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

A systematic study on the characteristics and applications of laccases produced by fungi: insights on their potential for biotechnologies

Laccases are polyphenol oxidase enzymes and form the enzyme complex known for their role in wood decomposition and lignin degradation. The present study aimed to systematically review the state-of-the-art trends in scientific publications on laccase enzymes of the last 10 years. The main aspects checked included the laccase-producing fungal genera, the conditions of fungal growth and laccase production, the methods of immobilization, and potential applications of laccase. After applying the systematic search method 177 articles were selected to compound the final database. Although various fungi produce laccase, most studies were Trametes and Pleurotus genera. The submerged fermentation (SmF) has been the most used, however, the use of solid-state fermentation (SSF) appeared as a promising technique to produce laccase when using agro-industrial residues as substrates. Studies on laccase immobilization showed the covalent bonding and entrapment methods were the most used, showing greater efficiency of immobilization and a high number of enzyme reuses. The main use of the laccase was in bioremediation, especially in the discoloration of dyes from the textile industry and the degradation of pharmaceutical waste. Implications and consequences of all these findings in biotechnology and environment, as well as the trends and gaps of laccase research were discussed.

Effects of potential inducers to enhance laccase production and evaluating concomitant enzyme immobilisation

This work investigated non-polar solvent hexane and polar solvents methanol and ethanol as inducers besides a well-known inducer, copper, for laccase production with and without mesoporous silica-covered plastic packing under sterilised and unsterilised conditions. The potential of waste-hexane water, which is generated during the mesoporous silica production process, was also investigated as a laccase inducer. During the study, the free and immobilised laccase activity on the packing was measured. The results showed that the highest total laccase activity, approximately 10,000 Units, was obtained under sterilised conditions with 0.5 mM copper concentration. However, no immobilised laccase activity was detected except in the copper and ethanol sets under unsterilised conditions. The maximum immobilised laccase activity of the sets that used waste hexane as an inducer was 1.25 U/mg packing. According to its significant performance, waste hexane can be an alternative inducer under sterilised conditions. Concomitant immobilised packing showed satisfactory laccase activities and could be a promising method to reduce operation costs and improve the cost-efficiency of enzymatic processes in wastewater treatment plants.

Effects of Orange Peel Extract on Laccase Activity and Gene Expression in Trametes versicolor

The genome of Trametes versicolor encodes multiple laccase isozymes, the expression of which is responsive to various conditions. Here, we set out to investigate the potential of orange peel extract as an inducer of laccase production in this white-rot fungus, in comparison to the previously identified inducing chemical compound, veratryl alcohol. For four geographically distinct T. versicolor strains, a positive correlation has been observed between their oxidative activity and incubation time in liquid cultures. The addition of 20% orange peel extract or 5 mM veratryl alcohol caused a rapid increase in the oxidative potential of T. versicolor M99 after 24 h, with a more pronounced effect observed for the orange peel extract. To elucidate the underlying molecular mechanisms of the induced laccase activity, a transcriptional gene expression analysis was performed for the seven individual laccase genes in T. versicolor, revealing the upregulation of several laccase genes in response to the addition of each inducer. Notably, the gene encoding TvLac5 demonstrated a substantial upregulation in response to the addition of 20% orange peel extract, likely contributing to the observed increase in its oxidative potential. In conclusion, our results demonstrate that orange peels are a promising agro-industrial side stream for implementation as inducing agents in large-scale laccase production with T. versicolor.

Laccase immobilization and its degradation of emerging pollutants: A comprehensive review

The chronic lack of effective disposal of pollutants has resulted in the detection of a wide variety of EPs in the environment, with concentrations high enough to affect ecological health. Laccase, as a versatile oxidase capable of catalyzing a wide range of substrates and without producing toxic by-products, is a potential candidate for the biodegradation of pollutants. Immobilization can provide favorable protection for free laccase, improve the stability of laccase in complex environments, and greatly enhance the reusability of laccase, which is significant in reducing the cost of industrial applications. This study introduces the properties of laccase and subsequently elaborate on the different support materials for laccase immobilization. The research advances in the degradation of EDs, PPCPs, and PAHs by immobilized laccase are then reviewed. This review provides a comprehensive understanding of laccase immobilization, as well as the advantages of various support materials, facilitating the development of more economical and efficient immobilization systems that can be put into practice to achieve the green degradation of EPs.

In silico and in vitro assays suggests Congo red dye degradation by a Lentinus sp. laccase enzyme

Laccase is a superfamily of ligninolytic enzymes known to degrade a wide variety of xenobiotics, including synthetic dyes. Congo Red (CR) has a diazo dye function, carcinogenic and mutagenic potential, and is currently applied in clinical analysis. The objective of this work was to produce and characterize the crude extract of Lentinus sp. in semi-solid fermentation (FSS) and perform in vitro and in silico studies to assess the potential of the crude extract to discolor the CR dye. Laccase activity was determined using ABTS as substrate and characterized. The in vitro discoloration was carried out using experimental design 22 at room temperature and monitored at 340 nm for 24h. Molecular docking and molecular dynamics simulations were performed between laccase and CR. The maximum laccase activity production was 29.63 U L-1 with six days of FSS. The optimal temperature and pH were 50 °C and 3.0, respectively. Discoloration of the CR dye was obtained only in tests containing CuSO4. Laccase formed stable complexes with the dye, presenting negative binding energy values ranging from -70.94 to -63.16 kcal mol-1 and the occurrence of seven hydrogen bonds. Molecular dynamics results showed the stability of the system (RMSD ranging from 1.0 to 2.5 Ä) and protein-ligand interaction along simulation. RMSF values pointed residues at the end of chains A (residues 300 to 305, 480 to 500) and B (residues 650 to 655 and 950 to 1000) as the most flexible regions of the laccase. This study highlighted the enzymatic action in the bioremediation of CR in vitro in agreement with the in silico simulations that demonstrate the enzyme potential.Communicated by Ramaswamy H. Sarma.

Fungal Laccases: Fundamentals, Engineering and Classification Update

Multicopper oxidases (MCOs) share a common catalytic mechanism of activation by oxygen and cupredoxin-like folding, along with some common structural determinants. Laccases constitute the largest group of MCOs, with fungal laccases having the greatest biotechnological applicability due to their superior ability to oxidize a wide range of aromatic compounds and lignin, which is enhanced in the presence of redox mediators. The adaptation of these versatile enzymes to specific application processes can be achieved through the directed evolution of the recombinant enzymes. On the other hand, their substrate versatility and the low sequence homology among laccases make their exact classification difficult. Many of the ever-increasing amounts of MCO entries from fungal genomes are automatically (and often wrongly) annotated as laccases. In a recent comparative genomic study of 52 basidiomycete fungi, MCO classification was revised based on their phylogeny. The enzymes clustered according to common structural motifs and theoretical activities, revealing three novel groups of laccase-like enzymes. This review provides an overview of the structure, catalytic activity, and oxidative mechanism of fungal laccases and how their biotechnological potential as biocatalysts in industry can be greatly enhanced by protein engineering. Finally, recent information on newly identified MCOs with laccase-like activity is included.

Optimization of laccase from Stenotrophomonas maltophilia E1 by submerge fermentation using coconut husk with its detoxification and biodecolorization ability of synthetic dyes

Enzymatic degradation of synthetic dyes holds an immense promise for addressing the environmental concerns associated with the textile and dye industries. This study aimed to isolate bacteria capable of producing laccase enzymes from an anthropogenic environment. Subsequently, viability of utilizing cost-effective agricultural residues as substrates for laccase production was assessed. Response Surface Methodology (RSM) and the One Variable at a Time (OVAT) approach was pursued for the optimization of laccase production, followed by pH and temperature stability, dye degradation and decolorization experiments, toxicological studies on the degraded dye metabolites. In results, laccase-producing bacterial strain was identified as Stenotrophomonas maltophilia strain E1 (S. maltophilia). Among variety of substrates, coconut husk exhibited optimal efficacy. In a statistical optimization study, it was found that S. maltophilia was capable of producing laccase 51.38 IU/mL, i.e., three times higher than the amount of laccase produced by unoptimized medium (16.7 IU/mL), and the enzyme activity was found to be steady at an acidic pH, and a mesophilic temperature range. The laccase obtained from S. maltophilia E1 demonstrated proficient dye decolorization capabilities, achieving a notable 92.1% reduction in Malachite green dye coloration at a concentration of 500 ppm. Gas chromatography-mass spectrometry (GC-MS) analysis of the decolorized derivatives of Malachite green revealed a conversion into a distinct compounds. Moreover, after undergoing laccase treatment, Malachite green exhibited decreased phytotoxic effects on Oryza sativa, pointing to enzymatic detoxification. Collectively, insights gained from the present study will contribute to the development of efficient enzymatic approaches for addressing the environmental pollution caused by synthetic dyes.

Improvement of aflatoxin B1 degradation ability by Bacillus licheniformis CotA-laccase Q441A mutant

Aflatoxin B1 (AFB1) contamination seriously threatens nutritional safety and common health. Bacterial CotA-laccases have great potential to degrade AFB1 without redox mediators. However, CotA-laccases are limited because of the low catalytic activity as the spore-bound nature. The AFB1 degradation ability of CotA-laccase from Bacillus licheniformis ANSB821 has been reported by a previous study in our laboratory. In this study, a Q441A mutant was constructed to enhance the activity of CotA-laccase to degrade AFB1. After the site-directed mutation, the mutant Q441A showed a 1.73-fold higher catalytic efficiency (kcat/Km) towards AFB1 than the wild-type CotA-laccase did. The degradation rate of AFB1 by Q441A mutant was higher than that by wild-type CotA-laccase in the pH range from 5.0 to 9.0. In addition, the thermostability was improved after mutation. Based on the structure analysis of CotA-laccase, the higher catalytic efficiency of Q441A for AFB1 may be due to the smaller steric hindrance of Ala441 than Gln441. This is the first research to enhance the degradation efficiency of AFB1 by CotA-laccase with site-directed mutagenesis. In summary, the mutant Q441A will be a suitable candidate for highly effective detoxification of AFB1 in the future.

A Novel Two-Domain Laccase with Middle Redox Potential: Physicochemical and Structural Properties

The gene for a previously unexplored two-domain laccase was identified in the genome of actinobacterium Streptomyces carpinensis VKM Ac-1300. The two-domain laccase, named ScaSL, was produced in a heterologous expression system (Escherichia coli strain M15 [pREP4]). The enzyme was purified to homogeneity using affinity chromatography. ScaSL laccase, like most two-domain laccases, exhibited activity in the homotrimer form. However, unlike the most two-domain laccases, it was also active in multimeric forms. The enzyme exhibited maximum activity at 80°C and was thermally stable. Half-inactivation time of ScaSL at 80°C was 40 min. The laccase was able to oxidize a non-phenolic organic compound ABTS at a maximum rate at pH 4.7, and to oxidized a phenolic compound 2,6-dimethoxyphenol at a maximum rate at pH 7.5. The laccase stability was observed in the pH range 9-11. At pH 7.5, laccase was slightly inhibited by sodium azide, sodium fluoride, and sodium chloride; at pH 4.5, the laccase was completely inhibited by 100 mM sodium azide. The determined Km and kcat of the enzyme for ABTS were 0.1 mM and 20 s-1, respectively. The Km and kcat for 2,6-dimethoxyphenol were 0.84 mM and 0.36 s-1, respectively. ScaSL catalyzed polymerization of humic acids and lignin. Redox potential of the laccase was 0.472 ± 0.007 V. Thus, the ScaSL laccase is the first characterized two-domain laccase with a middle redox potential. Crystal structure of ScaSL was determined with 2.35 Å resolution. Comparative analysis of the structures of ScaSL and other two-domain laccases suggested that the middle potential of ScaSL may be associated with conformational differences in the position of the side groups of amino acids at position 230 (in ScaSL numbering), which belong to the second coordination sphere of the copper atom of the T1 center.

Laccase-Based Self-Amplifying Catalytic System Enables Efficient Antibiotic Degradation for Sustainable Environmental Remediation

Antibiotic contamination poses potential risks to ecosystems and human health. Laccase (LAC) has emerged as a promising biocatalyst for the oxidation of environmentally toxic contaminants with high catalytic efficiency; however, its large-scale application is hindered by enzyme costs and dependency on redox mediators. Herein, a novel self-amplifying catalytic system (SACS) for antibiotic remediation that does not require external mediators is developed. In SACS, a natural mediator-regenerating koji with high-activity LAC, derived from lignocellulosic waste, initiates the chlortetracycline (CTC) degradation. Subsequently, an intermediate product, CTC327, identified as an active mediator for LAC via molecular docking, is formed and then starts a renewable reaction cycle, including CTC327-LAC interaction, stimulated CTC bioconversion, and self-amplifying CTC327 release, thus enabling highly efficient antibiotic bioremediation. In addition, SACS exhibits excellent performance in producing lignocellulose-degrading enzymes, highlighting its potential for lignocellulosic biomass deconstruction. To demonstrate its effectiveness and accessibility in the natural environment, SACS is used to catalyze in situ soil bioremediation and straw degradation. The resulting CTC degradation rate is 93.43%, with a straw mass loss of up to 58.35% in a coupled process. This mediator regeneration and waste-to-resource conversion in SACS provides a promising route for environmental remediation and sustainable agricultural practices.

Sorghum-grown fungal biocatalysts for synthetic dye degradation

The synthetic dye discharge is responsible for nearly one-fifth of the total water pollution from textile industry, which poses both environmental and public health risks. Herein, a solid substrate inoculated with fungi is proposed as an effective and environmentally friendly approach for catalyzing organic dye degradation. Pleurotus ostreatus was inoculated onto commercially available solid substrates such as sorghum, bran, and husk. Among these, P. ostreatus grown on sorghum (PO-SORG) produced the highest enzyme activity and was further tested for its dye biodegradation ability. Four dye compounds, Reactive Blue 19 (RB-19), Indigo Carmine, Acid Orange 7, and Acid Red 1 were degraded by PO-SORG with removal efficiencies of 93%, 95%, 95%, and 78%, respectively. Under more industrially relevant conditions, PO-SORG successfully degraded dyes in synthetic wastewater and in samples collected from a local textile factory, which reveals its potential for practical usage. Various biotransformation intermediates and end-products were identified for each dye. PO-SORG exhibited high stability even under relatively extreme temperatures and pH conditions. Over 85% removal of RB-19 was achieved after three consecutive batch cycles, demonstrating reusability of this approach. Altogether, PO-SORG demonstrated outstanding reusability and sustainability and offers considerable potential for treating wastewater streams containing synthetic organic dyes.

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.

Using green waste as substrate to produce biostimulant and biopesticide products through solid-state fermentation

Although the use of green waste as a substrate in different types of microbial bioprocessing has a major impact on improving green waste valorization, very little information has been provided on this issue. The purpose of this paper is to study the feasibility of using green waste to produce a biostimulant (Indole-3-acetic acid (IAA)) and biopesticide (conidial spore) through solid-state fermentation. Trichoderma harzianum was selected as the inoculum of the process and the green waste was a mixture of grass clippings and pruning waste. An experiment was designed to study the effect of tryptophan concentration, proportion of grass and pruning waste, and substrate moisture on IAA and spore production. The results show that washing and using phosphate buffer has a beneficial effect on green waste quality in terms of bioproduction. The maximum IAA and spore productions reported in the current study were 101.46 µg g^-1 dry matter and 3.03 × 10⁹ spore g^-1 dry matter, respectively. According to the results, IAA production increases with a higher amount of tryptophan and grass. However, the number of spores increased with lower amounts of tryptophan and grass. The model suggested the following optimized parameters for the production of spores and IAA: tryptophan 0.45 %, grass 61 %, and moisture 74 %. The effect of fermentation time was also studied, and the results show that the maximum IAA and spore production was obtained on days 3 and 7, respectively.

Dual inoculation with rhizosphere-promoting bacterium Bacillus cereus and beneficial fungus Peniophora cinerea improves salt stress tolerance and productivity in willow

Utilization of rhizosphere microorganisms to improve plant growth and salt tolerance has recently attracted widespread attention. The growth and salt tolerance of willows inoculated with Bacillus cereus JYZ-SD2 and Peniophora cinerea XC were studied under different salt stress conditions. The results showed that the chlorophyll content of willow cuttings inoculated with the XC strain increased significantly by 51.27%. After salt stress of willow cuttings inoculated with B. cereus JYZ-SD2 and P. cinerea XC (solely or in combination), the amount of sodium in the roots from the epidermis to the pericycle decreased and the content of sodium in the pericycle was significantly lower than that of the uninoculated willow, while the proportion of potassium increased. Willow cuttings inoculated with microorganisms showed increased activity of SOD and POD. At the salt concentration of 100 mmol/L, the highest SOD activity was found in B. cereus JYZ-SD2-inoculated willows, with 59.88% increase compared to uninoculated willows; the highest POD activity was found in P. cinerea XC and B. cereus JYZ-SD2 co-inoculated willows, with 51.05% increase compared to uninoculated willows. The Na-K-ATPase and Ca-Mg-ATPase activities of inoculated P. cinerea XC willow cuttings were also 59.38% and 60% higher than that of uninoculated willows, respectively. The qPCR analysis showed that the expression of vp2 gene in the microorganism-inoculated willow leaves was always higher than that in willow alone. The expression of vp2 gene in P. cinerea XC-inoculated willow cuttings was 270.81% higher than that in uninoculated willows. Further observation of the ultrastructure of root cells under salt stress revealed that most of the vesicles in the root tip cells of willow were intact and secreted phagocytic vesicles to absorb sodium ions in the cytoplasm. This study shows that the combined beneficial fungi and rhizosphere-promoting bacteria inoculation technology as a practical biotechnological approach to enhance the growth of willows in salt-affected soils.

Applications and immobilization strategies of the copper-centred laccase enzyme; a review

Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.

Yellow laccase produced by Trametes versicolor K1 on tomato waste: A comparative study with the blue one produced on semi-synthetic medium

Laccase production by fungal growth on agrifood waste is still poorly studied. Trametes versicolor K1 isolated from palm bark produced a yellow non glycosylated laccase from tomato waste based medium (TMT) and a blue glycosylated laccase on glucose medium (GLU). Lignocellulosic biomass, such as pinecones (PIN), palm leaves (PLM), olive pomace (OLV), and alfa stems (ALF) have also been used as growth medium for T. versicolor K1. In these conditions, very low or no laccase production was observed. When peptone was supplied in TMT medium, the laccase activity increased from 4170 U/L to 8618 U/L. By increasing the culture volume up to 1 L, laccase production on TMT was 9929 U/L. The yellow laccase (TmtLac) was purified from the supernatant TMT medium and has shown similar characteristics with the blue laccase (GluLac) purified from the GLU medium. Their apparent protein size was 63 kDa. Catalytic activities of the yellow form were not very different from those of the blue form, but specific activity of the purified yellow laccase produced on tomato waste was much higher. The K_m and V_m values for four substrates, ABTS, DMP, guaiacol, and pyrogallol were almost similar for both isoenzymes. The optimum pH and temperature were respectively 4.0 and 50 °C. Although the level of glycosylation is clearly different, the thermostability of TmtLac and GluLac are quite similar. TmtLac is even slightly more tolerant at 60 °C for 24 h than GluLac. Moreover TmtLac showed greater stability at alkaline pH after 24 h compared to that of GluLac.We demonstrate that activity of the yellow TmtLac is not significantly affected compared to the blue laccase and that tomato waste is a simple and interesting lignocellulosic substrate to the laccase producer Trametes sp.

Enhanced lignin degradation of paddy straw and pine needle biomass by combinatorial approach of chemical treatment and fungal enzymes for pulp making

Paddy straw (PS) and pine needles (PN) are one of the challenging biomasses in terms of disposal and compost making due to their high silica and tannin contents. Particulate air pollution, loss of biodiversity and respiratory impairments are some of disastrous outcomes caused by burning. However, high percentage of cellulose and hemicellulose makes them potential substrate for paper and pulp industries. The main aim of work was to study and utilize a combinatorial approach of weak chemical treatment and lignin degrading fungal species as agents of effective production of lignin modifying enzymes (LME's) for lignin depolymerisation from the biomasses. Phanerochaete chrysosporium was found to be the best degrader of lignin (47.11 % in PS + PN in 28 days) with maximum LME's production between 10th-17th days. Efficient lignin degradation in the PS and PN biomass will aid further application in pulp production supporting the transition to a circular economy in a greener way.

A comparative screening of laccase-mediator systems by white-rot fungi laccases for biocatalytic benzyl alcohol oxidation

Production of value-added compounds from waste materials is of utmost importance for the development of a sustainable society especially regarding their use as catalysts in industrially relevant synthetic reactions. Herein, we show the production of laccases from four white-rot fungi, which were grown on agricultural residues, specifically Trametes versicolor 11269, Pleurotus ostreatus 1020, Panus tigrinus 707 and Lentinula edodes SC-495. The produced laccases were tested on a laccase-mediator system (LMS) for the biocatalytic oxidation of the model substrate benzyl alcohol into benzaldehyde. The LMS was carried out in the presence both of tetrahydrofuran as co-solvent and of the mediator 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) due to its high redox potential and its ability to perform the oxidation. Tolerance studies showed that the dialyzed solutions were able to tolerate 1% (99:1 v/v) of co-solvent, whereas a concentration of 10% v/v had a detrimental activity. Performances in the biocatalytic oxidation of laccase solutions from different purification steps were compared. Similar conversion was observed for laccase in dialysis (raw) and gel filtration (GF) product versus commercial T. versicolor laccase. The latter oxidized almost 99% of substrate while the other laccase solutions were able to reach a conversion from 91% for the laccase solution from P. tigrinus 707 after dialysis, to 50% for the laccase solution from P. ostreatus 1020 after gel filtration. This work highlights the potential of unpurified laccase solutions to be used as catalysts in synthetic reactions.

Ligninolytic characteristics of Pleurotus ostreatus cultivated in cotton stalk media

Biodelignification is widely regarded as a low-efficiency process because it is usually slow and difficult to control. To improve its efficiency and understand its mechanism, the present study analyzed the delignification characteristics of Pleurotus ostreatus grown on a cotton stalk medium. The results demonstrated that all strains of P. ostreatus can selectively degrade the cotton stalk lignin. When cultured in a cotton stalk medium for 60 days, P. ostreatus degraded lignin primarily during its mycelium growth with up to 54.04% lignin degradation and produced laccase and manganese dependent peroxidase with high activity levels at the peaks of 70.17 U/ml and 62.39 U/ml, respectively, but no detectable lignin peroxidase. The results of nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy analyses of significant changes in lignin structure revealed that syringyl (S) lignin units were more degraded than guaiacyl (G) lignin units, with a significantly elevated G/S ratio. The Gas Chromatography-Mass Spectrometer analysis of low-molecular-weight compounds revealed that the delignification resulted in the formation of alcohols, organic acids, benzodiazepines, and alkanes. Identified benzodiazepines implied the degradation of G and S units of lignin. These findings will help to improve the efficiency of biodelignification and expand our understanding of its mechanism.

Laccase production by Pleurotus ostreatus using cassava waste and its application in remediation of phenolic and polycyclic aromatic hydrocarbon-contaminated lignocellulosic biorefinery wastewater

The treatment of contaminants from lignocellulosic biorefinery effluent has recently been identified as a unique challenge. This study focuses on removing phenolic contaminants and polycyclic aromatic hydrocarbons (PAHs) from lignocellulosic biorefinery wastewater (BRW) applying a laccase-assisted approach. Cassava waste was used as a substrate to produce the maximum yield of laccase enzyme (3.9 U/g) from Pleurotus ostreatus. Among the different inducers supplemented, CuSO₄ (0.5 mM) showed an eight-fold increase in enzyme production (30.8 U/g) after 240 h of incubation. The catalytic efficiency of laccase was observed as 128.7 ± 8.47 S^-1mM^-1 for syringaldazine oxidation at optimum pH 4.0 and 40 °C. Laccase activity was completely inhibited by lead (II) ion, mercury (II) ion, sodium dodecyl sulphate, sodium azide and 1,4 dithiothretiol and induced significantly by manganese (II) ion and rhamnolipid. After treating BRW with laccase, the concentrations of PAHs and phenolic contaminants of 1144 μg/L and 46160 μg/L were reduced to 96 μg/L and 16100 μg/L, respectively. The ability of laccase to effectively degrade PAHs in the presence of different phenolic compounds implies that phenolic contaminants may play a role in PAHs degradation. After 240 h, organic contaminants were removed from BRW in the following order: phenol >2,4-dinitrophenol > 2-methyl-4,6-dinitrophenol > 2,3,4,6-tetrachlorophenol > acenaphthene > fluorine > phenanthrene > fluoranthene > pyrene > anthracene > chrysene > naphthalene > benzo(a)anthracene > benzo(a)pyrene > benzo(b)fluoranthene > pentachlorophenol > indeno(1,2,3-cd)pyrene > benzo(j) fluoranthene > benzo[k]fluoranthène. The multiple contaminant remediation from the BRW by enzymatic method, clearly suggests that the laccase can be used as a bioremediation tool for the treatment of wastewater from various industries.

Organic waste recycling for carbon smart circular bioeconomy and sustainable development: A review

The development of sustainable and low carbon impact processes for a suitable management of waste and by-products coming from different factors of the industrial value chain like agricultural, forestry and food processing industries. Implementing this will helps to avoid the negative environmental impact and global warming. The application of the circular bioeconomy (CB) and the circular economic models have been shown to be a great opportunity for facing the waste and by-products issues by bringing sustainable processing systems which allow to the value chains be more responsible and resilient. In addition, biorefinery approach coupled to CB context could offer different solution and insights to conquer the current challenges related to decrease the fossil fuel dependency as well as increase efficiency of resource recovery and processing cost of the industrial residues. It is worth to remark the important role that the biotechnological processes such as fermentative, digestive and enzymatic conversions play for an effective waste management and carbon neutrality.

Microaerobic conditions enhance laccase production from Rheinheimera sp. in an economical medium

Statistical optimization of aeration conditions viz. aerobic, microaerobic and anaerobic, was performed using response surface methodology (RSM) utilizing soybean meal as medium to enhance the production of laccase from Rheinheimera sp. Maximum laccase yield (18.48 × 10⁵ U/L) was obtained under microaerobic (static) conditions sustained for 12 h in tandem with 26 h aerobically (150 rpm) grown culture, which was 17.03-fold higher than laccase production in the starting M162 medium under aerobic conditions (150 rpm). The reduction in incubation time from 72 to 38 h and utilization of cost-effective soybean meal as medium, which is easily available from local market, have provided a promising, eco-friendly method of laccase enzyme production. Enhanced expression of laccase gene under microaerobic conditions corresponded to the increased expression of fnr (fumarate nitrate reductase) gene, the oxygen sensing global regulator. The putative FNR-binding site upstream of laccase transcription initiation site was predicted to play an imperative role in Rheinheimera sp. adaptation from aerobic to microaerobic conditions and for enhanced laccase production.

A systematic review on potential microbial carbohydrases: current and future perspectives

Various studies have shown that the microbial proteins are often more stable than belongs to other sources like plant and animal origin. Hence, the interest in microbial enzymes has gained much attention due to many potential applications like bioenergy, biofuel production, biobleaching, bioconversion and so on. Additionally, recent trends revealed that the interest in isolating novel microbes from harsh environments have been the main focus of many scientists for various applications. Basically, industrially important enzymes can be categorized into mainly three groups: carbohydrases, proteases, and lipases. Among those, the enzymes especially carbohydrases involved in production of sugars. Carbohydrases include amylases, xylanases, pectinases, cellulases, chitinases, mannases, laccases, ligninases, lactase, glucanase, and glucose oxidase. Thus, here, an approach has been made to highlight five enzymes namely amylase, cellulase, laccase, pectinase, and xylanase from different sources with special emphasis on their properties, mechanism, applications, production optimization, purification, molecular approaches for its enhanced and stable production, and also biotechnological perspectives of its future development. Also, green and sustainable catalytic conversion strategies using nanoparticles of these enzymes have also been discussed. This review will provide insight into the carbohydrases importance and their usefulness that will help to the researchers working in this field.

Green production of a yellow laccase by Coriolopsis gallica for phenolic pollutants removal

As a group of green biocatalysts, fungal laccases have aroused great interest in diverse biotechnological fields. Therein, yellow laccase has advantages over blue laccase in catalytic performance, but it is not common in the reported fungal laccases. Here, we report a yellow laccase from white-rot fungus Coriolopsis gallica NCULAC F1 about its production, purification, characterization, and application. Laccase production in the co-fermentation of pomelo peel and wheat bran reached the enzyme activity by 10,690 U/L after 5 days with a 13.58-time increase. After three steps of purification, laccase increased the specific activity from 30.78 to 188.79 U/mg protein with an activity recovery of 45.64%. The purified C. gallica laccase (CGLac) showed a molecular mass of about 57 kDa. CGLac had a yellow color and no absorption peaks at 610 nm and 330 nm, suggesting that it’s a yellow laccase. CGLac exhibited stability towards temperature (40–60 °C) and neutral pH (6.0–8.0). Fe³⁺ and Mn²⁺ strongly stimulated CGLac activity by 162.56% and 226.05%, respectively. CGLac remained high activities when exposed to organic reagents and putative inhibitors. Additionally, CGLac contributed to 90.78%, 93.26%, and 99.66% removal of phenol, p-chlorophenol and bisphenol A after 120 min, respectively. In conclusion, a green efficient production strategy was introduced for fungal laccase, and the obtained CGLac presented great enzymatic properties and catalytic potential in the removal of phenolic pollutants.

Pomelo peels and wheat bran are great nutritional sources and laccase inducers.

CGLac showed the spectral characteristic of yellow laccase.

CGLac had great stability and catalytic ability for phenolic pollutants removal.

Production and properties of a laccase isozyme (FvLcc3) from the edible mushroom Flammulina velutipes, which is undetectable under the culture condition for fruiting body formation

Extracellular laccase isozyme (FvLcc3) from the edible mushroom Flammulina velutipes was found to be undetectable under the culture condition for fruiting body formation. FvLcc3 was purified and determined to be an approximately 53-kDa monomeric protein. FvLcc3 showed the highest catalytic efficiency (kcat/Km) toward 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) followed by 2,6-dimethoxyphenol and guaiacol and did not oxidize 3,4-dihydroxy-l-phenylalanine and l-tyrosine.

Establishment of an Efficient Polyethylene Glycol (PEG)-Mediated Transformation System in Pleurotus eryngii var. ferulae Using Comprehensive Optimization and Multiple Endogenous Promoters

Pleurotus eryngii var. ferulae, a fungus of the genus Pleurotus, efficiently degrades lignin, especially during co-cultivation with other fungi. However, low transformation efficiency and heterologous gene expression restrict systematic studies of the molecular mechanisms and metabolic control of natural products in this mushroom. In this study, the homologous resistance marker carboxin (cbx) was used to establish a polyethylene glycol-mediated transformation (PMT) system in P. eryngii var. ferulae. Optimization of the transformation process greatly improved the number of positive transformants. In particular, we optimized: (i) protoplast preparation and regeneration; (ii) screening methods; and (iii) transformation-promoting factors. The optimized transformation efficiency reached 72.7 CFU/μg, which is higher than the average level of Pleurotus sp. (10–40 CFU/μg). Moreover, three endogenous promoters (Ppfgpd1, Ppfgpd2, and Ppfsar1) were screened and evaluated for different transcription initiation characteristics. A controllable overexpression system was established using these three promoters that satisfied various heterologous gene expression requirements, such as strong or weak, varied, or stable expression levels. This study lays the foundation for recombinant protein expression in P. eryngii var. ferulae and provides a method to investigate the underlying molecular mechanisms and secondary metabolic pathway modifications.

Laccase-Driven Transformation of High Priority Pesticides Without Redox Mediators: Towards Bioremediation of Contaminated Wastewaters

In this study, Pleurotus dryinus was grown on municipal biosolids (BS) as the substrate to produce laccase for the removal of pesticides (fungicides, herbicides, and insecticides) from wastewater. Among the various types of BS tested, sterilized biosolids were the most promising substrate for laccase production by P. dryinus with a maximal laccase activity (162.1 ± 21.1 U/g dry substrate), followed by hygenized biosolids (96.7 ± 17.6 U/g dry substrate), unsterilized biosolids (UBS) (31.9 ± 1.2 U/g dry substrate), and alkali-treated biosolids (8.2 ± 0.4 U/g dry substrate). The ultrasound-assisted extraction of this enzyme from fermented UBS was carried out with 0.1 M phosphate buffer at pH 7.0, which increased the enzyme activity of the crude extract by 30%. To test the catalytic potential of the biocatalyst in real matrices, 1 U/ml of recovered crude laccase extract was applied for 24 h for the removal of 29 pesticides (nine fungicides, 10 herbicides, and 10 insecticides) either separately or as a mixture from spiked biologically treated wastewater effluent. When treated with crude enzyme extract, high-priority herbicides metolachlor and atrazine were completely removed, while 93%–97% of the insecticides aldicarb, spinosad, and azinphos-methyl and up to 91% of kresoxim-methyl were removed. Promising results were obtained with BS-derived crude enzyme extract exhibiting improved pesticides removal, which may be due to the mediator effect resulting from the catalytic transformation of other molecules in the cocktail. The results demonstrated a promising integrated bioprocess for the removal of pesticides in wastewater using crude laccase obtained from BS.

Biodelignification of lignocellulose using ligninolytic enzymes from white-rot fungi

Lignocellulose is the most abundant biomass available on earth, including wood and agricultural wastes such as rice straw, corn cobs, and oil palm empty bunches. The biopolymer content in lignocellulose has a great potential as feedstock for producing industrial raw materials such as glucose, sorbitol, xylose, xylitol, and other pharmaceutical excipients. Currently, scientists and governments agree that the enzymatic delignification method is an environmentally friendly green method to be applied. This review attempts to explain the proper preparation of the enzymes laccase, lignin peroxidase, and manganese peroxidase, as well as the important factors influencing their activity. The recent applications of the enzymes for detoxification of hazardous substances, proper enzyme immobilization technique, and future prospect combination with DESs extraction of lignin are also discussed.

Production of fungal laccase on pineapple waste and application in detoxification of malachite green

The main purpose of this work was to use pineapple crowns as substrate for optimizing laccase production by Trametes versicolor in lab-scale experiments. One-factor-at-the-time analysis and response surface methodology were used to optimize production. A single laccase with molecular weight of 45 kDa was the main protein produced. A maximal laccase activity of 60.73 ± 1.01 U/g was obtained in 7-day cultures, representing a 6.7-fold increase compared to non-optimized conditions. The optimized conditions were temperature: 28 °C; initial moisture: 90%; glucose: 8.38%; yeast extract: 2.86%. Combining activity and stability, the best conditions for using this laccase during the long periods required by large-scale processes are pH 4.0-5.0 and temperature of 40-50 °C. Under these conditions, the crude laccase was efficient in detoxifying the dye malachite green with a K_M of 14.33 ± 1.94 µM and a V_max of 0.482 ± 0.029 µM/min with 0.1 units/mL. It can be concluded that pineapple crown leaves can be effectively used as substrate by T. versicolor for producing laccase under solid-state culture conditions. Laccase is an industrially relevant enzyme and its production with concomitant valorization of pineapple crowns as substrate offers highly interesting perspectives.

The production of laccases by white-rot fungi under solid-state fermentation conditions

Laccases (E.C. 1.10.3.2) produced by white-rot fungi (WRF) can be widely used, but the high cost prevents their use in large-scale industrial processes. Finding a solution to the problem could involve laccase production by solid-state fermentation (SSF) simulating the natural growth conditions for WRF. SSF offers several advantages over conventional submerged fermentation (SmF), such as higher efficiency and productivity of the process and pollution reduction. The aim of this review is therefore to provide an overview of the current state of knowledge about the laccase production by WRF under SSF conditions. The focus is on variations in the up-stream process, fermentation and down-stream process and their impact on laccase activity. The variations of up-stream processing involve inoculum preparation, inoculation of the medium and formulation of the propagation and production media. According to the studies, the production process can be shortened to 5-7 days by the selection of a suitable combination of lignocellulosic material and laccase producer without the need for any additional components of the culture medium. Efficient laccase production was achieved by valorisation of wastes as agro-food, municipal wastes or waste generated from wood processing industries. This leads to a reduction of costs and an increase in competitiveness compared to other commonly used methods and/or procedures. There will be significant challenges and opportunities in the future, where SSF could become more efficient and bring the enzyme production to a higher level, especially in new biorefineries, bioreactors and biomolecular/genetic engineering.

Laccases as green and versatile biocatalysts: from lab to enzyme market-an overview

Laccases are multi-copper oxidase enzymes that catalyze the oxidation of different compounds (phenolics and non-phenolics). The scientific literature on laccases is quite extensive, including many basic and applied research about the structure, functions, mechanism of action and a variety of biotechnological applications of these versatile enzymes. Laccases can be used in various industries/sectors, from the environmental field to the cosmetics industry, including food processing and the textile industry (dyes biodegradation and synthesis). Known as eco-friendly or green enzymes, the application of laccases in biocatalytic processes represents a promising sustainable alternative to conventional methods. Due to the advantages granted by enzyme immobilization, publications on immobilized laccases increased substantially in recent years. Many patents related to the use of laccases are available, however, the real industrial or environmental use of laccases is still challenged by cost-benefit, especially concerning the feasibility of producing this enzyme on a large scale. Although this is a compelling point and the enzyme market is heated, articles on the production and application of laccases usually neglect the economic assessment of the processes. In this review, we present a description of laccases structure and mechanisms of action including the different sources (fungi, bacteria, and plants) for laccases production and tools for laccases evolution and prediction of potential substrates. In addition, we both compare approaches for scaling-up processes with an emphasis on cost reduction and productivity and critically review several immobilization methods for laccases. Following the critical view on production and immobilization, we provide a set of applications for free and immobilized laccases based on articles published within the last five years and patents which may guide future strategies for laccase use and commercialization.

Fungal Laccases: The Forefront of Enzymes for Sustainability

Enzymatic catalysis is one of the main pillars of sustainability for industrial production. Enzyme application allows minimization of the use of toxic solvents and to valorize the agro-industrial residues through reuse. In addition, they are safe and energy efficient. Nonetheless, their use in biotechnological processes is still hindered by the cost, stability, and low rate of recycling and reuse. Among the many industrial enzymes, fungal laccases (LCs) are perfect candidates to serve as a biotechnological tool as they are outstanding, versatile catalytic oxidants, only requiring molecular oxygen to function. LCs are able to degrade phenolic components of lignin, allowing them to efficiently reuse the lignocellulosic biomass for the production of enzymes, bioactive compounds, or clean energy, while minimizing the use of chemicals. Therefore, this review aims to give an overview of fungal LC, a promising green and sustainable enzyme, its mechanism of action, advantages, disadvantages, and solutions for its use as a tool to reduce the environmental and economic impact of industrial processes with a particular insight on the reuse of agro-wastes.

Recent Developments in the Immobilization of Laccase on Carbonaceous Supports for Environmental Applications - A Critical Review

Τhe ligninolytic enzyme laccase has proved its potential for environmental applications. However, there is no documented industrial application of free laccase due to low stability, poor reusability, and high costs. Immobilization has been considered as a powerful technique to enhance laccase's industrial potential. In this technology, appropriate support selection for laccase immobilization is a crucial step since the support could broadly affect the properties of the resulting catalyst system. Through the last decades, a large variety of inorganic, organic, and composite materials have been used in laccase immobilization. Among them, carbon-based materials have been explored as a support candidate for immobilization, due to their properties such as high porosity, high surface area, the existence of functional groups, and their highly aromatic structure. Carbon-based materials have also been used in culture media as supports, sources of nutrients, and inducers, for laccase production. This study aims to review the recent trends in laccase production, immobilization techniques, and essential support properties for enzyme immobilization. More specifically, this review analyzes and presents the significant benefits of carbon-based materials for their key role in laccase production and immobilization.

Enzymatic Pretreatment with Laccases from Lentinus sajor-caju Induces Structural Modification in Lignin and Enhances the Digestibility of Tropical Forage Grass (Panicum maximum) Grown under Future Climate Conditions

Since laccase acts specifically in lignin, the major contributor to biomass recalcitrance, this biocatalyst represents an important alternative to the pretreatment of lignocellulosic biomass. Therefore, this study investigates the laccase pretreatment and climate change effects on the hydrolytic performance of Panicum maximum. Through a Trop-T-FACE system, P. maximum grew under current (Control (C)) and future climate conditions: elevated temperature (2 °C more than the ambient canopy temperature) combined with elevated atmospheric CO₂ concentration(600 μmol mol⁻¹), name as eT+eC. Pretreatment using a laccase-rich crude extract from Lentinus sajor caju was optimized through statistical strategies, resulting in an increase in the sugar yield of P. maximum biomass (up to 57%) comparing to non-treated biomass and enabling hydrolysis at higher solid loading, achieving up to 26 g L⁻¹. These increments are related to lignin removal (up to 46%) and lignin hydrophilization catalyzed by laccase. Results from SEM, CLSM, FTIR, and GC-MS supported the laccase-catalyzed lignin removal. Moreover, laccase mitigates climate effects, and no significant differences in hydrolytic potential were found between C and eT+eC groups. This study shows that crude laccase pretreatment is a potential and sustainable method for biorefinery solutions and helped establish P. maximum as a promising energy crop.

Bio-Delignification of Green Waste (GW) in Co-Digestion with the Organic Fraction of Municipal Solid Waste (OFMSW) to Enhance Biogas Production

The organic fraction of municipal solid waste (OFMSW) is recognized as a suitable substrate for the anaerobic digestion (AD) process and is currently considered a mature technology. A promising strategy to enhance biogas yield and productivity is the co-digestion of OFMSW with other organic biomass, such as green waste (GW), a mixture of leaves, grass, and woody materials originated from private yards and public greenspace management. The main limitation to the use of GW for biogas production is the high percentage of the lignocellulosic fraction, which makes necessary a pretreatment of delignification to dissolve the recalcitrant structure. In this study, a new strategy of sustainable bio-delignification using the white-rot fungi Bjerkandera adusta (BA) in comparison with other chemical pretreatments were investigated. Untreated and treated GW were, respectively, submitted to anaerobic co-digestion with OFMSW. AD processes were carried out in a lab-scale plant for 30 days in thermophilic conditions (55 °C). Biogas cumulative production was increased by about 100% in the case of treated GW compared with that of just OFMSW, from 145 to 289 Nm3 CH4/ton SV, and productivity almost doubled from 145 to 283 Nm3/ton FM * day. The measured average methane content values in the cumulative biogas were 55% from OFMSW and 54% from GW. Moreover, over 95% of the biogas was produced in 20 days, showing the potential opportunity to reduce the AD time.

Evaluation of Laccase Activities by Three Newly Isolated Fungal Species in Submerged Fermentation With Single or Mixed Lignocellulosic Wastes

Three newly isolated fungal species, namely, Cerrena unicolor Han 849, Lenzites betulina Han 851, and Schizophyllum commune Han 881, isolated from their native habitats in Wulingshan National Nature Reserve of Hebei Province of northern China, were screened for laccase production with single or mixed lignocellulosic wastes. C. unicolor Han 849 was found to express the highest levels of laccase with single or mixed lignocellulosic wastes compared with L. betulina Han 851 and S. commune Han 881. The highest laccase activity from the mixed fungal culture of C. unicolor Han 849 and S. commune Han 881 or L. betulina Han 851 on Firmiana platanifolia was 1,373.12 ± 55.93 and 1,144.85 ± 34.97 U/L, respectively, higher than that from other tested conditions. L. betulina Han 851 or S. commune Han 881 mixed with other species was also helpful for accelerating laccase secretion due to reach maximum enzyme activity quickly. The treatment of mixing different species, including the mixture of two or three species, was obviously conducive to the improvement of laccase activity on Firmiana platanifolia. These results revealed that the fungal co-culture and the mixed lignocellulosic wastes contribute to the improvement of laccase activities and enhance laccase activities within a short period. These findings would be helpful for providing a new method for rapid production of low-cost laccase and for optimization of integrated industrial laccase production.

Trametes versicolor in lignocellulose-based bioeconomy: State of the art, challenges and opportunities

Although Trametes versicolor is one of the most investigated white-rot fungi, the industrial application of this fungus and its metabolites is still far from reaching its full potential. This review aims to highlight the opportunities and challenges for the industrial use of T. versicolor according to the principles of circular bioeconomy. The use of this fungus can contribute significantly to the success of efforts to valorize lignocellulosic waste biomass and industrial lignocellulosic byproducts. Various techniques of T. versicolor cultivation for enzyme production, food and feed production, wastewater treatment, and biofuel production are listed and critically evaluated, highlighting bottlenecks and future perspectives. Applications of T. versicolor crude laccase extracts in wastewater treatment, removal of lignin from lignocellulose, and in various biotransformations are analyzed separately.

An insight into transcriptome of Cyathus bulleri for lignocellulase expression on wheat bran

To identify enzymes that can be effectively used for hydrolysis of lignocellulosic biomass, an attractive carbon source in biorefineries, transcriptome analysis was carried out of wheat bran grown fungus, Cyathus bulleri. A comprehensive set of transcripts, encoding carbohydrate active enzymes, were identified. These belonged to 55, 32, 12, 11 and 7 different families of the enzyme classes of Glycoside Hydrolases (GHs), Glycosyl Transferases (GTs), Auxiliary Activities (AAs), Carbohydrate Esterases (CEs) and Polysaccharide Lyases (PLs) respectively. Higher levels of transcripts were obtained for proteins encoding cellulose and hemicellulose degrading activities (of the GH class) with the highest diversity found in the transcripts encoding the hemicellulases. Several transcripts encoding pectin degrading activity were also identified indicating close association of the pectin with the cellulose/hemicellulose in the cell wall of this fungus. Transcripts encoding ligninases were categorized into Cu radical oxidase, Glucose-Methanol-Choline oxidoreductase (with 37 different transcripts in the AA3 sub-family), Laccase and Manganese peroxidases. Temporal gene expression profile for laccase isoforms was studied to understand their role in lignin degradation. To our knowledge, this is the first analysis of the transcriptome of a member belonging to the family Nidulariaceae.

Removal of pharmaceuticals and personal care products using native fungal enzymes extracted during the ligninolytic process

Significant concentrations of pharmaceuticals and personal care products (PPCPs) have been detected in aquatic environment. Fungal enzymatic processes can oxidize these persistent PPCPs; thus, these processes have attracted considerable attention from the scientific community. Here, we evaluated the efficacy of the removal of PPCPs using native fungal enzymes derived from Bjerkandera spp. TBB-03 under various conditions. Among the eight lignocellulosic substrates, ash, which showed the highest laccase production, was selected as the sole enzyme inducer. TBB-03 laccase was found to exhibit remarkable stability under varied pH and temperature conditions. Acetaminophen and bisphenol A were effectively removed by TBB-03 laccase under various conditions, except at pH 8. Although TBB-03 laccase could not efficiently remove single-state sulfamethoxazole directly, a 22% of improvement in sulfamethoxazole removal was observed in the presence of acetaminophen. Overall, our proposed approach showed that Bjerkandera adusta TBB-03 can be potentially applied for further research regarding PPCP remediation.

Growth of Leucoagaricus gongylophorus Möller (Singer) and production of key enzymes in submerged and solid-state cultures with lignocellulosic substrates

The aim of this study was to characterize the growth of the fungus Leucoagaricus gongylophorus LEU18496, isolated from the fungus garden of the nest of leaf cutter ants Atta mexicana. The fungus garden was cultivated in an artificial laboratory nest and the fungus further grown in submerged (SmC) and solid state (SSC) cultures with sugarcane bagasse, grass or model substrates containing CM-cellulose, xylan or lignin. The CO₂ production rate with grass in SmC (Vmax 34.76 mg CO₂ L_gas^-1 day^- 1) was almost four times than SSC (Vmax 9.49 mg CO₂ L_gas^-1 day^- 1), while the production rate obtained in sugarcane bagasse in SmC (Vmax 16.02 mg CO₂ L_gas^-1 day^- 1) was almost three times than that for SSC (Vmax 5.42 mg CO₂ L_gas^-1 day^- 1). In addition, the fungus grew with defined carbon substrates mixtures in SmC, but at different rates, first xylan, followed by CM-cellulose and lignin. Endoglucanase and xylanase activities (U mg_protein^-1) were detected in all cultures, the specific activity was higher in the fungus-garden, 5.2 and 1.8; followed by SSC-grass, 1.5 and 0.8, and SSC-bagasse, 0.9 and 0.8, respectively. Laccase activity in the fungus-garden was 44.8 U L^- 1 and 10.9 U L^- 1 in the SSC-grass. The gongylidia structures observed by environmental scanning electron microscopy were ca. 40 µm and the hyphae width ca. 5 µm. The results show that L. gongylophorus from A. mexicana have promising applications for the treatment of plant residues to release fermentable sugars and the production of high value lignocellulolytic enzymes such as endoglucanase, xylanase or laccases.

Multiplexed CRISPR/Cas9-Mediated Knockout of Laccase Genes in Salvia miltiorrhiza Revealed Their Roles in Growth, Development, and Metabolism

Laccases are multicopper-containing glycoproteins related to monolignol oxidation and polymerization. These properties indicate that laccases may be involved in the formation of important medicinal phenolic acid compounds in Salvia miltiorrhiza such as salvianolic acid B (SAB), which is used for cardiovascular disease treatment. To date, 29 laccases have been found in S. miltiorrhiza (SmLACs), and some of which (SmLAC7 and SmLAC20) have been reported to influence the synthesis of phenolic acids. Because of the functional redundancy of laccase genes, their roles in S. miltiorrhiza are poorly understood. In this study, the CRISPR/Cas9 system was used for targeting conserved domains to knockout multiple genes of laccase family in S. miltiorrhiza. The expressions of target laccase genes as well as the phenolic acid biosynthesis key genes decrease dramatically in editing lines. Additionally, the growth and development of hairy roots was significantly retarded in the gene-edited lines. The cross-sections examination of laccase mutant hairy roots showed that the root development was abnormal and the xylem cells in the edited lines became larger and looser than those in the wild type. Additionally, the accumulation of RA as well as SAB was decreased, and the lignin content was nearly undetectable. It suggested that SmLACs play key roles in development and lignin formation in the root of S. miltiorrhiza and they are necessary for phenolic acids biosynthesis.

Bioprocessing of Agricultural Residues as Substrates and Optimal Conditions for Phytase Production of Chestnut Mushroom, Pholiota adiposa, in Solid State Fermentation

Phytase is an enzyme that breaks down phytates to release phosphorus in an available form. This enzyme plays an important role in animals, especially monogastric animals. It serves to improve phytate digestion along with phosphorus absorption, which are required for optimal growth performance and health. In this study, five mushroom species (Amauroderma rugosum SDBR-CMU-A83, Ganoderma mastoporum SDBR-CMU-NK0244, Marusmius sp.1 SDBR-CMU-NK0215, Pholiota adiposa SDBR-CMU-R32 and Piptoporellus triqueter SDBR-CMU-P234) out of 27 mushroom species displayed positive phytase production by agar plate assay. Consequently, these five mushroom species were selected for determination of their potential ability to produce phytase under solid-state fermentation using five agricultural residues (coffee parchment, oil palm empty fruit bunches, rice bran, sawdust, and water hyacinth) as substrates. The highest yield of phytase production (17.02 ± 0.92 units/gram dry substrate) was obtained after one week of fermentation. Optimization for phytase production was determined by statistical approaches using a Plackett-Burman design to screen ten parameters of relevant substrate components. Two significant parameters, the amount of water hyacinth and the moisture content, were found to affect the production process of phytase. Furthermore, the optimal temperature, pH value, and fermentation period were evaluated. The results indicated that the highest degree of phytase production at 53.66 ± 1.68 units/gram dry substrate (3.15-fold increase) was obtained in water hyacinth containing 85% moisture content by addition with a suitable basal liquid medium at a pH value of 6.5 after being incubated at 30 °C for seven days. The crude phytase of P. adiposa was precipitated and the precipitated extract was then used to determine partial characterizations. The precipitated extract displayed high activities after exposure to conditions of 42 °C and pH 5.0. Furthermore, Fe²⁺ enhanced phytase activity and precipitated extract displayed the best stability at a pH value of 8.0 and a temperature of 4 °C.

Isolation, identification and optimization of enhanced production of laccase from Galactomyces geotrichum under solid-state fermentation

Laccases are a group of oxidases that catalyze the oxidation of a wide range of electron rich substrates like phenolic compounds, lignin and aromatic amines. They are of interest because of their potential to be used in environmental and industrial applications. In this research, potent laccase producer fungi were screened and isolated from olive mill wastewater (OMW). One of the 23 isolated fungi was identified as Galactomyces geotrichum based on 18S rDNA sequence analysis that detected good laccase activity. Produced laccase had a molecular weight of 55 kDa that was confirmed by zymogram analysis. This is the first report about the optimization of laccase Production by G. geotrichum under solid-state fermentation. The optimization was made by the Taguchi design of experiments (DOE) methodology. An orthogonal array (L25) was designed using Minitab 19 software to study four effective process factors in five levels for laccase production. The optimum condition derived was; moisture content (80%), fermentation time (14 day), CuSO₄⋅5H₂O as the inducer (300 μM), glucose as a co-substrate (5 g/L). Maximum laccase activity of 52.86 (U/g of dry substrate) was obtained using optimum fermentation condition. This study aimed to better understand the laccase producing microorganisms in OMW and take them to OMW treatment that is rich in phenolic compounds.

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.

Recent Advances in Applied Microbiology: Editorial

The importance of microbiology has grown exponentially since the development of genomics, transcriptomics, and proteomics, making it possible to clarify microbial biogeochemical processes and their interactions with macroorganisms in both health and disease. Particular attention is being payed to applied microbiology, a discipline that deals with the application of microorganisms to specific endeavors, whose economic value is expected to exceed USD 675.2 billion by 2024. In the Special Issue "Recent Advances in Applied Microbiology", twenty-four papers were published (four reviews and twenty original research papers), covering a wide range of subjects within applied microbiology, including: microbial pathogenesis, the health-promoting properties of microorganisms and their by-products, food conservation, the production of alcoholic beverages, bioremediation and the application of microbiology to several industrial processes.

Immobilization of Laccase on Magnetic Chelator Nanoparticles for Apple Juice Clarification in Magnetically Stabilized Fluidized Bed

The juice clarification, one of the key steps in juice processing, suffers from haze formation that results from residual phenolic compounds. In this study, laccase was immobilized on metal-chelated magnetic silica nanoparticles and used for continuous juice clarification in a magnetically stabilized fluidized bed (MSFB) assisted by alternating magnetic field. Furthermore, a new combination of laccase catalysis and microfiltration was developed for the juice clarification. Immobilized laccase provided high relative activity within broader ranges of pH and temperature compared to the free enzyme. Magnetic immobilized laccase exhibited the best reaction rate of 12.1 μmol g^–1 min^–1 for catechol oxidation under the alternating magnetic field of 400 Hz, 60 Gs. No activity loss occurred in immobilized laccase after 20 h continuous operation of juice treatment in MSFB under an alternating magnetic field. Combined with microfiltration after treatment with immobilized laccase, the color of apple juice was decreased by 33.7%, and the light transmittance was enhanced by 20.2%. Furthermore, only 16.3% of phenolic compounds and 15.1% of antioxidant activity was reduced for apple juice after the clarification. By this combination strategy, the apple juice possessed good freeze–thaw and thermal stability.