Reduced toxicity of malachite green decolorized by laccase produced from Ganoderma sp. rckk-02 under solid-state fermentation

Exploring fungal-mediated solutions and its molecular mechanistic insights for textile dye decolorization

Decolorization of textile dyes and study of their intermediate compounds is necessary to comprehend the mechanism of dye degradation. In the present study, different fungal mediated solutions were explored to provide an alternative to treat the reactive dyes. Growing biomass of Pleurotus sajor caju showed 83% decolorization (249.99 mg L-1 removal) of Reactive Blue 13 (RB 13) and 63% decolorization (188.83 mg L-1) of Reactive Black 5 (RB 5) at 300 mg L-1 initial concentration on 8 d. Higher laccase activity was positively correlated with increase in decolorization. However, increasing dye concentration has inhibitory effect on fungal biomass due to increase in toxicity. In laccase mediated decolorization, laccase produced from P. sajor caju using carbon rich waste material as substrate showed 89% decolorization (276.36 mg L-1 removal) of RB 13 and 33% decolorization (105.37 mg L-1 removal) of RB 5 at 300 mg L-1 initial dye concentration in 100 min at 30 °C and pH 3.0'. Comparing the two methods, laccase-mediated decolorization shows better decolorization in less time and does not produce sludge. Further, the present work also attempted to study the dye degradation pathway for Reactive blue 13 via laccase mediated process. Fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS) were utilized to identify the degraded products. The GC-MS analysis showed the formation of naphthalene, naphthalene 2-ol, benzene,1-2, dicarboxylic acid, 4, amino, 6,chloro, 1-3-5, triazin-2-ol as the final degraded products after enzymatic degradation of RB 13. These findings provide in-depth study of laccase-mediated textile dye degradation mechanism.

Improved laccase production by Trametes versicolor using Copper-Glycyl-L-Histidyl-L-Lysine as a novel and high-efficient inducer

A highly efficient strategy using Copper-Glycyl-L-Histidyl-L-Lysine (GHK-Cu) as a novel inducer was developed to enhance laccase production by Trametes versicolor. After medium optimization, laccase activity increased by 12.77-fold compared to that without GHK-Cu. The laccase production of 1113.8 U L-1 was obtained by scaling-up culture in 5-L stirring tank. The laccase production induced by CuSO4 was poorer than that of GHK-Cu at the same mole concentration. GHK-Cu could increase the permeability of cell membrane with less damage, and it facilitated the adsorption, accumulation, and utilization of copper by fungal cells, which was beneficial for laccase synthesis. GHK-Cu induced better expression of laccase related genes than that of CuSO4, resulting in higher laccase production. This study provided a useful method for induced production of laccase by applying GHK chelated metal ion as a non-toxic inducer, which reduced the safety risk of laccase broth and provided the potential application of crude laccase in food industry. In addition, GHK can be used as the carrier of different metal ions to enhance the production of other metalloenzymes.

Enrichment of laccase production by Phoma herbarum isolate KU4 under solid-state fermentation by optimizing RSM coefficients using genetic algorithm

The process parameters were optimized to obtain enhanced enzyme activity from the fungus Phoma herbarum isolate KU4 using rice straw and saw dust as substrate under solid-state fermentation using Response surface methodology (RSM). Genetic algorithm was used to validate the RSM for maximum laccase production. Six variables, viz., pH of the media, initial moisture content, copper sulphate concentration, concentration of tannic acid, inoculum concentration and incubation time were found to be effective and optimized for enhanced production. Maximum laccase production was achieved by RSM at pH 5·0 and 86% of initial moisture content of the culture medium, 150 µmol l^-1 of CuSO₄ , 1·5% tannic acid and 0·128 g inoculum g^-1 dry substrate inoculum size on the fourth day of fermentation. The highest laccase activity was observed as 79 008 U g^-1 , which is approximately sixfold enhanced production compared to the unoptimized condition (12 085·26 U g^-1 ).

Laccase production by Trametes versicolor in solid-state fermentation using tea residues as substrate and its application in dye decolorization

An efficient valorization of tea residues into value-added product was developed by Trametes versicolor in solid-state fermentation (SSF). The laccase production of 25.7 U/g dry substrate was obtained by optimizing culture medium and condition, resulting in a 4.0-fold increase compared to that of 6.4 U/g dry substrate under unoptimized condition. During the 7-day cultivation under SSF, 44.7%, 12.2% and 9.8% degradation occurred for lignin, hemicellulose and cellulose in tea residues, respectively. Laccase production reached 31.2 U/g dry substrate by the scaling-up culture in shallow tray system. The dry fermented tea residues were directly used as crude enzyme in the decolorization of malachite green. It possessed a decolorization rate of more than 95% within 120 min and remained 81.3% of decolorization capacity after 6 cycles. The present study provided a useful strategy for low-cost laccase production by SSF and it exhibited great potential for the application in dye decolorization.

Removal of dyes by immobilization of Trametes versicolor in a solid-state micro-fermentation system

A novel bioreactor system (low cost and easily scaled-up) is presented for dye decolorization applying filamentous fungi. In this two-phase bioreactor, dyes were decolorized at 28°C in a first phase by immobilized fungi in spherical cartridges prepared with a high-density plastic polyethylene mesh and filled with wheat bran as substrate for growth. In a second phase the capacity of the ligninolytic enzymes (laccase and Mn-peroxidase) present in the extracellular extracts from the solid residues was exploited for decolorization at 50°C. Each sphere behaved as a small-scale bioreactor for cell-culture. This system allowed the decoupling of growth (sterile condition) and decolorization (non-sterile condition) stages. The ability to decolorize the azo dye xylidine and the triphenylmethane Malachite Green by two Argentinean strains of Trametes versicolor was evaluated. The highest decolorization rates were displayed by T. versicolor BAFC 2234. When both dyes were applied together in the bioreactor, after a first phase (100min) 73.5% of Malachite Green and 40% of xylidine decolorization was attained, while at the end of the second phase (240min) a 97% and 52% decolorization was observed. Laccase activity was detected in the decolorized solution, but no Mn-peroxidase activity. The easy change of the cartridges allows the continuous use of the bioreactor in the non-sterile decolorization of dye-containing effluents.

Fungal Laccase Production from Lignocellulosic Agricultural Wastes by Solid-State Fermentation: A Review

Laccases are copper-containing oxidase enzymes found in many fungi. They have received increasing research attention because of their broad substrate specificity and applicability in industrial processes, such as pulp delignification, textile bleaching, phenolic removal, and biosensors. In comparison with traditional submerged fermentation (SF), solid-state fermentation (SSF) is a simpler technique for laccase production and has many advantages, including higher productivity, efficiency, and enzyme stability as well as reduced production costs and environmental pollution. Here, we review recent advances in laccase production technology, with focus on the following areas: (i) Characteristics and advantages of lignocellulosic agricultural wastes used as SSF substrates of laccase production, including detailed suggestions for the selection of lignocellulosic agricultural wastes; (ii) Comparison of fungal laccase production from lignocellulosic substrates by either SSF or SF; (iii) Fungal performance and strain screening in laccase production from lignocellulosic agricultural wastes by SSF; (iv) Applications of laccase production under SSF; and (v) Suggestions and avenues for future studies of laccase production by fungal SSF with lignocellulosic materials and its applications.

Identification and evaluation of bioremediation potential of laccase isoforms produced by Cyathus bulleri on wheat bran

Multiplicity in laccases among lignin degrading fungal species is of interest as it confers the ability to degrade several types of lignocellulosics. The combination of laccases produced on such substrates could be beneficial for treatment of complex aromatics, including dyes. In this study, we report on production of high units (679.6Ug^-1 substrate) of laccase on solid wheat bran (WB) by Cyathus bulleri. Laccase, purified from the culture filtrates of WB grown fungus, was effective for oxidation of veratryl alcohol, Reactive blue 21 and textile effluent without assistance of externally added mediators. De novo sequencing of the 'purified' laccase lead to identification of several peptides that originated from different laccase genes. Transcriptome analysis of the fungus, cultivated on WB, confirmed presence of 8 isozymes, that were re-amplified and sequenced from the cDNA prepared from WB grown fungus. The 8 isozymes were grouped into 3 classes, based on their sequence relationship with other basidiomycete laccases. The isoforms produced on WB decolorized (by ∼57%) and degraded textile effluent far more effectively, compared to laccase obtained from Basal salt cultivated fungus. The decolorization and degradation was also accompanied by more than 95% reduction in phytotoxicity.

Effects of wheat straw solid contents in fermentation media on utilization of soluble/insoluble nutrient, fungal growth and laccase production

The objective of the work was to study the effect of agri-residue solid contents (2-20% w v-1) in fermentation medium on fungal growth, soluble and insoluble nutrient consumption and laccase production. Fungal strain Ganoderma lucidium and wheat straw substrate was screened for maximum laccase production. At low solid content submerged fermentation (SmF), fungus utilized mainly soluble nutrient and was unable to access the insoluble nutrient in media due to lack of contact with solid. At high solid content solid-state fermentation (SF), fungi grew on solid surface with dense and thin hyphae, utilized mainly insoluble nutrient. At medium solid content (8% w v-1) semi-solid fermentation (sSF), fungi grew on solid substrates with network of thick intercrossed hyphae, utilized both soluble and insoluble nutrients optimally resulting in highest fungal growth and laccase activity (~ 3.5 folds than in SmF and ~ 2.5 folds than in SF). Importance of soluble and insoluble nutrients was also established after isolation of their individual effects. Morphology of fungal growth (SEM), composition, thermal analysis (TGA/DTG) of substrates confirmed the results. sSF showed potential for the production of enzymes through utilization of agricultural residues as substrate.

Purification and immobilization of laccase from Trichoderma harzianum strain HZN10 and its application in dye decolorization

In this study we report the purification of laccase produced by Trichoderma harzianum strain HZN10 (using wheat bran under solid state fermentation) and its application in decolorization of synthetic dyes. Extracellular laccase was purified to homogeneity by DEAE-Sepharose and Sephadex G-100 chromatography with specific activity of 162.5 U/mg and 25-fold purification. Purified laccase was immobilized in various entrapments like calcium alginate, copper alginate, calcium alginate–chitosan beads and sol–gel matrix. Optimization results revealed that the laccase immobilized in sol–gel was optimally active in wide pH range (4.0–7.0) and thermo-stable (50–70 °C) than free enzyme which was optimum at 50 °C and pH 6.0. Kinetic analysis showed K_m of 0.5 mM and 2.0 mM and V_max of 285 U/mg and 500 U/mg by free laccase and sol–gel immobilized laccase respectively with 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) [ABTS] substrate. Free and immobilized laccase was employed for decolorization of three different synthetic dyes (malachite green, methylene blue and congo red). High performance liquid chromatography (HPLC) analysis results revealed that approximately 100% of malachite green, 90% of methylene blue and 60% of congo red dyes at initial concentration of 200 mg/L were decolorized within 16, 18 and 20 h, respectively by laccase immobilized in sol–gel matrix in the presence of 1-hydroxybenzotriazole (HBT) mediator. During the decolorization all three synthetic dyes showed various peaks on HPLC chromatogram indicating different by-products formation. Finally, phytotoxicity analysis results revealed that the by-products of synthetic dyes (formed during decolorization) showed less toxicity against Phaseolus mungo compared to untreated synthetic dyes.

Decolourisation Capabilities of Ligninolytic Enzymes Produced by Marasmius cladophyllus UMAS MS8 on Remazol Brilliant Blue R and Other Azo Dyes

Marasmius cladophyllus was examined for its ability to degradatively decolourise the recalcitrant dye Remazol Brilliant Blue R (RBBR) and screened for the production of ligninolytic enzymes using specific substrates. Monitoring dye decolourisation by the decrease in absorbance ratio of A₅₉₂/A₅₀₀ shows that the decolourisation of RBBR dye was associated with the dye degradation. Marasmius cladophyllus produces laccase and lignin peroxidase in glucose minimal liquid medium containing RBBR. Both enzyme activities were increased, with laccase activity recorded 70 times higher reaching up to 390 U L⁻¹ on day 12. Further in vitro RBBR dye decolourisation using the culture medium shows that laccase activity was correlated with the dye decolourisation. Fresh RBBR dye continuously supplemented into the decolourised culture medium was further decolourised much faster in the subsequent round of the RBBR dye decolourisation. In vitro dye decolourisation using the crude laccase not only decolourised 76% of RBBR dye in just 19 hours but also decolourised 54% of Orange G and 33% of Congo red at the same period of time without the use of any exogenous mediator. This rapid dye decolourisation ability of the enzymes produced by M. cladophyllus thus suggested its possible application in the bioremediation of dye containing wastewater.