Optimization of laccase production by Pleurotus ostreatus IMI 395545 using the Taguchi DOE methodology

Optimization of sustainable bioprocessing for the production of high-value biomolecules (chlorophylls and proteins) using Desmodesmus subspicatus

Traditional protein and pigment (e.g., chlorophyll) sources are becoming insufficient due to the rapid rise of the global population in modern civilization. Microalgae offer a promising solution for protein and chlorophyll sources due to their higher productivity than terrestrial plants. This study aims to optimize the cultivation conditions for Desmodesmus subspicatus, a microalgal strain containing ∼60% protein and 4% chlorophyll, to enhance biomass, protein and chlorophyll productivity. A Taguchi Orthogonal Array (TOA) was used for systematic optimization of BG-11 medium components. Further experiments assessed the effects of light intensity and different carbon and nitrogen sources. Under optimized BG-11 conditions, biomass increased 1.3-fold, with protein and chlorophyll productivity rising 2.25 and 1.92-fold, respectively. Supplementation with carbon and nitrogen sources under varying light (84-504 µmol m-2 s-1) further enhanced yields by 1.6-fold. Glycine proved to be the most effective nitrogen source, while cellulose as a carbon source resulted in 2.4-fold higher biomass, 7.3-fold higher protein, and 2.3-fold higher chlorophyll. Cytotoxicity assessment of the extracted chlorophyll revealed over 94% A549 cell viability at concentrations up to 100 µg/mL, confirming its biocompatibility. Therefore, Desmodesmus subspicatus has promise as a sustainable source of proteins and chlorophylls in the nutraceutical and food industries.

Enhancement for the synthesis of bio-energy molecules (carbohydrates and lipids) in Desmodesmus subspicatus: experiments and optimization techniques

Microalgae are regarded as renewable resources of energy, foods and high-valued compounds using a biorefinery approach. In the present study, we explored isolated microalgae (Desmodesmus subspicatus) for the production of bio-energy molecules (carbohydrate and lipid). Optimizations of media (BG-11) components have been made using the Taguchi orthogonal array (TOA) technique to maximize biomass, carbohydrate and lipid production. Optimized results showed that biomass, carbohydrates and lipid productivity increased by 1.3 times at optimal combinations of media components than standard BG-11 media. Further, the influence of various carbon and nitrogen sources as nutritional supplement with optimum media composition under different light intensities was investigated for productivity of carbohydrate and lipid. Results demonstrated that 1.5 times higher productivity of carbohydrate and lipids were achieved in the presence optimum BG-11 under a broad range of light intensities (84-504 µmol m-2 s-1). Among different nitrogen sources, glycine was found to give higher productivity (1.5 times) followed by urea. Use of the cellulose as a carbon source in the media significantly increases biomass (2.4 times), carbohydrates (2.3 times) and lipids (2.3 times) productivity. Investigations revealed that cultivating Desmodesmus subspicatus under optimum culture conditions has the potential for large-scale bio-ethanol and bio-diesel production.

Improved laccase production from Pleurotus floridanus using deoiled microalgal biomass: statistical and hybrid swarm-based neural networks modeling approach

Fungal laccases are versatile biocatalyst and occupy a prominent place in various industrial applications due to its broad substrate specificity. The simplest method to enhance the laccase production is by usage of cheap substrates in the fermentation processes incorporating modeling approaches for optimization. Integrated biorefinery concept is receiving wide popularity by making use of various products from microalgal biomass. The research aimed to identify the potential of deoiled microalgal biomass (DMB), a waste product from algal biorefinery as a nutrient supplement to enhance laccase production in Pleurotus floridanus by submerged fermentation. The maximum production was obtained in the presence of DMB as an additional nutrient supplement and copper sulfate as an inducer. The predictive capabilities of the two methodologies Response Surface Methodology (RSM) and hybrid Particle swarm optimization (PSO)-based Artificial Neural Network (ANN) were compared and validated. The results showed that ANN coupled with PSO predicted with more accuracy with an R 2 value of 0.99 than the RSM model with an R 2 value of 0.97. The optimized condition as predicted by superior model hybrid PSO-based ANN was glucose (3.51%), DMB (0.545%), pH (4.9), temperature (24.68 ℃) and CuSO4 (1.35 mM). The experimental laccase activity was 80.45 ± 0.132 U/mL which was 1.3 fold higher than unoptimized condition. This study promotes the usage of DMB as a novel supplement for the improved production of Pleurotus floridanus laccase.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03404-y.

Enhancement of growth and biomolecules (carbohydrates, proteins, and chlorophylls) of isolated Chlorella thermophila using optimization tools

The production of multiple products from microalgae is essential for economic sustainability and the knowledge of optimum cultivation conditions for high growth and biomolecule synthesis of a microalgal strain is the prerequisite for its commercial production. In this work, optimization of nutrient concentrations for the cultivation of isolated Chlorella thermophila was performed by manipulating nine nutrients with the objectives of maximization of growth, carbohydrate, protein, and chlorophyll contents. Experiments were designed and effects of the parameters were studied using Taguchi orthogonal array (TOA). Experimental results of TOA were used for modeling artificial neural networks (ANN) followed by the optimization using genetic algorithm (GA) to find global optimal solutions. Results showed an increase of 36, 88, 36, and 88% for growth, carbohydrates, proteins, and chlorophylls, respectively, at optimal combinations of parameters given by TOA. Results obtained through the ANN-GA optimization were 9, 10, and 3% more compared to the TOA for biomass, carbohydrates, and chlorophylls, respectively with experimental verification. Nitrates and bicarbonate were found to play the most pivotal role in biomass and biomolecule synthesis of the isolated microalgal strain. Results of the current investigation can be used in the industrial scale-up for the production of multiple products using the biorefinery approach.

Effect of Nutritional Factors and Copper on the Regulation of Laccase Enzyme Production in Pleurotus ostreatus

This research aimed to establish the relationship between carbon–nitrogen nutritional factors and copper sulfate on laccase activity (LA) by Pleurotus ostreatus. Culture media composition was tested to choose the nitrogen source. Yeast extract (YE) was selected as a better nitrogen source than ammonium sulfate. Then, the effect of glucose and YE concentrations on biomass production and LA as response variables was evaluated using central composite experimental designs with and without copper. The results showed that the best culture medium composition was glucose 45 gL⁻¹ and YE 15 gL⁻¹, simultaneously optimizing these two response variables. The fungal transcriptome was obtained in this medium with or without copper, and the differentially expressed genes were found. The main upregulated transcripts included three laccase genes (lacc2, lacc6, and lacc10) regulated by copper, whereas the principal downregulated transcripts included a copper transporter (ctr1) and a regulator of nitrogen metabolism (nmr1). These results suggest that Ctr1, which facilitates the entry of copper into the cell, is regulated by nutrient-sufficiency conditions. Once inside, copper induces transcription of laccase genes. This finding could explain why a 10–20-fold increase in LA occurs with copper compared to cultures without copper when using the optimal concentration of YE as nitrogen sources.

Combining analytical approaches for better lignocellulosic biomass degradation: a way of improving fungal enzymatic cocktails?

PURPOSE

In this study, a combinatory approach was undertaken to assay the efficiency of fungal enzymatic cocktails from different fermentation conditions to degrade different lignocellulosic biomasses with the aim of finely characterizing fungal enzymatic cocktails.

METHODS

Enzymatic assays (AZO and pNP-linked substrates and ABTS) were used to assess the composition of the fungal enzymatic cocktails for cellulase, xylanase and laccase activities. Comparisons were made with a new range of chromogenic substrates based on complex biomass (CBS substrates). The saccharification efficiency of the cocktails was evaluated as a quantification of the sugar monomers released from the different biomasses after incubation with the enzymatic cocktails.

RESULTS

The results obtained showed striking differences between the AZO and pNP-linked substrates and the CBS substrates for the same enzymatic cocktails. On AZO and pNP-linked substrates, different hydrolysis profiles were observed between the different fungi species with Aspergillus oryzae being the most efficient. However, the results on CBS substrates were more contrasted depending on the biomass tested. Altogether, the results highlighted that assessing laccase activities and taking into account the complexity of the biomass to degrade were key in order to provide the best enzymatic cocktails.

CONCLUSION

The complementary experiments performed in this study showed that different approaches needed to be taken in order to accurately assess the ability of an enzymatic cocktail to be efficient when it comes to lignocellulosic biomass degradation. The saccharification assay proved to be essential to validate the data obtained from both simple and complex substrates.

Chemo-metric engineering designs for deciphering the biodegradation of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are non-polar organic compounds that are omnipresent in the environment and released due to anthropogenic activities through emissions and discharges. PAHs, being xenobiotic and exerts health impacts, thus they attract serious concern by the environmentalists. The stringent regulations and the need of sustainable development urges the hunt for a technically feasible and cost-effective wastewater treatment. Although the conventional physico-chemical treatment are widely preferred, they cause secondary pollution problems and demand subsequent treatment options. This comprehensive review intends to address the (a) different PAHs and their associated toxicity, (b) the remedial strategies, particularly biodegradation. The biological wastewater treatment techniques that involve microbial systems are highly influenced by the different physio-chemical and environmental parameters. Therefore, suitable optimization techniques are prerequisite for effective functioning of the biological treatment that sustains judiciously and interpreted in a lesser time. Here we have aimed to discuss (a) different chemo-metric tools involved in the design of experiments (DoE), (b) design equations and models, (c) tools for evaluating the model's adequacy and (d) plots for graphically interpreting the chemo-metric designs. However, to best of our knowledge, this is a first review to discuss the PAHs biodegradation that are tailored by chemo-metric designs. The associated challenges, available opportunities and techno-economic aspects of PAHs degradation using chemo-metric engineering designs are explained. Additionally, the review highlights how well these DoE tools can be suited for the sustainable socio-industrial sectors. Concomitantly, the futuristic scope and prospects to undertake new areas of research exploration were emphasized to unravel the least explored chemo-metric designs.

Partial purification and characterization of a thermophilic and alkali-stable laccase of Phoma herbarum isolate KU4 with dye-decolorization efficiency

Production of an extracellular thermophilic and alkali stable laccase from Phoma herbarum isolate KU4 was reported for the first time, both in submerged fermentation (SmF, highest 1590 U/mL) and solid state fermentation (SSF, highest 2014.21 U/mL) using agro-industrial residues. The laccase was partially purified to 7.93 fold with the apparent molecular weight of 298 kDa. The enzyme had pH optimum at 5.0 and temperature optimum at 50 °C, with maximum stability at pH 8.0. It showed activity towards various phenolic and non-phenolic compounds. The kinetic parameters, K_m, V_max and K_cat of the laccase for DMP were 0.216 mM, 270.27 U/mg and 506.69 s^-1, respectively. Laccase activity was inhibited by various metal ions and conventional inhibitors, however, it was slightly increased by Zn²⁺. The laccase showed good decolorization efficiency towards four industrial dyes, namely, methyl violet (75.66%), methyl green (65%), indigo carmine (58%) and neutral red (42%) within 24 h. FTIR analysis of the decolorized products confirmed the degradation of the dyes. The decolorization efficiency of the enzyme suggests that the partially purified laccase could be used to decolorize synthetic dyes present in industrial effluents and for waste water treatments. The thermophilic and alkali stable laccase may also have wider potential industrial applications.

Accelerating the Biodegradation of High-Density Polyethylene (HDPE) Using Bjerkandera adusta TBB-03 and Lignocellulose Substrates

High-density polyethylene (HDPE) is a widely used organic polymer and an emerging pollutant, because it is very stable and nonbiodegradable. Several fungal species that produce delignifying enzymes are known to be promising degraders of recalcitrant polymers, but research on the decomposition of plastics is scarce. In this study, white rot fungus, Bjerkandera adusta TBB-03, was isolated and characterized for its ability to degrade HDPE under lignocellulose substrate treatment. Ash (Fraxinus rhynchophylla) wood chips were found to stimulate laccase production (activity was > 210 U/L after 10 days of cultivation), and subsequently used for HDPE degradation assay. After 90 days, cracks formed on the surface of HDPE samples treated with TBB-03 and ash wood chips in both liquid and solid states. Raman analysis showed that the amorphous structure of HDPE was degraded by enzymes produced by TBB-03. Overall, TBB-03 is a promising resource for the biodegradation of HDPE, and this work sheds light on further applications for fungus-based plastic degradation systems.

Pre-treatment of a sugarcane bagasse-based substrate prior to saccharification: Effect of coffee pulp and urea on laccase and cellulase activities of Pycnoporus sanguineus

Production of second-generation bioethanol uses lignocellulose from agricultural by-products such as sugarcane bagasse (SCB). A lignocellulose pre-treatment is required to degrade lignin, ensuring further efficient saccharification. Two experimental designs were set up to define culture conditions of Pycnoporus sanguineus in mesocosms to increase laccase activities and thus delignification. The first experimental design tested the effect of phenolic complementation (via coffee pulp) and the use of urea as a simple nitrogen source and the second defined more precisely the percentages of coffee pulp and urea to enhance delignification. The responses measured were: lignocellulolytic activities, laccase isoform profiles by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the chemical transformation of the substrate using solid-state NMR of 13C. Adding 10% of coffee pulp increased laccase activities and fungal biomass (32.5% and 16% respectively), enhanced two constitutive isoforms (R_f 0.23 and 0.27), induced a new isoform (R_f 0.19) and led to a decrease in total aromatics. However, higher concentrations of coffee pulp (25%) decreased laccase and cellulase activities but no decrease in aromaticity was observed, potentially due to the toxic effect of phenols from coffee pulp. Moreover, laccase production was still inhibited even for lower concentrations of urea (0-5%). Our findings revealed that an agricultural by-product like coffee pulp can enhance laccase activity -though to a threshold- and that urea limited this process, indicating that other N-sources should be tested for the biological delignification of SCB.

Optimization of non-detergent treatment for enveloped virus inactivation using the Taguchi design of experimental methodology (DOE)

In mammalian cell culture technology, viral contamination is one of the main challenges; and, so far, various strategies have been taken to remove or inactivate viruses in the cell-line production process. The suitability and feasibility of each method are determined by different factors including effectiveness in target virus inactivation, maintaining recombinant protein stability, easiness-in terms of the process condition, cost-effectiveness, and eco-friendliness. In this research, Taguchi design-of-experiments (DOE) methodology was used to optimize a non-detergent viral inactivation method via considering four factors of temperature, time, pH, and alcohol concentration in an unbiased (orthogonal) fashion with low influence of nuisance factors. Herpes Simplex Virus-1 (HSV1) and Vero cell-line were used as models for enveloped viruses and cell-line, respectively. Examining the cytopathic effects (CPE) in different dilutions showed that pH (4), alcohol (15%), time (120 min), and temperature (25 °C) were the optimal points for viral inactivation. Evaluating the significance of each parameter in the HSV-1 inactivation using Taguchi and ANOVA analyses, the contributions of pH, alcohol, temperature and time were 56.5%, 19.2%, 12%, and 12%, respectively. Examining the impact of the optimal viral treatment condition on the stability of model recombinant protein-recombinant human erythropoietin, no destabilization was detected.

Laccase production from sucrose by recombinant Yarrowia lipolytica and its application to decolorization of environmental pollutant dyes

Laccases are used in decolorization and biodegradation of synthetic dyes, bioremediation of industrial wastewaters and delignification of lignocellulosic compounds. The aims of the present study were the optimization of a recombinant laccase production in Yarrowia lipolytica yeast using sucrose as a main carbon source, and the application of the resulting enzyme to decolorization of synthetic dyes, which are problematic environmental pollutants. Taguchi's experimental design method was employed to optimize medium compounds. Recombinant laccase production by Y. lipolytica YL4 strain increased to 900 U L^-1 after optimization of sucrose, ammonium chloride, yeast extract and thiamine levels in the modified PPB medium. Furthermore, the production rate reached 6760 U L^-1 in a 5 L bioreactor which represents 4.5- and 33.5-fold increases compared to cultures that were in shake-flask with optimized and primary media, respectively. The supernatant containing secreted recombinant laccase was applied for decolorization of seven dyes. The effects of pH, the amount of enzyme and incubation period were verified. The effect of incubation time on dye decolorization by recombinant laccase was important, which has an influence of greater extent than 90% after 48 h for all dyes. The Trametes versicolor laccase can be efficiently produced in Y. lipolytica and the recombinant enzyme has a considerable potential in the decolorization of pollutant synthetic dyes.

Gongronella sp. w5 elevates Coprinopsis cinerea laccase production by carbon source syntrophism and secondary metabolite induction

When sucrose was used as the carbon source, the Basidiomycete Coprinopsis cinerea showed poor growth and low laccase activity in pure culture, but greatly enhanced the level of laccase activity (>1800 U/L) during coculture with the Mucoromycete Gongronella sp. w5. As a result, the mechanism of laccase overproduction in coculture was investigated by starting from clarifying the function of sucrose. Results demonstrated that Gongronella sp. w5 in the coculture system hydrolyzed sucrose to glucose and fructose by an intracellular invertase. Fructose rather than glucose was supplied by Gongronella sp. w5  as the readily available carbon source for C. cinerea, and contributed to an alteration of its growth behavior and a basal laccase secretion of 110.6 ± 3.3 U/L. On the other hand, separating Gongronella sp. w5 of C. cinerea by transfer into dialysis tubes yielded the same level of laccase activity as without separation, indicating that enhanced laccase production probably resulted from the metabolites in the fermentation broth. Further investigation showed that the ethyl acetate-extracted metabolites generated by Gongronella sp. w5 induced C. cinerea laccase production. One of the laccase-inducing compounds namely p-hydroxybenzoic acid (HBA) was purified and identified from the extract. When using HBA as the inducer and fructose as the carbon source in monoculture, C. cinerea observed similar high laccase activity to that in coculture, and zymograms revealed the same expression of laccase Lcc9 as the main and Lcc1 and Lcc5 as the minor enzymes. Overall, our experiments verified that Gongronella sp. w5 elevates Coprinopsis cinerea laccase production by carbon source syntrophism and secondary metabolite induction.

Fungal co-culture increases ligninolytic enzyme activities: statistical optimization using response surface methodology

The optimization of ligninolytic enzyme (LE) activities in a novel fungal co-culture between Pycnoporus sanguineus and Beauveria brongniartii were studied using a Plackett-Burman experimental design (PBED) and a central composite design (CCD). In addition, H₂O₂ role was analyzed. Laccase (EC. 1.10.3.2) and MnP (EC 1.11.1.14) activities of P. sanguineus increased 6.0- and 2.3-fold, respectively, in the co-culture with B. brongniartii. The H₂O₂ content was higher in the co-culture (0.33-7.12-fold) than in the P. sanguineus monoculture. The PBED revealed that yeast extract (YE), FeSO_4, and inoculum amount were significant factors for laccase and MnP activities and H₂O₂ production in the co-culture, which increased by 8.2-, 5.2- and 1.03-fold, respectively. The YE and FeSO₄ were studied using a CCD to optimize the studied response variables. Laccase activity was enhanced 1.5-fold by CCD, the optimal amount of YE was 0.366 g L^-1. Quadratic term of FeSO₄ modulated MnP activity and was associated with a 4.28-fold increase compared to the PBED. Both YE and its quadratic term significantly affected H₂O₂ production; however, the CCD did not enable an increase in H₂O₂ production. Pearson correlation indicated an increase in laccase (r²=0.4411, p = 0.0436) and MnP (r²=0.5186, p = 0.0198) activities following increases in H₂O₂ in the co-culture system.

Bioremediation of chlorpyrifos contaminated soil by two phase bioslurry reactor: Processes evaluation and optimization by Taguchi's design of experimental (DOE) methodology

Two phase bioreactor was constructed, designed and developed to evaluate the chlorpyrifos remediation. Six biotic and abiotic factors (substrate-loading rate, slurry phase pH, slurry phase dissolved oxygen (DO), soil water ratio, temperature and soil micro flora load) were evaluated by design of experimental (DOE) methodology employing Taguchi's orthogonal array (OA). The selected six factors were considered at two levels L-8 array (2^7, 15 experiments) in the experimental design. The optimum operating conditions obtained from the methodology showed enhanced chlorpyrifos degradation from 283.86µg/g to 955.364µg/g by overall 70.34% of enhancement. In the present study, with the help of few well defined experimental parameters a mathematical model was constructed to understand the complex bioremediation process and optimize the approximate parameters upto great accuracy.

Delignification and detoxification of peanut shell bio-waste using an extremely halophilic laccase from an Aquisalibacillus elongatus isolate

Lignocellulose bioconversion is a harsh process requiring the use of surfactants and organic solvents. Consequently, the incorporation of laccases in this bioconversion requires the bioprospecting of enzymes that can remain stable under extreme conditions. An extracellular, highly stable laccase was produced by the halophilic isolate Aquisalibacillus elongatus in submerged liquid culture fermentation. Statistical and non-statistical strategies gave the highest enzymatic activity (8.02 U mL^-1) following addition of glucose (1.7 g L^-1), copper sulfate (0.8 g L^-1), urea (15 g L^-1), and CaCl₂ (0.8 g L^-1). The enzyme, after purification using a synthetic affinity support, delignified a peanut shell substrate by 45%. A pH of 8.0 and a temperature of 35 °C were optimal for delignification of this bio-waste material. Addition of [Bmim][PF₆], 1,4-dioxane, acetone, and HBT promoted this bio-waste delignification. Bio-treatment in the presence of 50% [Bmim][PF₆] gave a maximal lignin removal of 87%. The surfactants tested had no significant effects on the delignification yield. The laccase also detoxified the toxic phenols found in peanut shell waste. The high catalytic efficiency of this enzyme against a lignocellulosic sample under extreme conditions suggests the suitability of this laccase for industrial applications.

Yeast Hosts for the Production of Recombinant Laccases: A Review

Laccases are multi-copper oxidoreductases which catalyze the oxidation of a wide range of substrates during the simultaneous reduction of oxygen to water. These enzymes, originally found in fungi, plants, and other natural sources, have many industrial and biotechnological applications. They are used in the food, textile, pulp, and paper industries, as well as for bioremediation purposes. Although natural hosts can provide relatively high levels of active laccases after production optimization, heterologous expression can bring, moreover, engineered enzymes with desired properties, such as different substrate specificity or improved stability. Hence, diverse hosts suitable for laccase production are reviewed here, while the greatest emphasis is placed on yeasts which are commonly used for industrial production of various proteins. Different approaches to optimize the laccase expression and activity are also discussed in detail here.

Effect of textile dyes on activity and differential regulation of laccase genes from Pleurotus ostreatus grown in submerged fermentation

This research was conducted to extend the knowledge on the differential regulation of laccase genes in response to dyes. In order to accomplish this, we analyzed both, the expression of five laccase genes by real time RT-qPCR, and also the laccase activity and isoforms patterns during the time-course of a Pleurotus ostreatus submerged fermentation supplemented with either acetyl yellow G (AYG) or remazol brilliant blue R (RBBR) dyes. For the purpose of obtaining a stable reference gene for optimal normalization of RT-quantitative PCR gene expression assays, we tested four candidate reference genes. As a result of this analysis, gpd was selected as reference index for data normalization. The addition of dyes had an induction effect on the enzymatic activity and also modified the zymogram profile. Fermentation with RBBR showed the highest laccase activity and number of isoforms along the course of the fermentation. Laccase gene expression profiles displayed up/down regulation along the fermentation time in four laccase genes (pox4, pox3, poxa1b and pox2), while pox1 was not expressed in either of the fermentation conditions. AYG addition caused the highest induction and repression levels for genes pox3 and poxa1b respectively. The expression level for all genes in the presence of RBBR were lower than in AYG, being in both conditions this response growth time dependent. These results show the influence of the nature of dyes on the induction level of laccase activity and on the differential regulation of the laccase genes expression in P. ostreatus.

Laccase production and metabolic diversity among Flammulina velutipes strains

Twelve Flammulina velutipes strains originating from Poland were identified using internal transcribed spacer (ITS) region sequencing. Based on the sequences obtained, the genomic relationship of the analyzed strains was determined. All F. velutipes strains were also characterized using Biolog FF MicroPlates to obtain data on C-substrate utilization and mitochondrial activity. The ability to decompose various substrates differed among the F. velutipes strains up to five times. The highest catabolic activities were characteristic for only two strains with capabilities to decompose up to 22 carbon sources. The correlation between carbon repression and laccase production by F. velutipes was analyzed based on glucose assimilation by these strains. Moreover, the influence of metal ions (Cu(2+), Cd(2+)), veratric and ferulic acids, and temperature on laccase activities in the analyzed strains was determined. The results obtained proved that all the inducers influenced laccase expression in almost all the analyzed strains. However, the degree of induction depended not only on the strain used but also on the day of the induction.

Fungal laccases and their applications in bioremediation

Laccases are blue multicopper oxidases, which catalyze the monoelectronic oxidation of a broad spectrum of substrates, for example, ortho- and para-diphenols, polyphenols, aminophenols, and aromatic or aliphatic amines, coupled with a full, four-electron reduction of O₂ to H₂O. Hence, they are capable of degrading lignin and are present abundantly in many white-rot fungi. Laccases decolorize and detoxify the industrial effluents and help in wastewater treatment. They act on both phenolic and nonphenolic lignin-related compounds as well as highly recalcitrant environmental pollutants, and they can be effectively used in paper and pulp industries, textile industries, xenobiotic degradation, and bioremediation and act as biosensors. Recently, laccase has been applied to nanobiotechnology, which is an increasing research field, and catalyzes electron transfer reactions without additional cofactors. Several techniques have been developed for the immobilization of biomolecule such as micropatterning, self-assembled monolayer, and layer-by-layer techniques, which immobilize laccase and preserve their enzymatic activity. In this review, we describe the fungal source of laccases and their application in environment protection.

Laccase production by Coriolopsis caperata RCK2011: optimization under solid state fermentation by Taguchi DOE methodology

Laccase production by Coriolopsis caperata RCK2011 under solid state fermentation was optimized following Taguchi design of experiment. An orthogonal array layout of L18 (2(1) × 3(7)) was constructed using Qualitek-4 software with eight most influensive factors on laccase production. At individual level pH contributed higher influence, whereas, corn steep liquor (CSL) accounted for more than 50% of the severity index with biotin and KH2PO4 at the interactive level. The optimum conditions derived were; temperature 30°C, pH 5.0, wheat bran 5.0 g, inoculum size 0.5 ml (fungal cell mass = 0.015 g dry wt.), biotin 0.5% w/v, KH2PO4 0.013% w/v, CSL 0.1% v/v and 0.5 mM xylidine as an inducer. The validation experiments using optimized conditions confirmed an improvement in enzyme production by 58.01%. The laccase production to the level of 1623.55 Ugds(-1) indicates that the fungus C. caperata RCK2011 has the commercial potential for laccase.

Induction and transcriptional regulation of laccases in fungi

Fungal laccases are phenol oxidases widely studied for their use in several industrial applications, including pulp bleaching in paper industry, dye decolourisation, detoxification of environmental pollutants and revalorization of wastes and wastewaters. The main difficulty in using these enzymes at industrial scale ensues from their production costs. Elucidation of the components and the mechanisms involved in regulation of laccase gene expression is crucial for increasing the productivity of native laccases in fungi. Laccase gene transcription is regulated by metal ions, various aromatic compounds related to lignin or lignin derivatives, nitrogen and carbon sources. In this manuscript, most of the published results on fungal laccase induction, as well as analyses of both the sequences and putative functions of laccase gene promoters are reviewed. Analyses of promoter sequences allow defining a correlation between the observed regulatory effects on laccase gene transcription and the presence of specific responsive elements, and postulating, in some cases, a mechanism for their functioning. Only few reports have investigated the molecular mechanisms underlying laccase regulation by different stimuli. The reported analyses suggest the existence of a complex picture of laccase regulation phenomena acting through a variety of cis acting elements. However, the general mechanisms for laccase transcriptional regulation are far from being unravelled yet.