases the decolorization rates of azo dyes by bacterial strains under anaerobic conditions. However, little information exists about whether quinoid redox mediators can enhance the performance of aerobic azo dye decolorization. In the present study, quinone-mediated decolorization of different azo dyes by whole cells and cell extracts from the Escherichia coli strain CD-2 under aerobic conditions were investigated. The results demonstrated that reduction rates of different azo dyes were greatly increased when quinone compounds were used as redox mediators. Compared with menadione, 2-hydroxy-1,4-naphthoquinone (lawsone) was more effective at aiding azo dye degradation and the optimum concentration for lawsone is 0.1 mM. Strain CD-2 and the anthraquinone were co-immobilized by entrapment in different polymeric matrices. The co-immobilized beads exhibited good catalytic activity for azo dye degradation and kept stable during successive repeated experiments. The mechanism of the quinone-mediated reduction showed that although whole cells incubated with quinones could significantly increase the rate of decolorization of azo dyes, the quinone compounds did not directly promote azoreductase activity. According to the survey, this is the first report to confirm that the addition of quinoid redox mediators to bacteria increased decolorization under aerobic conditions.

Biogenic magnetic nanoparticles from Burkholderia sp. YN01 exhibiting intrinsic peroxidase-like activity and their applications.

A novel bacterial strain containing biogenic magnetic nanoparticles (BMNPs) was isolated from the sediments of Songhua River in Harbin, China, and was identified as Burkholderia sp. YN01. Extracted BMNPs from YN01 were characterized as pure face-centered cubic Fe3O4 with an average size of 80 nm through transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The hysteresis parameters of the BMNP samples such as Bc and Bcr and ratios Mrs/Ms were deduced as 35.6 mT, 43.2 mT, and 0.47, respectively, indicating that the BMNPs exhibit a ferromagnetic behavior. This is the first report concerning on biogenic Fe3O4 NPs produced in Burkholderia genus. Significantly, the BMNPs were proved to possess intrinsic peroxidase-like activity that could catalyze the oxidation of peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Kinetic analysis indicates that the catalytic behavior is in accord with typical Michaelis-Menten kinetics and follows ping-pong mechanism. The catalytic constants (K cat) were 6.5 × 10(4) s(-1) and 0.78 × 10(4) s(-1) with H2O2 and TMB as substrate, respectively, which was higher than that of horseradish peroxidase (HRP). Electron spin resonance (ESR) spectroscopy experiments showed that the BMNPs could catalyze H2O2 to produce hydroxyl radicals. The origin of peroxidase-like activity is also associated with their ability to transfer electron between electrode and H2O2 according to an electrochemical study. As a novel peroxidase mimetic, the BMNPs were employed to offer a simple, sensitive, and selective colorimetric method for H2O2 and glucose determination, and the BMNPs could efficiently catalyze the degradation of phenol and Congo red dye.

Decolourization of azo dyes by a newly isolated Klebsiella sp. strain Y3, and effects of various factors on biodegradation.

In this study, we isolated and characterized a new strain of Klebsiella sp. Y3, which was capable of decolourizing azo dyes under anaerobic conditions. The effects of physico-chemical parameters on the Methyl Red degradation by the strain were determined. The results indicated that strain Y3 exhibited a good decolourization ability in the range of pH from 4 to 9, temperature from 30 °C to 42 °C and salinity from 1% to 4%. A broad spectrum of azo dyes with different structures could be decolourized by the strain. The isolate decolourized Methyl Red, Congo Red, Orange I and Methyl Orange by almost 100% (100 mg/L) in 48 h. The culture exhibited an ability to decolourize repeated additions of dye, showing that the strain could be used for multiple cycles of biodegradation. Azo dyes at high concentrations could be tolerated and degraded by Y3. An almost complete mineralization of Methyl Red and Congo Red at the concentration of 800 mg/L was observed within 48 h. The high degradation potential of this bacterium supports its use in the treatment of industrial wastewater containing azo dyes.

Characterisation of a novel white laccase from the deuteromycete fungus Myrothecium verrucaria NF-05 and its decolourisation of dyes.

A novel 'white' laccase was purified from the deuteromycete fungus, Myrothecium verrucaria NF-05, which was a high laccase-producing strain (40.2 U·ml(-1) on the thirteenth day during fermentation). SDS-PAGE and native-PAGE revealed a single band with laccase activity corresponding to a molecular weight of approximately 66 kDa. The enzyme had three copper and one iron atoms per protein molecule determined by ICP-AES. Furthermore, both UV/visible and EPR spectroscopy remained silence, indicating the enzyme a novel laccase with new metal compositions of active centre and spectral properties. The N-terminal amino acid sequence of the purified protein was APQISPQYPM. Together with MALDI-TOF analysis, the protein revealed a high homology of the protein with that from reported M. verrucaria. The highest activity was detected at pH 4.0 and at 30°C. The enzyme activity was significantly enhanced by Na(+), Mn(2+), Cu(2+) and Zn(2+) while inhibited by DTT, NaN(3) and halogen anions. The kinetic constant (Km) showed the enzyme was more affinitive to ABTS than other tested aromatic substrates. Twelve structurally different dyes could be effectively decolourised by the laccase within 10 min. The high production of the strain and novel properties of the laccase suggested its potential for biotechnological applications.

Microbial community structures in mixed bacterial consortia for azo dye treatment under aerobic and anaerobic conditions.

Thirteen pure strains that possessed high methyl red (MR)-decolorizing ability were isolated from dye-contaminated water. Each isolate was identified by 16S rDNA sequencing. The results reveal that all of the isolated strains were facultative anaerobic bacteria. Two novel bacterial consortia (AE and AN), which could decolorize MR under aerobic and anaerobic conditions, respectively, were developed. Azo dye decolorization rate was significantly higher with the use of consortia compared to that with the use of individual strains. Both of the consortia can decolorize different azo dyes effectively in a short time, and tolerate MR with high concentrations. To provide further insight into the microbial diversity of the bacteria consortia under aerobic and anaerobic conditions, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analyses were performed. PCR-DGGE profiles revealed that the microbial community had changed significantly with varying initial concentrations of MR. Phylogenetic analysis indicated that microbial populations in the aerobic compartment belong to Klebsiella, Buttiauxella and Bacillus, whereas Klebsiella, Escherichia, Bacillus and Clostridium were present in the anaerobic compartment. Klebsiella, which was the majority genus in both of the consortia, may play an important role in azo dye removal.