Extracellular expression of mutant CotA-laccase SF in Escherichia coli and its degradation of malachite green

Isolation, identification, and characterisation of the malachite green detoxifying bacterial strain Bacillus pacificus ROC1 and the azoreductase AzrC

Malachite green (MG) is used as a dye for materials such as wood, cotton, and nylon, and is used in aquaculture to prevent fungal and protozoan diseases. However, it is highly toxic, with carcinogenic, mutagenic, and teratogenic properties, resulting in bans worldwide. Despite this, MG is still frequently used in many countries due to its efficacy and economy. MG is persistent in the environment and so requires degradative intervention. In this work we isolated Bacillus pacificus ROC1 strain from a salt flat in Pakistan that had the ability to aerobically detoxify MG, as determined by bacterio- and phyto-toxicity assays. We demonstrate immobilized B. pacificus ROC1 can effectively detoxify MG, which highlights a potential method for its biodegradation. Genomic sequencing identified three candidate azo-reductases within B. pacificus ROC1 that could be responsible for the MG-degrading activity. These were cloned, expressed and purified from Escherichia coli, with one (AzrC), catalyzing the reduction of MG to leuco-MG in vitro. AzrC was crystallised and MG was captured within the active site in a Michaelis complex, providing structural insight into the reduction mechanism. Altogether, this work identifies a bacterium capable of aerobically degrading a major industrial pollutant and characterizes the molecular basis for this activity.

Anisotropic Chitosan-nanocellulose/Zeolite imidazolate frameworks-8 aerogel for sustainable dye removal

Assembling microscopic metal-organic frameworks into macroscopic polymeric scaffolds to develop highly renewable materials has been a promising yet challenging area of research. Herein, chitosan (CS) blended with nano-cellulose (NC) was unidirectionally transformed into an aerogel with oriented macropores and then biomineralized with zeolite imidazolate frameworks-8 (ZIF-8) to form a hierarchical structured chitosan-nanocellulose/zeolite imidazolate frameworks-8 (CS-NC-ZIF-8) hybrid aerogel. Incorporating ZIF-8 significantly increases the versatility and mechanical strength with a Young's modulus of 14.18 MPa of the CS-NC aerogel. The incorporation of ZIF-8 into the aerogel not only enhances its adsorption capacity for methylene blue, rhodamine B, acid fuchsin, and methyl orange, but also facilitates the generation of electrons from water that can be transferred to degrade > 90 % of malachite green within 90 min in each catalytic cycle, and this capability was maintained for at least 10 consecutive cycles. Remarkably, the hybrid aerogel was highly renewable after the adsorption of cationic dyes and catalytic removal of malachite green. With its facile production process, high removal efficiency, affordable and green nature, and excellent regeneration feasibility, the CS-NC-ZIF-8 aerogel stands as a promising solution for addressing challenges associated with dye-contaminated water treatment.

Bioremediation of azo dye: A review on strategies, toxicity assessment, mechanisms, bottlenecks and prospects

The synthetic azo dyes are widely used in the textile industries for their excellent dyeing properties. They may be classified into many classes based on their structure and application, including direct, reactive, dispersive, acidic, basic, and others. The continuous discharge of wastewater from a large number of textile industries without prior treatment poses detrimental effects on the environment and human health. Azo dyes and their degradation products are extremely poisonous for their carcinogenic, teratogenic and mutagenic nature. Moreover, exposure to synthetic azo dyes can cause genetic changes, skin inflammation, hypersensitivity responses, and skin irritations in persons, which may ultimately result in other profound issues including the deterioration of water quality. This review discusses these dyes in details along with their detrimental effects on aquatic and terrestrial flora and fauna including human beings. Azo dyes degrade the water bodies by increasing biochemical and chemical oxygen demand. Therefore, dye-containing wastewater should be effectively treated using eco-friendly and cost-effective technologies to avoid negative impact on the environment. This article extensively reviews on physical, chemical and biological treatment with their benefits and challenges. Biological-based treatment with higher hydraulic retention time (HRT) is economical, consumes less energy, produces less sludge and environmentally friendly. Whereas the physical and chemical methods with less hydraulic retention time is costly, produces large sludge, requires high dissolved oxygen and ecologically inefficient. Since, biological treatment is more advantageous over physical and chemical methods, researchers are concentrating on bioremediation for eliminating harmful azo dye pollutants from nature. This article provides a thorough analysis of the state-of-the-art biological treatment technologies with their developments and effectiveness in the removal of azo dyes. The mechanism by which genes encoding azoreductase enzymes (azoG, and azoK) enable the natural degradation of azo dyes by bacteria and convert them into less harmful compounds is also extensively examined. Therefore, this review also focuses on the use of genetically modified microorganisms and nano-technological approaches for bioremediation of azo dyes.

Strategy for Highly Efficient Detection and Removal of Raman Inactive Leuco-Malachite Green on Environmentally Friendly Graphitic Carbon Nitride-Based Nanostructures

The sustainable identification and efficient degradation of some recessive and seriously toxic pollutants are important issues in practical applications. Herein, a portable platform (EAl/ACN/Ag) constructed by growing AgNPs in situ in the cavities of the alkalized carbon nitride (ACN) coated on the etched Al sheet (EAl) is achieved. Interestingly, on the constructed EAl/ACN/Ag substrate irradiated by light for 3 min, a Raman inactive leuco-malachite green (LMG: a highly toxic and environmentally persistent pollutant that is difficult to be found due to being colorless) can be sensitively and selectively detected by surface-enhanced Raman scattering spectroscopy (SERS). Results demonstrate that the abundant •O2-, •OH, and h+ active species produced by irradiation of the EAl/ACN/Ag are responsible for the sensitive and selective SERS detection of the Raman-inactive LMG. The green and sustainable initiation in the sensitive SERS detection of LMG is greatly different from those by the traditional chemical process. The limit of detection of LMG can reach 8.99 × 10-13 mol·L-1, which is superior to some other methods for LMG detection in real samples. In addition, the EAl/ACN/Ag substrate displays excellent photocatalytic activity for LMG molecules. The research will provide a new and green way for the sensitive detection and efficient removal of some recessive and toxic pollutants in food fields and environmental analyses.

Combined Strategies for Improving Aflatoxin B1 Degradation Ability and Yield of a Bacillus licheniformis CotA-Laccase

Aflatoxin B1 (AFB1) contamination is a serious threat to nutritional safety and public health. The CotA-laccase from Bacillus licheniformis ANSB821 previously reported by our laboratory showed great potential to degrade AFB1 without redox mediators. However, the use of this CotA-laccase to remove AFB1 in animal feed is limited because of its low catalytic efficiency and low expression level. In order to make better use of this excellent enzyme to effectively degrade AFB1, twelve mutants of CotA-laccase were constructed by site-directed mutagenesis. Among these mutants, E186A and E186R showed the best degradation ability of AFB1, with degradation ratios of 82.2% and 91.8% within 12 h, which were 1.6- and 1.8-times higher than those of the wild-type CotA-laccase, respectively. The catalytic efficiencies (kcat/Km) of E186A and E186R were found to be 1.8- and 3.2-times higher, respectively, than those of the wild-type CotA-laccase. Then the expression vectors pPICZαA-N-E186A and pPICZαA-N-E186R with an optimized signal peptide were constructed and transformed into Pichia pastoris GS115. The optimized signal peptide improved the secretory expressions of E186A and E186R in P. pastoris GS115. Collectively, the current study provided ideal candidate CotA-laccase mutants for AFB1 detoxification in food and animal feed and a feasible protocol, which was desperately needed for the industrial production of CotA-laccases.

Decolorization and detoxication of malachite green by engineered Saccharomyces cerevisiae expressing novel thermostable laccase from Trametes trogii

Malachite Green (MG) is a widely used industrial dye that is hazardous to health. Herein, the decolourisation and detoxification of MG were achieved using the engineered Saccharomyces cerevisiae expressing novel thermostable laccase lcc1 from Trametes trogii. The engineered strain RCL produced a high laccase activity of 121.83 U L-1. Lcc1 was stable at temperatures ranging from 20 ℃ to 60 ℃ and showed a high tolerance to organic solvents. Moreover, Lcc1 could decolorize different kinds of dyes (azo, anthraquinone and triphenylmethane), among which, the decolorization ability of MG is the highest, reaching 95.10 %, and the decolorization rate of other triphenylmethane dyes also over 50 %. The RCL decolorized about 95 % of 50 mg L-1 of MG dye in 10 h at 30 ℃. The MG degradation products were analyzed. The industrial application potential of the RCL was evaluated by treating industrial wastewater and the decolourisation rates were over 90 %.

Engineering Site 228 of Streptomyces coelicolor Laccase for Optimizing Catalytic Activity

Malachite green (MG) poses a formidable threat to ecosystems and human health. Laccase emerges as a promising candidate for MG degradation, prompting an investigation into the catalytic activity modulation of a small laccase (SLAC) from Streptomyces coelicolor, with a focus on amino acid position 228. Through saturation mutagenesis, five mutants with a 50% increase in the specific activity were generated. Characterization revealed notable properties, Km of E228F was 8.8% of the wild type (WT), and E288T exhibited a 133% kcat compared to WT. Structural analyses indicated improved hydrophobicity and electrostatic potential on the mutants' surfaces, with the stable E228F-ABTS complex exhibiting reduced flexibility, possibly contributing to the observed decrease in turnover rate. Mutants demonstrated enhanced MG decolorization, particularly E228G. Site 228 acts as a crucial functional control switch, suggesting its potential role in SLAC engineering. This study provides insights into laccase modulation and offers promising avenues for enzymatic bioremediation applications.

Biodegradation of malachite green by Pleurotus eryngii: a study on decolorization, mechanism, toxicity, and enzyme

The purpose of this study was to investigate the biodegradation of malachite green (MG) by Pleurotus eryngii via decolorization. This study also explored the possible mechanisms and toxicity. The results indicated that this fungus exhibited strong decolorizing potential. MG degradation based on UPLC-TOF-Triple-MS analysis revealed the formation of intermediates such as 4-(dimethylamino)benzophenone, 4-(methylamino)benzophenone, and 4-(dimethylamino)phenol. Furthermore, a significant reduction in the toxicity of the degradation products was observed using the zebrafish animal model. A newly discovered dye-decolorizing peroxidase (DyP-PE) from P. eryngii was amplified, cloned, and expressed. The purified 56.4 kDa DyP-PE strongly decolorized MG, suggesting potentially application in the bioremediation of MG pollution. Thus, the DyP-PE derived from P. eryngii may contribute to the degradation of MG.

Production and characterization of novel thermostable CotA-laccase from Bacillus altitudinis SL7 and its application for lignin degradation

Laccases are multi-copper oxidases and found in ligninolytic bacteria catalyzing the oxidation of both phenolic and non-phenolic compounds, however its application in lignin degradation suffers due to low oxidation rate, which have intensified the search for new laccases. In the present study, spore coat A protein (CotA) encoding gene having laccase like activity from Bacillus altitudinis SL7 (CotA-SL7) was cloned and expressed in Escherichia coli. The purified CotA-SL7 was active at wide range of temperature and pH with optimum activity at 55 °C and pH 5.0. The kinetic parameters of CotA-SL7 was determined with Km, Vmax, and kcat values 0.4 mM, 2777 μmol/min/mg, and 5194 s-1, respectively. Molecular docking revealed the presence of Pro, Phe, Asp, Asn, His, and Ile residues at the active site taking part in the oxidation of ABTS. The purified CotA-SL7 reduced lignin contents by 31 % and changes in lignin structure were analyzed through fourier transformed infrared spectroscopy (FTIR), scanning electron microsscopy (SEM) and gas chromatography mass-spectrometry (GC-MS). The appearance of low molecular size compounds clearly indicates the cleavage of lignin polymer and opening of the benzene ring by purified CotA-SL7. Thus, high catalytic efficiency of CotA-SL7 makes it a suitable bio-catalyst for remediation of lignin contaminated wastewater from pulp and paper industries with clear insights into lignin degradation at molecular level.

Degradation of malachite green by g-C3N4-modified magnetic attapulgite composites under visible-light conditions

Water resources are seriously threatened by dye wastewater, and the removal of the dye molecules from the wastewater has garnered considerable interest. People have favored photocatalytic technology in recent years for the treatment of dye wastewater. In this work, attapulgite (ATP) was used as a carrier, Fe3O4 and g-C3N4 were grafted onto ATP, and the surface was then modified with polyethyleneimine (PEI) to produce photocatalyst ATP-Fe3O4-g-C3N4-PEI, which was used in Malachite green (MG) dye wastewater. The structure and surface properties of the composites were analyzed and characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray spectrum (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Uv-vis spectrum analysis, zeta potential measurement, and vibrating-sample magnetometry (VSM) analysis. The removal performance of ATP-Fe3O4-gC3N4-PEI for MG was studied, and the removal mechanism was explored and revealed. It has been shown that the heterojunction formed by Fe3O4 and g-C3N4 can inhibit the compounding of photogenerated electrons and holes, effectively improving the performance of the ATP-Fe3O4-g-C3N4-PEI. Electron paramagnetic resonance (EPR) analysis confirmed that ATP-Fe3O4-g-C3N4-PEI could generate hydroxyl radicals (·OH) and superoxide radicals (·O2-) to degrade the MG. It was believed that ATP-Fe3O4-g-C3N4-PEI could generate hydroxyl radicals (·OH) through the photocatalysis and the Fenton reaction of the composite materials. Under the action of H+, ·O2-, and ·OH, the removal rate of MG by ATP-Fe3O4-g-C3N4-PEI exceeded 98 % at an optimal condition. The intermediate products and degradation pathways of MG degradation were also inferred by LC-MS analysis. These results showed that the prepared photocatalyst has excellent degradation performance for MG and could be used in dye wastewater treatment.

Dye degradation by early colonizing marine bacteria from the Arabian Sea, India

Malachite green dye belongs to the triphenylmethane group and is a common environmental pollutant that threatens non-target organisms. We report the potential of the early colonizing marine bacterium Pseudomonas sp. ESPS40 isolated from the Arabian Sea, India, to decolorize malachite green (MG). The bacterium ESPS40 exhibited a higher ability for MG degradation (86-88%) at varying NaCl concentrations (1-3%). The highest MG degradation (~ 88%) was observed at 1% NaCl. The bacterial strain ESPS40 showed degradation up to 800 mg L^-1 MG. Further, enzyme activities such as tyrosinase (63.48-526.52 U L^-1) and laccase (3.62-28.20 U L^-1) were also analyzed with varying concentrations (100 mg L^-1-1000 mg L^-1) of MG during the degradation process. The dye degradation was confirmed by Fourier transform infrared spectroscopy (FTIR) and high-performance liquid chromatography (HPLC). The outcome of the present study demonstrated Pseudomonas sp. ESPS40 as a potential strain for the efficient degradation of MG at higher concentrations. Thus, Pseudomonas sp. ESPS40 can be utilized as a potential candidate for the biodegradation of MG in wastewater treatment.

Dynamics of the role of LacMeta laccase in the complete degradation and detoxification of malachite green

Laccases highlight for xenobiotic bioremediation, as well as application in the fine chemical, textile, biofuel and food industries. In a previous work, we described the preliminary characterization of laccase LacMeta, a promising enzyme for the bioremediation of dyes, able to decolorization malachite green (MG), trypan blue, methylene blue. Here we demonstrate that LacMeta is indeed suitable for the complete degradation and detoxification of MG dye, not just for its discoloration, since some works show false positives due to the formation of colorless intermediates such as leucomalachite. The optimal pH and temperature parameters of LacMeta were 5.0 and 50 °C, respectively (MG as substrate). LacMeta was tolerant of up to 10 mmol L^- 1 EDTA (82%) and up to 5% (V/V) acetone (91%) and methanol (71%), while SDS promoted severe inhibition. For ions, a high tolerance to cobalt, zinc, manganese, and calcium (10 mmol L^- 1) was also observed (> 90%). Even under high-salinity conditions (1 mol L^- 1 NaCl), the residual bleaching activity of the dye remained at 61%. Furthermore, the bleaching product of MG did not inhibit the germination of sorghum and tomato seeds and was inert to the vegetative structures of the germinated seedlings. Additionally, this treatment effectively reduced the cytotoxic effect of the dye on microorganisms (Escherichia coli and Azospirillum brasilense), which can be explained by H-NMR spectral analysis results since LacMeta completely degraded the peak signals corresponding to the aromatic rings in the dye, demonstrating extreme efficiency in the bioremediation of the xenobiotic at high concentrations (50 mg L^- 1).

Co-metabolic biodegradation of structurally discrepant dyestuffs by Klebsiella sp. KL-1: A molecular mechanism with regards to the differential responsiveness

In this study, an attempt was made to decipher the underlying differential response mechanism of Klebsiella sp. KL-1 induced by exposure to disparate categories of dyestuffs in xylose (Xyl) co-metabolic system. Here, representative reactive black 5 (RB5), remazol brilliant blue R (RBBR) and malachite green (MG) belonging to the azo, anthraquinone and triphenylmethane categories were employed as three model dyestuffs. Klebsiella sp. KL-1 enabled nearly 98%, 80% or 97% removal of contaminants in assays Xyl + RB5, Xyl + RBBR or Xyl + MG after 48 h, which was respectively 16%, 11% or 22% higher than those in the assays devoid of xylose. LC-QTOF-MS revealed an increased formation of smaller molecular weight intermediates in assay Xyl + RB5, whereas more metabolic pathways were deduced in assay Xyl + RBBR. Metaproteomics analysis displayed remarkable proteome alteration with regards to the structural difference effect of dyestuffs by Klebsiella sp. KL-1. Significant (p-value<0.05) activation of pivotal candidate NADH-quinone oxidoreductase occurred after 48 h of disparate dyestuff exposure but with varying abundance. Dominant FMN-dependent NADH-azoreductase, Cytochrome d terminal oxidase or Thiol peroxidase were likewise deemed to be responsible for the catalytic cleavage of RB5, RBBR or MG, respectively. Further, the differential response mechanism towards the structurally discrepant dyestuffs was put forward. Elevated reducing force associated with the corresponding functional proteins/enzymes was transferred to the exterior of the cell to differentially decompose the target contaminants. Overall, this study was dedicated to provide in-depth insights into the molecular response mechanism of co-metabolic degradation of refractory and structurally discrepant dyestuffs by an indigenous isolated Klebsiella strain.

Microbial approaches for sustainable remediation of dye-contaminated wastewater: a review

The coloured effluents produced from different industries, such as textile, plastics, printing, cosmetics, leather and paper, are extremely toxic and a tremendous threat to the aquatic organisms and human beings. The removal of coloured dye pollutants from the aqueous environment is a great challenge and a pressing task. The growing demand for low-cost and efficient treatment approaches has given rise to alternative and eco-friendly methods, such as biodegradation and microbial remediation. This work summarizes the overview and current research on the remediation of dye pollutants from the aqueous environment by microbial bio-sorbents, such as bacteria, fungi, algae, and yeast. In addition, dye degradation capabilities of microbial enzymes have been highlighted and discussed. Further, the influence of various experimental parameters, such as temperature, pH, and concentrations of nutrients, and dye, has been summarized. The proposed mechanism for dye removal by microorganisms is also discussed. The object of this review is to provide a state-of-the-art of microbial remediation technologies in eliminating dye pollutants from water resources.

Engineering globins for efficient biodegradation of malachite green: two case studies of myoglobin and neuroglobin

Engineered globins such as H64D Mb and A15C/H64D Ngb were efficient in the degradation of malachite green, with activities much higher than those of some native enzymes.

Effects of Adding Laccase to Bacterial Consortia Degrading Heavy Oil

High-efficiency bioremediation technology for heavy oil pollution has been a popular research topic in recent years. Laccase is very promising for the remediation of heavy oil pollution because it can not only convert bio-refractory hydrocarbons into less toxic or completely harmless compounds, but also accelerate the biodegradation efficiency of heavy oil. However, there are few reports on the use of laccase to enhance the biodegradation of heavy oil. In this study, we investigated the effect of laccase on the bacterial consortia degradation of heavy oil. The degradation efficiencies of bacterial consortia and the laccase-bacterial consortia were 60.6 ± 0.1% and 68.2 ± 0.6%, respectively, and the corresponding heavy oil degradation rate constants were 0.112 day−1 and 0.198 day−1, respectively. The addition of laccase increased the heavy oil biodegradation efficiency (p < 0.05) and biodegradation rate of the bacterial consortia. Moreover, gas chromatography–mass spectrometry analysis showed that the biodegradation efficiencies of the laccase-bacterial consortia for saturated hydrocarbons and aromatic hydrocarbons were 82.5 ± 0.7% and 76.2 ± 0.9%, respectively, which were 16.0 ± 0.3% and 13.0 ± 1.8% higher than those of the bacterial consortia, respectively. In addition, the degradation rate constants of the laccase-bacterial consortia for saturated hydrocarbons and aromatic hydrocarbons were 0.267 day−1 and 0.226 day−1, respectively, which were 1.07 and 1.15 times higher than those of the bacterial consortia, respectively. The degradation of C15 to C35 n-alkanes and 2 to 5-ring polycyclic aromatic hydrocarbons by laccase-bacterial consortia was higher than individual bacterial consortia. It is further seen that the addition of laccase significantly improved the biodegradation of long-chain n-alkanes of C22–C35 (p < 0.05). Overall, this study shows that the combination of laccase and bacterial consortia is an effective remediation technology for heavy oil pollution. Adding laccase can significantly improve the heavy oil biodegradation efficiency and biodegradation rate of the bacterial consortia.

Heterologous expression of bacterial CotA-laccase, characterization and its application for biodegradation of malachite green

Malachite green (MG) is used as fungicide/parasiticide in aquaculture, its persistence is detrimental as it exhibits carcinogenic effects to aquatic organisms. Bacterial laccase evaluated as the best enzyme at extreme condition for aquatic MG removal. Study aims to increase laccase concentration, CotA-laccase from Bacillus subtilis was cloned and overexpressed in Escherichia coli. Optimal catalysis for purified CotA-laccase were at pH 5.0, 60 °C, and 1 mM of (2,2-azino-di-[3-ethylbenzothiazoline-sulphonate-(6)]) with Km and Kcat 0.087 mM and 37.64 S^-1 respectively. MG biodegradation by CotA-laccase in clam and tilapia pond wastewaters and cytotoxic effect of biodegraded products in grouper fin-1 cells were determined. MG degradation by CotA-laccase was equally efficient, exhibiting upto 90-94% decolorization at freshwater and saline conditions and treated solution was non-toxic to GF-1 cells. Thus, recombinant-CotA-laccase could be an environmentally-friendly enzyme for aquaculture to remove MG, thereby effective to reduce its accumulation in aquatic organisms and ensuring safe aquaculture products.

Efficient biodegradation of malachite green by an artificial enzyme designed in myoglobin

Synthetic dyes such as malachite green (MG) have a wide range of applications. Meanwhile, they bring great challenges for environmental security and cause potential damages to human health. Compared with traditional approaches, enzymatic catalysis is an emerging technique for wastewater treatment. As alternatives to natural enzymes, artificial enzymes have received much attention for potential applications. In previous studies, we have rationally designed artificial enzymes based on myoglobin (Mb), such as by introducing a distal histidine (F43H mutation) and creating a channel to the heme pocket (H64A mutation). We herein show that the artificial enzyme of F43H/H64A Mb can be successfully applied for efficient biodegradation of MG under weak acid conditions. The degradation efficiency is much higher than those of natural enzymes, such as dye-decolorizing peroxidase and laccase (13-18-fold). The interaction of MG and F43H/H64A Mb was investigated by using both experimental and molecular docking studies, and the biodegradation products of MG were also revealed by UPLC-ESI-MS analysis. Based on these results, we proposed a plausible biodegradation mechanism of MG. With the high-yield of overexpression in E. coli cells, this study suggests that the artificial enzyme has potential applications in the biodegradation of MG in fisheries and textile industries.

Comparison of three palm tree peroxidases expressed by Escherichia coli: Uniqueness of African oil palm peroxidase

Palm tree peroxidase has greater catalytic activity, stability and broad application prospects in comparison with horseradish peroxidase. However, slow growth, ecological destruction and high costs prohibit isolation of native peroxidases directly from palm trees. Bioreactor production of palm tree peroxidases would therefore be preferred to overcome such production limitations. Comparison of different recombinant glycan-free palm tree peroxidases would allow understanding the criticality of total glycans to the functions and characteristics. In the present study, African oil palm tree peroxidase expressed by Escherichia coli showed similar stability and 30-100-fold greater activity than that of recombinant royal palm tree peroxidases, but both of their comprehensive indexes were superior to the commercial, native horseradish peroxidase. Recombinant Chamaerops excelsa peroxidase showed no activity possibly due to incorrect protein folding. The results confirmed that recombinant expression by E. coli is potentially an effective means to obtain a mass of palm peroxidases with high activity and stability.

Enhancing the decolorization activity of Bacillus pumilus W3 CotA-laccase to Reactive Black 5 by site-saturation mutagenesis

Reactive Black 5 (RB5) is a typical refractory azo dye. Widespread utilization of RB5 has caused a variety of environmental and health problems. The enzymatic degradation of RB5 can be a promising solution due to its superiority as an eco-friendly and cost-competitive process. Bacterial CotA-laccase shows great application prospect to eliminate hazardous dyes from wastewater. However, efficient decolorization of RB5 CotA-laccase generally requires the participation of costly, toxic mediators. In the present study, we modified the amino acids Thr415 and Thr418 near the type 1 copper site and the amino acid Gln442 at the entrance of the substrate-binding pocket of Bacillus pumilus W3 CotA-laccase to boost its RB5 decolorization activity based on molecular docking analysis and site-saturation mutagenesis. Through the strategies, two double site mutants T415D/Q442A and T418K/Q442A obtained demonstrated 43.94 and 52.64% RB5 decolorization rates in the absence of a mediator at pH 10.0, respectively, which were about 3.70- and 4.43-fold higher compared with the wild-type CotA-laccase. Unexpectedly, the catalytic efficiency of the T418K/Q442A to ABTS was enhanced by 5.33-fold compared with the wild-type CotA-laccase. The mechanisms of conferring enhanced activity to the mutants were proposed by structural analysis. In summary, the mutants T415D/Q442A and T418K/Q442A have good application potentials for the biodegradation of RB5. KEY POINTS: • Three amino acids of CotA-laccase were manipulated by site-saturation mutagenesis. • Decolorization rate of two mutants to RB5 was enhanced 3.70- and 4.43-fold, respectively. • The mechanisms of awarding enhanced activity to the mutants were supposed.