Heterologous expression and characterization of three laccases obtained from Pleurotus ostreatus HAUCC 162 for removal of environmental pollutants

Optimizing laccase selection for enhanced outcomes: a comprehensive review

Despite their widespread applications in sectors such as pulp and paper, textile, food and beverage, pharmaceuticals, and biofuel production, laccases encounter challenges related to their activity and stability under varying reaction conditions. This review accumulates data on the complex interplay between laccase characteristics and reaction conditions for maximizing their efficacy in diverse biotechnological processes. Benefits of organic media such as improved substrate selectivity and reaction control, and their risks such as enzyme denaturation and reduced activity are reported. Additionally, the effect of reaction conditions such as pH and temperature on laccase activity and stability are gathered and reported. Sources like Bacillus pumilus, Alcaligenes faecalis, Bacillus clausii, and Bacillus tequilensis SN4 are producing laccases that are both thermo-active and alkali-active. Additionally, changes induced by the presence of various substances within reaction media such as metals, inhibitors, and organic solvents are also reported. Bacillus pumilus and Bacillus licheniformis LS04 produce the most resistant laccases in this case. Finally, the remarkable laccases have been highlighted and the proper laccase source for each industrial application is suggested.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04015-5.

Enhanced extracellular production of laccase in Coprinopsis cinerea by silencing chitinase gene

Laccase, a copper-containing polyphenol oxidase, is an important green biocatalyst. In this study, Laccase Lcc5 was homologous recombinantly expressed in Coprinopsis cinerea and a novel strategy of silencing chitinase gene expression was used to enhance recombinant Lcc5 extracellular yield. Two critical chitinase genes, ChiEn1 and ChiE2, were selected by analyzing the transcriptome data of C. cinerea FA2222, and their silent expression was performed by RNA interference (RNAi). It was found that silencing either ChiEn1 or ChiE2 reduced sporulation and growth rate, and increased cell wall sensitivity, but had no significant effect on mycelial branching. Among them, the extracellular laccase activity of the ChiE2-silenced engineered strain Cclcc5-antiChiE2-5 and the control Cclcc5-13 reached the highest values (38.2 and 25.5 U/mL, respectively) at 250 and 150 rpm agitation speeds, corresponding to productivity of 0.35 and 0.19 U/mL·h, respectively, in a 3-L fermenter culture. Moreover, since Cclcc5-antiChiE2-5 could withstand greater shear forces, its extracellular laccase activity was 2.6-fold higher than that of Cclcc5-13 when the agitation speed was all at 250 rpm. To our knowledge, this is the first report of enhanced recombinant laccase production in C. cinerea by silencing the chitinase gene. This study will pave the way for laccase industrial production and accelerate the development of a C. cinerea high-expression system. KEY POINTS: • ChiEn1 and ChiE2 are critical chitinase genes in C. cinerea FA2222 genome. • Chitinase gene silencing enhanced the tolerance of C. cinerea to shear forces. • High homologous production of Lcc5 is achieved by fermentation in a 3-L fermenter.

Theoretical insights into the mechanism underlying aflatoxin B1 transformation by the BsCotA-methyl syringate system

Global concern exists regarding the contamination of food and animal feed with aflatoxin B1 (AFB1), which poses a threat to the health of both humans and animals. Previously, we found that a laccase from Bacillus subtilis (BsCotA) effectively detoxified AFB1 in a reaction mediated by methyl syringate (MS), although the underlying mechanism has not been determined. Therefore, our primary objective of this study was to explore the detoxification mechanism employed by BsCotA. First, the enzyme and mediator dependence of AFB1 transformation were studied using the BsCotA-MS system, which revealed the importance of MS radical formation during the oxidation process. Aflatoxin Q1 (AFQ1) resulting from the direct oxidation of AFB1 by BsCotA, was identified using ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results of UPLC-MS/MS and density functional theory calculations indicated that the products included AFQ1, AFB1-, and AFD1-MS-coupled products in the BsCotA-MS system. The toxicity evaluations revealed that the substances derived from the transformation of AFB1 through the BsCotA-MS mechanism exhibited markedly reduced toxicity compared to AFB1. Finally, we proposed a set of different AFB1-transformation pathways generated by the BsCotA-MS system based on the identified products. These findings greatly enhance the understanding of the AFB1-transformation mechanism of the laccase-mediator system.

Biodegradation strategies of veterinary medicines in the environment: Enzymatic degradation

One Health closely integrates healthy farming, human medicine, and environmental ecology. Due to the ecotoxicity and risk of transmission of drug resistance, veterinary medicines (VMs) are regarded as emerging environmental pollutants. To reduce or mitigate the environmental risk of VMs, developing friendly, safe, and effective removal technologies is an important means of environmental remediation for VMs. Many previous studies have proved that biodegradation has significant advantages in removing VMs, and biodegradation based on enzyme catalysis presents higher operability and specificity. This review focused on biodegradation strategies of environmental pollutants and reviewed the enzymatic degradation of VMs including antimicrobial drugs, insecticides, and disinfectants. We reviewed the sources and catalytic mechanisms of peroxidase, laccase, and organophosphorus hydrolases, and summarized the latest research status of immobilization methods and bioengineering techniques in improving the performance of degrading enzymes. The mechanism of enzymatic degradation for VMs was elucidated in the current research. Suggestions and prospects for researching and developing enzymatic degradation of VMs were also put forward. This review will offer new ideas for the biodegradation of VMs and have a guide significance for the risk mitigation and detoxification of VMs in the environment.

Enzymatic response and antibiotic resistance gene regulation by microbial fuel cells to resist sulfamethoxazole

Microbial fuel cells (MFCs) are a promising and sustainable technology which can generate electricity and treat antibiotic wastewater simultaneously. However, the antibiotic resistance genes (ARGs) induced by antibiotics in MFCs increase risks to ecosystems and human health. In this study, the activities of enzymes and regulation genes related to ARGs in MFCs spiked with sulfamethoxazole (SMX) were evaluated to explore the induction mechanism of ARGs. Under lower doses of SMX (10 mg/L and 20 mg/L SMX in this study), microorganisms tend to up regulate catalase and RpoS regulon to induce sul1, sul3 and intI1. The microorganisms exposed to higher doses of SMX (30 mg/L and 40 mg/L SMX in this study) tend to up regulate superoxide dismutase and SOS response to generate sul2 and sulA. Moreover, the exposure concentrations of SMX had no significant effect on the electricity production of MFCs. This work suggested that the ARGs in MFCs might be inhibited by affecting enzymatic activities and regulatory genes according to the antibiotic concentration without affecting the electricity production.

Effective biodegradation of chlorophenols, sulfonamides, and their mixtures by bacterial laccase immobilized on chitin

Coexisting multi-pollutants like sulfonamides (SAs) and chlorophenols (CPs) in the ecological environment pose a potential risk to living organisms. The development of a strategy for the effective removal of multiple pollutants has become an urgent need. Herein, we systematically investigated the potential of immobilized bacterial laccase to remove chlorophenols (CPs), sulfonamides (SAs), and their mixtures. Laccase from Bacillus pumilus ZB1 was efficiently immobilized on chitin and its thermal stability, pH stability, and affinity to substrates were improved. Reusability assessment showed the immobilized laccase retained 75.5% of its initial activity after five cycles. The removal efficiency of CPs and SAs by immobilized laccase was significantly improved compared with that of free laccase. In particular, the removal of 2,4-dichlorophenol and 2,4,6-trichlorophenol reached 96.9% and 89.3% respectively within 8 h. The immobilized laccase could remove 63.70% of 2,4-dichlorophenol after four cycles. The degradation pathways of 2,4-dichlorophenol and sulfamethazine were proposed via LC/MS analysis. When the co-pollutants containing 2,4,6-trichlorophenol and sulfamethoxazole, immobilized laccase showed 100% removal of 2,4,6-trichlorophenol and 38.71% removal of sulfamethoxazole simultaneously. Cytotoxicity and phytotoxicity tests indicated that immobilized laccase can alleviate the toxicity of co-pollutants. The results demonstrate that chitin-based laccase immobilization can be an effective strategy for the removal of SAs, CPs, and their co-pollutants.

Textile azo dyes discolouration using spent mushroom substrate: enzymatic degradation and adsorption mechanisms

This study evaluated the adsorption and enzymatic degradation of azo dyes when using SMS. The laccase present in the SMS was characterised, and the maximum activity was obtained at pH 2, a temperature of 45°C, a Michaelis-Menten constant (Km) of 0.264 mM, and a maximum reaction rate (Vmax) of 117.95 µmol L-1 min-1. The presence of NaCl at 5 mM inhibited enzyme activity while no inhibition was observed by Na2SO4, typically found in textile wastewater. The maximum dye adsorption (57.22%) was achieved at pH 8.0, 25°C, and 100 g L-1 of SMS while the maximum enzymatic degradation (14.18%) was obtained under the same conditions, except at pH 4.0. The enzymes laccase, lignin peroxidase, and manganese peroxidase trapped in the SMS resulted in higher dye discolouration when compared to that extracted with aqueous solution, meaning that SMS has strong adsorption capacity and is a natural immobilisation matrix, which improves the enzymatic degradation of the dyes. Thus, SMS can be used in the treatment of textile effluents for dye removal by simultaneous mechanisms of adsorption and enzymatic degradation, with reduction of environmental impacts for SMS disposal and reduction of the costs associated with commercial enzymes and adsorbents.

Coupling of Fenton reaction and white rot fungi for the degradation of organic pollutants

Advanced oxidation processes (AOPs) are a class of highly efficient pollution remediation technologies that produce oxidising radicals under specific conditions to degrade organic pollutants. The Fenton reaction is a commonly applied AOP. To combine the advantages of AOPs and biodegradation in the remediation of organic pollutants, some studies have developed coupled systems between Fenton AOPs and white rot fungi (WRF) for environmental organic pollutant remediation and have achieved some success. Moreover, a promising system, termed as advanced bio-oxidation processes (ABOPs), mediated by the quinone redox cycling of WRF, has attracted increasing attention in the field. In this ABOP system, the radicals and H₂O₂ produced through the quinone redox cycling of WRF can strengthen Fenton reaction. Meanwhile, in this process, the reduction of Fe³⁺ to Fe²⁺ ensures the maintenance of Fenton reaction, leading to a promising application potential for the remediation of environmental organic pollutants. ABOPs combine the advantages of bioremediation and advanced oxidation remediation. Further understanding the coupling of Fenton reaction and WRF in the degradation of organic pollutants will be of great significance for the remediation of organic pollutants. Therefore, in this study, we reviewed recent remediation techniques for organic pollutants involving the coupled application of WRF and the Fenton reaction, focusing on the application of new ABOPs mediated by WRF, and discussed the reaction mechanism and conditions of ABOPs. Finally, we discussed the application prospects and future research directions of the joint application of WRF and advanced oxidation technologies for the remediation of environmental organic pollutants.

Progressive Biocatalysts for the Treatment of Aqueous Systems Containing Pharmaceutical Pollutants

The review focuses on the appearance of various pharmaceutical pollutants in various water sources, which dictates the need to use various methods for effective purification and biodegradation of the compounds. The use of various biological catalysts (enzymes and cells) is discussed as one of the progressive approaches to solving problems in this area. Antibiotics, hormones, pharmaceuticals containing halogen, nonsteroidal anti-inflammatory drugs, analgesics and antiepileptic drugs are among the substrates for the biocatalysts in water purification processes that can be carried out. The use of enzymes in soluble and immobilized forms as effective biocatalysts for the biodegradation of various pharmaceutical compounds (PCPs) has been analyzed. Various living cells (bacteria, fungi, microalgae) taken as separate cultures or components of natural or artificial consortia can be involved in biocatalytic processes under aerobic or anaerobic conditions. Cells as biocatalysts introduced into water treatment systems in suspended or immobilized form are used for deep biodegradation of PCPs. The potential of combinations of biocatalysts with physical-chemical methods of wastewater treatment is evaluated in relation to the effective removing of PCPs. The review analyzes recent results and the main current trends in the development of biocatalytic approaches to biodegradation of PCPs, the pros and cons of the processes and the biocatalysts used.

Simultaneous removal of tetracycline and sulfamethoxazole by laccase-mediated oxidation and ferrate(VI) oxidation: the impact of mediators and metal ions

This study explores the impact of mediators and metal ions of laccase-mediated oxidation and ferrate(VI) oxidation for the simultaneous removal of tetracycline antibiotics (TCs) and sulfonamide antibiotics (SAs) and to effectively remove their antimicrobial activity. The results showed that the antimicrobial activity of tetracycline against Bacillus altitudinis and Escherichia coli was significantly reduced, and the antimicrobial activity of sulfamethoxazole against B. altitudinis disappeared completely after treatment with the laccase-ABTS system. The combination of 6.0 U/mL of laccase and 0.2 mmol/L of ABTS removed 100% of 20.0 mg/L of tetracycline after 1.0 min at pH 6.0 and 25.0 °C, whereas the removal ratio of 20.0 mg/L of sulfamethoxazole was only 6.7%. The Al3+ and Cu2+ ions promoted the oxidation, and the Mn2+ ion decelerated the oxidation of tetracycline and sulfamethoxazole by the laccase-mediator systems. In contrast, the antimicrobial activity of tetracycline against B. altitudinis and E. coli was shown to be significantly reduced, and the sulfamethoxazole still retained high antimicrobial activity against B. altitudinis after treatment with Fe(VI) oxidation. The removal ratio of 20.0 mg/L of tetracycline was 100% after 1.0 min of treatment with 982.0 mg/L of K2FeO4 at pH 6.0 and 25.0 °C, whereas the removal ratio of 20.0 mg/L of sulfamethoxazole was only 49.5%. The Al3+, Cu2+, and Mn2+ ions both decelerated the oxidation of tetracycline and sulfamethoxazole by Fe(VI) oxidation. In general, the combination of the laccase-ABTS system and Fe(VI) was proposed for the simultaneous treatment of TCs and SAs in wastewater and to effectively remove their antimicrobial activity.

Microbial lignin valorization through depolymerization to aromatics conversion

Lignin is the most abundant source of renewable aromatic biopolymers and its valorization presents significant value for biorefinery sustainability, which promotes the utilization of renewable resources. However, it is challenging to fully convert the structurally complex, heterogeneous, and recalcitrant lignin into high-value products. The in-depth research on the lignin degradation mechanism, microbial metabolic pathways, and rational design of new systems using synthetic biology have significantly accelerated the development of lignin valorization. This review summarizes the key enzymes involved in lignin depolymerization, the mechanisms of microbial lignin conversion, and the lignin valorization application with integrated systems and synthetic biology. Current challenges and future strategies to further study lignin biodegradation and the trends of lignin valorization are also discussed.

Artificial microbial consortium producing oxidases enhanced the biotransformation efficiencies of multi-antibiotics

Antibiotic mixtures in the environment result in the development of bacterial strains with resistance against multiple antibiotics. Oxidases are versatile that can bio-remove antibiotics. Various laccases (LACs), manganese peroxidases (MNPs), and versatile peroxidase (VP) were reconstructed in Pichia pastoris. For the single antibiotics, over 95.0% sulfamethoxazole within 48 h, tetracycline, oxytetracycline, and norfloxacin within 96 h were bio-removed by recombinant VP with α-signal peptide, respectively. In a mixture of the four antibiotics, 80.2% tetracycline and 95.6% oxytetracycline were bio-removed by recombinant MNP2 with native signal peptide (NSP) within 8 h, whereas < 80.0% sulfamethoxazole was bio-removed within 72 h, indicating that signal peptides significantly impacted removal efficiencies of antibiotic mixtures. Regarding mediators for LACs, 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) resulted in better removal efficiencies of multi-antibiotic mixtures than 1-hydroxybenzotriazole or syringaldehyde. Furthermore, artificial microbial consortia (AMC) producing LAC2 and MNP2 with NSP significantly improved bio-removal efficiency of sulfamethoxazole (95.5%) in four-antibiotic mixtures within 48 h. Tetracycline and oxytetracycline were completely bio-removed by AMC within 48 and 72 h, respectively, indicating that AMC accelerated sulfamethoxazole, tetracycline, and oxytetracycline bio-removals. Additionally, transformation pathways of each antibiotic by recombinant oxidases were proposed. Taken together, this work provides a new strategy to simultaneously remove antibiotic mixtures by AMC.

Degradation of sulfonamides in aquaculture wastewater by laccase-syringaldehyde mediator system: Response surface optimization, degradation kinetics, and degradation pathway

As a new type of environmental pollutant, environmental antibiotic residues have attracted widespread attention, and the degradation and removal of antibiotics has become an engaging topic for scholars. In this paper, Novozym 51003 industrialized laccase and syringaldehyde were combined to degrade sulfonamides in aquaculture wastewater. Design Expert10 software was used for multiple regression analysis, and a response surface regression model was established to obtain the optimal degradation parameters. In the actual application, the degradation system could maintain a stable performance within 9 h, and timely supplement of the mediator could achieve a better continuous degradation effect. Low concentrations of heavy metals and organic matter would not significantly affect the degradation performance of the laccase-mediator system, making the degradation system suitable for a wide range of water quality. Enzymatic reaction kinetics demonstrated a strong affinity of sulfadiazine to the substrate. Ten degradation products were speculated using high-resolution mass spectrum based on the mass/charge ratios and the publication results. Four types of possible degradation pathways of sulfadiazine were deduced. This work provides a practical method for the degradation and removal of sulfonamide antibiotics in actual sewage.

Biodegradation of sulfonamide antibiotics through the heterologous expression of laccases from bacteria and investigation of their potential degradation pathways

In this study, seven laccase genes from different bacteria were linked with the signal peptides PelB, Lpp or Ompa for heterologous expression in E. coli. The recombinant strains were applied for the removal of sulfadiazine (SDZ), sulfamethazine (SMZ), and sulfamethoxazole (SMX). The results obtained for different signal peptides did not provide insights into the removal mechanism. The removal ratios of SDZ, SMZ, and SMX obtained with the recombinant strain 6#P at 60 h were around 92.0%, 89.0%, and 88.0%, respectively. The degradation pathways of sulfonamides have been proposed, including SO₂ elimination, hydroxylation, oxidation, pyrimidine ring cleavage, and N-S bond cleavage. Different mediators participate in the degradation of antibiotics through different mechanisms, and different antibiotics have different responses to the same mediator. The addition of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) slightly promoted the removal of sulfonamides by most recombinant strains with different signal peptides, especially for the recombinant strain 2#O. The removal of sulfonamides by 1-hydroxybenzotriazole (HBT) varied with the recombinant strains. Syringaldehyde (SA) had a slight inhibitory effect on the removal of sulfonamides, with the most significant effect on strains 7#L and 7#O.

Introducing a Thermo-Alkali-Stable, Metallic Ion-Tolerant Laccase Purified From White Rot Fungus Trametes hirsuta

This study introduces a valuable laccase, designated ThLacc-S, purified from white rot fungus Trametes hirsuta. ThLacc-S is a monomeric protein in nature with a molecular weight of 57.0 kDa and can efficiently metabolize endocrine disrupting chemicals. The enzyme was successfully purified to homogeneity via three consecutive steps consisting of salt precipitation and column chromatography, resulting in a 20.76-fold increase in purity and 46.79% yield, with specific activity of 22.111 U/mg protein. ThLacc-S was deciphered as a novel member of the laccase family and is a rare metalloenzyme that contains cysteine, serine, histidine, and tyrosine residues in its catalytic site, and follows Michaelis-Menten kinetic behavior with a K _m and a k _cat /K _m of 87.466 μM and 1.479 s^-1μM^-1, respectively. ThLacc-S exerted excellent thermo-alkali stability, since it was markedly active after a 2-h incubation at temperatures ranging from 20 to 70°C and retained more than 50% of its activity after incubation for 72 h in a broad pH range of 5.0-10.0. Enzymatic activities of ThLacc-S were enhanced and preserved when exposed to metallic ions, surfactants, and organic solvents, rendering this novel enzyme of interest as a green catalyst for versatile biotechnological and industrial applications that require these singularities of laccases, particularly biodegradation and bioremediation of environmental pollutants.

Anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) for treatment of high concentration p-nitrophenol wastewater under shock loading conditions

P-nitrophenol (PNP or 4-NP) has been widely used as a biorefractory raw material in chemical industry, whereas been highly concerned for its characteristics of mutagenic/carcinogenic activity and food chain bioaccumulation. In this study, an anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) was constructed and used to treat PNP wastewater which discharged from chemical industries. Experimental results revealed that the An-SFB-BR was successfully cultivated with the gradually increasing of influent PNP from 0 to 540 mg/L (gradually increased 10 mg/L every time in stage II and 30-50 mg/L for stage III), with the observation of an average removal efficiency of 98% for PNP and 80% for chemical oxygen demand (COD), also a biogas production and biogas production rate of 2.1 L/(L·d) and 0.57 m³/kg-COD, respectively. Finally, the conversion rate of P-aminophenol (PAP), the primary intermediate of PNP reached 80% after An-SFB-BR biodegradation. A relatively stable pH was maintained throughout the entire process, and insignificant VFA accumulation. The reactor exhibited a strong toxic shock resistance, and 16S rRNA sequencing results demonstrated that the dominant microbial community changed slightly with the gradually increasing of PNP concentration, which guaranteed the PNP removal efficiency.

Feed-additive of bioengineering strain with surface-displayed laccase degrades sulfadiazine in broiler manure and maintains intestinal flora structure

Sulfonamide antibiotics (SAs) are excreted into the ecosystem unchanged through feces and urine because of their low adsorption and degradation in the guts of humans and animals. In this study, a novel whole-cell biocatalyst with fungal laccase on the cell surface of Escherichia coli Nissle 1917 was developed to degrade sulfadiazine (SDZ). Engineered strain EcN-IL showed laccase enzyme activity of 2 ± 1 U/mg dry weight of cell and degraded 37 ± 1% of SDZ at temperature 40 °C and pH 5 within 3 h in vitro. Strain EcN-IL with 500 mg/kg of SDZ was employed as a food supplement to feed chicken broilers, which can reduce the residue of SDZ in broiler manure by 58 ± 2% and also reduced dysbiosis of the gut microbiota due to overuse of antibiotics. The genetically engineered EcN-IL has laid a foundation for degrading SDZ in broilers and their manure.

Substrate specificity of a new laccase from Trametes polyzona WRF03

Various aromatic compounds that are structurally analogous to lignin were tested as possible/preferred substrates for purified laccase from newly isolated white rote fungi, Trametes polyzona WRF03. The pH optima were tested using different substrates and kinetic studies were conducted at these pH optima. The pH optima in the presence of ABTS, α-naphthol, o-dianisidine, and catechol were 4.5 but 5.0 and 5.5 in the presence of guaiacol and pyrogallol, respectively. The initial velocities obtained from the kinetic study were analyzed using Graph Pad Prism 7 and Lineweaver-Burk plot to obtain kinetic constants (k_m and _Vmax) which were used to calculate substrate specificity. Amongst all the substrates tested, ABTS had the highest specificity-constant (181.51 M⁻¹s⁻¹), and therefore, the most preferred substrate was followed by α-naphthol, o-dianisidine, guaiacol, pyrogallol, and catechol. Resorcinol, orcinol, and veratryl alcohol did not display any considerable chemical shift in the presence of Trametes polyzona WRF03 laccase. Also, oxidation of phenolic substrates appeared to be dependent on the nature of the substituent groups and their relative position on the aromatic nucleus. Since most of these substrates are structural analogs of lignin and many recalcitrant environmental pollutants, the enzyme may find application in delignification, treatment of wastewater containing dyes, and polycyclic aromatic hydrocarbons (PAHs).

Exploring the effects of volcanic eruption disturbances on the soil microbial communities in the montane meadow steppe

Volcanic eruptions are important components of natural disturbances that provide a model to explore the effects of volcanic eruption disturbances on soil microorganisms. Despite widespread research, to the best of our knowledge, no studies of volcanic eruption disturbances have investigated the effects on soil microbial communities in the montane meadow steppe. To address this gap, we meticulously investigated the characteristics of the soil microbial communities from the volcano and steppe sites using Illumina MiSeq high-throughput sequencing. Hierarchical clustering analysis and principal coordinate analysis (PCoA) showed that the soil microbial communities from the volcano and steppe sites differed. The diversity and richness of the soil microbial communities from the steppe sites were significantly higher than at the volcano sites (P < 0.05), and the soil microbial communities in the steppe sites had higher stability. The effects of volcanic eruption disturbances on the bacterial community development are greater than its effects on the fungal communities. The environmental filtering of volcanic eruptions selectively retained some special microorganisms (i.e., Conexibacter, Agaricales, and Gaiellales) with strong adaptability to the environmental disturbances, enhanced metabolic activity for sodium and calcium reabsorption, and increased relative abundances of the lichenized saprotrophs. The soil microbial communities from the volcano and steppe sites cooperate to form complex networks of species interactions, which are strongly influenced by the interaction of the soil and vegetation factors. Our findings provide new information on the effects of volcanic eruption disturbances on the soil microbial communities in the montane meadow steppe.

Pichia pastoris — recombinant enzyme producent for environment treatment — review

Since environmental pollution is increasing, scientists try to find a sustainable way for its clean up and for environment protection. Due to increasing knowledge of genetics and recombinant technologies, recombinant enzymes have been increasingly applied for these purposes. This article deals with the possibilities of environmental treatment with different types of enzymes produced by P. pastoris. Environment is polluted mostly with pesticides, wastewaters, phenol compounds, plastics, toxic compounds, wastes from medical treatment, etc. All these compounds have to be eliminated considering the deteriorating biodiversity, human health, and condition of plants. Enzymes are an environmentally friendly way of such treatment.

Oxidative enzymes from newly local strain Aspergillus iizukae EAN605 using pumpkin peels as a production substrate: Optimized production, characterization, application and techno-economic analysis

The present study deals with optimizing, producing, characterizing, application and techno- economic analysis of oxidative enzymes [Laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP)] from Aspergillus iizukae EAN605 in submerged fermentation process using pumpkin peels as a production substrate. The best operating parameters for producing Lac, MnP and LiP (6.15, 2.58 and 127.99 U mg^-1 respectively) were recorded with 20 g 100 mL^-1 of substrate, 4.6 mL 100 mL^-1 of inoculum size at pH 5.5 after 10 days. The crude enzyme exhibited high stability at pH (3-9) and temperatures (20-60 °C). K_m (Michaelis-Menten) of Lac, MnP and LiP crude enzyme was 2.25, 1.79 and 0.72 mM respectively. The decolourization of Remazol Brilliant Blue R by the crude enzyme was 84.84 %. The techno-economic analysis was assessed for a production unit with an annual operating time for enzymatic production and application is 7920 h/year and 100 m³ of the capacity. The process would produce 27,000 cm³ of crude enzyme with a price of USD 0.107 per cm³ compared to USD 1 per cm³ of the current commercial enzyme. The findings indicated that pumpkin peels have potential as a production substrate for oxidative enzymes from A. iizukae EAN605 and is economically feasible.

Biodegradation and toxicity reduction of nonylphenol, 4-tert-octylphenol and 2,4-dichlorophenol by the ascomycetous fungus Thielavia sp HJ22: Identification of fungal metabolites and proposal of a putative pathway

Research on the biodegradation of emerging pollutants is gained great focus regarding their detrimental effects on the environment and humans. The objective of the present study was to evaluate the ability of the ascomycetes Thielavia sp HJ22 to remove the phenolic xenobiotics nonylphenol (NP), 4-tert-octylphenol (4-tert-OP) and 2,4-dichlorophenol (2,4-DCP). The strain showed efficient degradation of NP and 4-tert-OP with 95% and 100% removal within 8 h of incubation, respectively. A removal rate of 80% was observed with 2,4-DCP within the same time. Under experimental conditions, the degradation of the tested pollutants concomitantly increased with the laccase production and cytochrome P450 monooxygenases inhibition. This study showed the involvement of laccase in pollutants removal together with biosorption mechanisms. Additionally, results demonstrated the participation of cytochrome P450 monooxygenase in the elimination of 2,4-DCP. Liquid chromatography-mass spectrometry analysis revealed several intermediates, mainly hydroxylated and oxidized compounds with less harmful effects compared to the parent compounds. A decrease in the toxicity of the identified metabolites was observed using Aliivibrio fischeri as bioindicator. The metabolic pathways of degradation were proposed based on the identified metabolites. The results point out the potential of Thielavia strains in the degradation and detoxification of phenolic xenobiotics.

Pichia pastoris: A highly successful expression system for optimal synthesis of heterologous proteins

One of the most important branches of genetic engineering is the expression of recombinant proteins using biological expression systems. Nowadays, different expression systems are used for the production of recombinant proteins including bacteria, yeasts, molds, mammals, plants, and insects. Yeast expression systems such as Saccharomyces cerevisiae (S. cerevisiae) and Pichia pastoris (P. pastoris) are more popular. P. pastoris expression system is one of the most popular and standard tools for the production of recombinant protein in molecular biology. Overall, the benefits of protein production by P. pastoris system include appropriate folding (in the endoplasmic reticulum) and secretion (by Kex2 as signal peptidase) of recombinant proteins to the external environment of the cell. Moreover, in the P. pastoris expression system due to its limited production of endogenous secretory proteins, the purification of recombinant protein is easy. It is also considered a unique host for the expression of subunit vaccines which could significantly affect the growing market of medical biotechnology. Although P. pastoris expression systems are impressive and easy to use with well‐defined process protocols, some degree of process optimization is required to achieve maximum production of the target proteins. Methanol and sorbitol concentration, Mut forms, temperature and incubation time have to be adjusted to obtain optimal conditions, which might vary among different strains and externally expressed protein. Eventually, optimal conditions for the production of a recombinant protein in P. pastoris expression system differ according to the target protein.

The roles of Pleurotus ostreatus HAUCC 162 laccase isoenzymes in decolorization of synthetic dyes and the transformation pathways

Fungal laccases have shown great potential in industrial and environmental applications. They are generally produced as laccase isoenzymes. Thus, to further study the properties of different laccase isoenzymes and their performance in bio-remediation is essential for a deep understanding of laccase function and application. In this study, three Pleurotus ostreatus HAUCC 162 laccase isoenzymes were heterologously expressed, and the effects of different inhibitors, metal ions, and organic solvents on the activity of recombinant laccases were evaluated. In the dye decolorization test, LACC6 showed the highest ability to remove Malachite green (MG), Remazol Brilliant Blue R (RBBR), Bromophenol blue (BB), and Methyl orange (MO) among the three recombinant laccases. Removal rates within 24 h were 91.5%, 84.9%, 79.1%, and 73.1% for MG (100 mg/L), RBBR (100 mg/L), BB (100 mg/L), and MO (100 mg/L), respectively. The MG and RBBR transformation pathways were proposed by using High Performance Liquid Chromatography-Mass Spectrometry (LC-MS) analysis. Based on the results of this work, the production of recombinant LACC6 or improving the portion of LACC6 in the crude extracellular laccase may advance synthetic dye removal.

Cohnella sp. A01 laccase: thermostable, detergent resistant, anti-environmental and industrial pollutants enzyme

Laccase (EC 1.10.3.2; benzenediol; oxygen oxidoreductases) is a multi-copper oxidase that catalyzes the oxidation of phenols, polyphenols, aromatic amines, and different non-phenolic substrates with concomitant reduction of O₂ to H₂O. Enzymatic oxidation techniques have the potential of implementation in different areas of industrial fields. In this study, the Cohnella sp. A01 laccase gene was cloned into pET-26 (b+) vector and was transformed to E. coli BL21. Then it was purified using His tag affinity (Ni sepharose resin) chromatography. The estimated molecular weight was approximately 60 kDa using SDS-PAGE. The highest enzyme activity and best pH for 2,6-dimethoxyphenol (DMP) oxidation were recorded as 8 at 90 °C respectively. The calculated half-life and kinetic values including K_m, V_max, turn over number (k_cat), and catalytic efficiency (k_cat/K_m) of the enzyme were 106 min at 90 °C and 686 μM, 10.69 U/ml, 20.3 S⁻, and 0.029 s⁻¹ μM⁻¹, respectively. The DMP was available as the substrate in all the calculations. Enzyme activity enhanced in the presence of Cu²⁺, NaCl, SDS, n-hexane, Triton X-100, tween 20, and tween 80, significantly. The binding residues were predicted and mapped upon the modeled tertiary structure of identified laccase. The remaining activity and structural properties of Cohnella sp. A01 laccase in extreme conditions such as high temperatures and presence of metals, detergents, and organic solvents suggest the potential of this enzyme in biotechnological and industrial applications. This process has been patented in Iranian Intellectual Property Centre under License No: 91325.

Metal and metal-oxide nanozymes: bioenzymatic characteristics, catalytic mechanism, and eco-environmental applications

Phenolic contaminants (R-OH) are a category of highly toxic organic compounds that are widespread in aquatic ecosystems and can induce carcinogenic risk to wildlife and humans; natural enzymes as green catalysts are capable of step-polymerizing these compounds to produce diverse macromolecular self-coupling products via radical-mediated C-C and C-O-C bonding at either the ortho- or para-carbon position, thereby evading the bioavailability and ecotoxicity of these compounds. Intriguingly, certain artificial metal and metal-oxide nanomaterials are known as nanozymes. They not only possess the unique properties of nanomaterials but also display intrinsic enzyme-mimicking activities. These artificial nanozymes are expected to surmount the shortcomings, such as low stability, easy inactivation, difficult recycling, and high cost, of natural enzymes, thus contributing to eco-environmental restoration. This review highlights the available studies on the enzymatic characteristics and catalytic mechanisms of natural enzymes and artificial metal and metal-oxide nanozymes in the removal and transformation of R-OH. These advances will provide key research directions beneficial to the multifunctional applications of artificial nanozymes in aquatic ecosystems.

An ionic liquid functionalized polymer for simultaneous removal of four phenolic pollutants in real environmental samples

An ionic liquid functionalized polymer (IL-P) was prepared feasibly and simply by grafting1-butyl-3-vinylimidazolium bromide onto the silica surface. The IL-P was fully characterized, and the results showed that IL-P has a rough surface with a lower specific surface area (205.49 m² g^-1), and the involvement of ionic liquid significantly improved the adsorption performance of IL-P. The pH, initial concentration, adsorption time and temperature were investigated to discuss the adsorption behaviors of IL-P in aqueous solution. The adsorption process of 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA) and 2,4-dinitrophenol (2,4-DNP) onto IL-P better fitted the pseudo-second-order model, while that of 2-isonaphthol (2-NP) followed the pseudo-first-order model. The adsorption behaviors of IL-P towards 2,4-DCP and 2,4-DNP fitted well with Liu isotherm model, and that of BPA and 2-NP can be described by Langmuir model. The maximum adsorption capacities of 2,4-DCP, BPA, 2,4-DNP and 2-NP bound on IL-P was 239.7, 68.39, 56.86 and 64.28 mg g^-1, respectively, and the adsorption of IL-P is a spontaneous physical process. Comparing with other adsorbent, the as-prepared IL-P showed excellent recognition ability towards the phenolic compounds and can be applied to adsorb and remove trace 2,4-DCP, 2-NP, 2,4-DNP and BPA simultaneously in complicated wastewater and soil samples.

Improvements of thermophilic enzymes: From genetic modifications to applications

Thermozymes (from thermophiles or hyperthermophiles) offer obvious advantages due to their excellent thermostability, broad pH adaptation, and hydrolysis ability, resulting in diverse industrial applications including food, paper, and textile processing, biofuel production. However, natural thermozymes with low yield and poor adaptability severely hinder their large-scale applications. Extensive studies demonstrated that using genetic modifications such as directed evolution, semi-rational design, and rational design, expression regulations and chemical modifications effectively improved enzyme's yield, thermostability and catalytic efficiency. However, mechanism-based techniques for thermozymes improvements and applications need more attention. In this review, stabilizing mechanisms of thermozymes are summarized for thermozymes improvements, and these improved thermozymes eventually have large-scale industrial applications.

Heterologous expression and characterization of a xylanase and xylosidase from white rot fungi and their application in synergistic hydrolysis of lignocellulose

Endo-xylanase and β-xylosidase are the major enzymes for hemicellulose hydrolysis, which play a significant role in biomass conversion. In our previous work, the white-rot fungi Pleurotus ostreatus HAUCC 162 and Irpex lacteus CD2 were demonstrated to have strong ability in lignocellulose degradation, and the related lignin degradation enzymes were characterized. However, little was known about their hemicellulases. In this work, a novel endo-1, 4-xylanase and a β-xylosidase from Pleurotus ostreatus HAUCC 162 and Irpex lacteus CD2 were heterologously expressed and characterized. The optima of pH and temperature were 5.0 and 55 °C for rXyn162, and 6.5 and 30 °C for rXylCD2. rXyn162 showed high tolerance to metal ions such as Ca²⁺, Cr³⁺, Zn²⁺, Na⁺, and Al³⁺. The recombinant rXyn162 and rXylCD2 exhibited synergistic hydrolysis of oat spelts xylan and sodium hydroxide pretreated cornstalk (SHPC), where the degree of synergy (DS) was 2.26 for SHPC hydrolysis. MALDI-TOF-MS and HPLC analysis showed that xylooligosaccharides (XOS) with small degrees of polymerization (DP2-DP4) were the major XOS hydrolyzate during SHPC degradation by rXyn162 and rXylCD2. In addition, rXyn162 and rXylCD2 could efficiently improve the hydrolysis of SHPC by commercial cellulase. The present study suggested the potential application of rXyn162 and rXylCD2 in the field of biomass pretreatment and biofuel production.

Bifunctional in vivo role of laccase exploited in multiple biotechnological applications

Laccases are multicopper enzymes present in plants, fungi, bacteria, and insects, which catalyze oxidation reactions together with four electron reduction of oxygen to water. Plant, bacterial, and insect laccases have a polymerizing role in nature, implicated in biosynthesis of lignin, melanin formation, and cuticle hardening, respectively. On the other hand, fungal laccases carry out both polymerizing (melanin synthesis and fruit body formation) as well as depolymerizing roles (lignin degradation). This bifunctionality of fungal laccases can be attributed to the presence of multiple isoforms within the same as well as different genus and species. Interestingly, by manipulating culture conditions, these isoforms with their different induction patterns and unique biochemical characteristics can be expressed or over-expressed for a targeted biotechnological application. Consequently, laccases can be considered as one of the most important biocatalyst which can be exploited for divergent industrial applications viz. paper pulp bleaching, fiber modification, dye decolorization, bioremediation as well as organic synthesis. The present review spotlights the role of fungal laccases in various antagonistic applications, i.e., polymerizing and depolymerizing, and co-relating this dual role with potential industrial significance.

Purification and characterization of a fungal laccase from the ascomycete Thielavia sp. and its role in the decolorization of a recalcitrant dye

A laccase-producing ascomycete was isolated from arid soil in Tunisia. This fungus was identified as Thielavia sp. using the phylogenetic analysis of rDNA internal transcribed spacers. The extracellular laccase produced by the fungus was purified to electrophoretic homogeneity, showing a molecular mass around 70 kDa. The enzyme had an optimum pH of 5.0 and 6.0 for ABTS and 2,6‑DMP, respectively and it showed remarkable high thermal stability, showing its optimal temperature at 70 °C (against 2,6‑DMP). It presented slight inhibiting effect by EDTA, SDS and l‑cyst although this effect was more marked by sodium azide (0.1 mM). On the other hand, it showed tolerance to up to 300 mM NaCl, retaining around 50% of its activity at 900 mM. Among the metal ions tested on TaLac1, Mn²⁺ showed an activating effect. Their kinetic parameters K_m and k_cat were 23.7 μM and 4.14 s^-1 for ABTS, and 24.3 μM and 3.46 s^-1 towards 2,6‑DMP. The purified enzyme displayed greater efficiency in Remazol Brilliant Blue R decolorization (90%) in absence of redox mediator, an important property for biotechnological applications.