Mushroom Ligninolytic Enzymes―Features and Application of Potential Enzymes for Conversion of Lignin into Bio-Based Chemicals and Materials

Mushroom-Mediated Redox Reactions

The application of biocatalysts in organic synthesis has grown significantly in recent years, and both academia and industry are continuously searching for novel biocatalysts capable of performing challenging chemical reactions. Mushrooms are a rich source of ligninolytic and secondary metabolite biosynthetic enzymes, and therefore were considered promising biocatalysts for organic synthesis. This review focuses on the broad utilization potential of mushroom-based biocatalysts and highlights key advances in mushroom-mediated redox reactions. It mainly includes the reduction of ketones and carboxylic acids, hydroxylation of aromatic and aliphatic compounds, epoxidation of olefins, oxidative cleavage of alkenes, and other uncommon reactions catalyzed by the whole cells or purified enzymes of mushroom origin. Overall, a comprehensive overview of the applications of mushrooms as biocatalysts in organic synthesis is provided, which puts this versatile microorganism in the spotlight of further research.

Influence of Drying Temperatures on Color Variation, Phenolic Compounds and Multi-Elemental Composition of Some Culinary- Medicinal Mushrooms

Although mushrooms are widely used for nutraceutical purposes, post-harvest storage is extremely crucial to avoid degradation and quality reduction in fresh mushrooms. Drying treatments are commonly applied in the mushroom industry to extend shelf life. Drying may cause instability of food quality and antioxidant parameters due to unsuitable drying temperatures. Therefore, in this research a common set of temperatures typically used by mushroom growers was applied (50°C, 60°C, 70°C) to Ganoderma lucidum, Lignosus rhinocerus, Auricularia auricula-judae, and Schizophyllum commune to analyze color changes and concentration of elements and phenolic compounds. Mushrooms were chosen based on commonly cultivated species among growers. L. rhinocerus dried at 70°C indicated significantly lower L* (78.90) compared to control (89.94). Element retention in each sample differed depending on the species. The amount of calcium was significantly higher in L. rhinocerus (11,893 mg/kg) and A. auricula-judae (10,941.81 mg/kg) when dried at 60°C. Drying at 70°C resulted in significantly higher magnesium for Sch. commune (13,054.38 mg/kg) and A. auricula-judae (80,56.92 mg/kg). Higher levels of iron and manganese were observed in Sch. commune dried at 70°C (216.54 and 10.02 mg/kg, respectively). Gallic acid had significantly higher retention at 50°C for A. auricula-judae and G. lucidum. Meanwhile, L. rhinocerus and Sch. commune showed significantly higher gallic acid at 60°C. It is evident from these results that temperature does affect the food quality and elemental parameters during the drying process for each mushroom.

Structural insights, biocatalytic characteristics, and application prospects of lignin-modifying enzymes for sustainable biotechnology-A review

Lignin modifying enzymes (LMEs) have gained widespread recognition in depolymerization of lignin polymers by oxidative cleavage. LMEs are a robust class of biocatalysts that include lignin peroxidase (LiP), manganese peroxidase (MnP), versatile peroxidase (VP), laccase (LAC), and dye-decolorizing peroxidase (DyP). Members of the LMEs family act on phenolic, non-phenolic substrates and have been widely researched for valorization of lignin, oxidative cleavage of xenobiotics and phenolics. LMEs implementation in the biotechnological and industrial sectors has sparked significant attention, although its potential future applications remain underexploited. To understand the mechanism of LMEs in sustainable pollution mitigation, several studies have been undertaken to assess the feasibility of LMEs in correlating to diverse pollutants for binding and intermolecular interactions at the molecular level. However, further investigation is required to fully comprehend the underlying mechanism. In this review we presented the key structural and functional features of LMEs, including the computational aspects, as well as the advanced applications in biotechnology and industrial research. Furthermore, concluding remarks and a look ahead, the use of LMEs coupled with computational frameworks, built upon artificial intelligence (AI) and machine learning (ML), has been emphasized as a recent milestone in environmental research.

Biocatalytic characterization of Hericium erinaceus laccase isoenzymes for the oxidation of lignin derivative substrates

Mushroom laccases are biocatalysts that oxidize various substrates. To identify a novel enzyme involved in lignin valorization, we isolated and characterized laccase isoenzymes from the mushroom Hericium erinaceus. The laccase cDNAs (Lac1a and Lac1b) cloned from the mushroom mycelia consisted of 1536 bp and each encoded a protein with 511 amino acids, containing a 21-amino-acid signal peptide. Comparative phylogenetic analysis revealed high homology between the deduced amino acid sequences of Lac1a and Lac1b and those from basidiomycetous fungi. In the Pichia pastoris expression system, high extracellular production of Lac1a, a glycoprotein, was achieved, whereas Lac1b was not expressed as a secreted protein because of hyper-glycosylation. Biochemical characterization of the purified recombinant Lac1a (rLac1a) protein revealed its oxidizing efficacy toward 14 aromatic substrates. The highly substrate-specific rLac1a showed catalytic efficiencies of 877 s^-1 mM^-1, 829 s^-1 mM^-1, 520 s^-1 mM^-1, and 467 s^-1 mM^-1 toward 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid), hydroquinone, guaiacol, and 2,6-dimethylphenol, respectively. Moreover, rLac1a showed approximately 10 % higher activity in non-ionic detergents and >50 % higher residual activity in various organic solvents. These results indicate that rLac1a is a novel oxidase biocatalyst for the bioconversion of lignin into value-added products.

Vital Conditions to Remove Pollutants from Synthetic Wastewater Using Malaysian Ganoderma lucidum

Mycoremediation, a fungal-based technology, has seen tremendous growth as an effective alternative to treat industrial wastewater due to its ability to oxidise pollutant loadings. Considering the non-toxic properties and high potential degradation performance of Ganoderma lucidum, this research aims to study the performance of a Malaysian G. lucidum strain, the effect of agitation speed, and different carbon-to-nitrogen (C/N) ratio concentrations of synthetic wastewater in degrading chemical oxygen demand (COD) and ammonia. Different agitation speeds (25 rpm, 50 rpm and 100 rpm) and C/N ratios (C10N1, C13.3N1 and C16.7N1) were chosen as parameters to be analysed in this study. The best degradation of COD and ammonia with a percentage removal in the range of 95% to 100% within 30 h of treatment. ANOVA analysis was done using the response surface methodology to verify the obtained results, and it was found that mycoremediation using 100 rpm agitation provided the best results, removing more than 95% of COD and ammonia from synthetic wastewater. The microscopic analysis also showed that the structure of G. lucidum changed after wastewater treatment. This result proved that the Malaysian G. lucidum strain has a good potential in treating synthetic domestic wastewater, especially with high organic content, as a naturally sustainable bioremediation system.

Contemporary proteomic research on lignocellulosic enzymes and enzymolysis: A review

This review overviewed the current researches on the isolation of novel strains, the development of novel identification protocols, the key enzymes and their synergistic interactions with other functional enzyme systems, and the strategies for enhancing enzymolysis efficiencies. The main obstacle for realizing biorefinery of lignocellulosic biomass to biofuels or biochemicals is the high cost of enzymolysis stage. Therefore, research prospects to reduce the costs for lignocellulose hydrolysis were outlined.

Inhibitory Potential of New Phenolic Hydrazide-Hydrazones with a Decoy Substrate Fragment towards Laccase from a Phytopathogenic Fungus: SAR and Molecular Docking Studies

Laccase from pathogenic fungi participates in both the delignification and neutralization of phytoantibiotics. Furthermore, it interferes with the hormone signaling in plants and catalyzes melanization. Infections of these pathogens contribute to loss in forestry, agriculture, and horticulture. As there is still a need to expand knowledge on efficient defense strategies against phytopathogenic fungi, the present study aimed to reveal more information on the molecular mechanisms of laccase inhibition with natural and natural-like carboxylic acid semi-synthetic derivatives. A set of hydrazide-hydrazones derived from carboxylic acids, generally including electron-rich arene units that serve as a decoy substrate, was synthesized and tested with laccase from Trametes versicolor. The classic synthesis of the title inhibitors proceeded with good to almost quantitative yield. Ninety percent of the tested molecules were active in the range of K_I = 8–233 µM and showed different types of action. Such magnitude of inhibition constants qualified the hydrazide-hydrazones as strong laccase inhibitors. Molecular docking studies supporting the experimental data explained the selected derivatives’ interactions with the enzyme. The results are promising in developing new potential antifungal agents mitigating the damage scale in the plant cultivation, gardening, and horticulture sectors.