Improving the decolorization activity of Bacillus pumilus W3 CotA-laccase to Congo Red by rational modification

Reusable CS-Ca@PEI/CuMnO2 Hydrogel Beads for Peroxymonosulfate-Activated Degradation of Congo Red

Metal oxides can activate peroxymonosulfate (PMS) for the catalytic degradation of organic dyes. However, achieving high catalytic efficiency, structural stability, ease of recovery, and recyclability remains challenging for both research and practical applications. To address these requirements, a bimetallic oxide, CuMnO2, was synthesized using a simple hydrothermal approach and was encapsulated to create hydrogel beads, CS-Ca@PEI/CuMnO2. Subsequently, CS-Ca@PEI/CuMnO2 was used to activate PMS and establish a solid-liquid heterogeneous oxidation system (CS-Ca@PEI/CuMnO2/PMS) for the degradation of Congo red (CR). The effects of various parameters such as different systems, catalyst dosages, initial pH values, PMS concentrations, temperatures, and anion types on the catalytic degradation properties of CS-Ca@PEI/CuMnO2 for CR were systematically evaluated. The results indicated that CS-Ca@PEI/CuMnO2 has exceptional degradation capacity, achieving 91.0% degradation of CR at pH 7. After three degradation cycles, the catalyst maintained an 86.9% degradation efficiency compared to its original performance, highlighting its robust structural stability. The presence of reactive radicals, specifically 1O2 and •O2-, were confirmed through quenching experiments, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance spectroscopy (EPR). Liquid chromatography-tandem mass spectrometry (LC-MS) revealed ten proposed intermediates in the catalytic degradation process. Due to its exceptional catalytic performance, structural durability, recyclability, and ease of retrieval, the catalyst shows great potential for effectively removing organic pollutants from industrial wastewater.

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.

Molecular insights into substrate promiscuity of CotA laccase catalyzing lignin-phenol derivatives

CotA laccases are multicopper oxidases known for promiscuously oxidizing a broad range of substrates. However, studying substrate promiscuity is limited by the complexity of electron transfer (ET) between substrates and laccases. Here, a systematic analysis of factors affecting ET including electron donor acceptor coupling (ΗDA), driving force (ΔG) and reorganization energy (λ) was done. Catalysis rates of syringic acid (SA), syringaldehyde (SAD) and acetosyringone (AS) (kcat(SAD) > kcat(SA) > kcat(AS)) are not entirely dependent on the ability to form phenol radicals indicated by ΔG and λ calculated by Density Functional Theory (SA < SAD ≈ AS). In determined CotA/SA and CotA/SAD structures, SA and SAD bound at 3.9 and 3.7 Å away from T1 Cu coordinating His419 ensuring a similar ΗDA. Abilities of substrate to form phenol radicals could mainly account for difference between kcat(SAD) and kcat(SA). Furthermore, substrate pocket is solvent exposed at the para site of substrate's phenol hydroxyl, which would destabilize binding of AS in the same orientation and position resulting in low kcat. Our results indicated shallow partially covered binding site with propensity of amino acids distribution might help CotA discriminate lignin-phenol derivatives. These findings give new insights for developing specific catalysts for industrial application.

Heterologous expression, purification, and characterization of thermo- and alkali-tolerant laccase-like multicopper oxidase from Bacillus mojavensis TH309 and determination of its antibiotic removal potential

Laccases or laccase-like multicopper oxidases have great potential in bioremediation to oxidase phenolic or non-phenolic substrates. However, their inability to maintain stability in harsh environmental conditions and against non-substrate compounds is one of the main reasons for their limited use. The gene (mco) encoding multicopper oxidase from Bacillus mojavensis TH309 were cloned into pET14b( +), expressed in Escherichia coli, and purified as histidine tagged enzyme (BmLMCO). The molecular weight of the enzyme was about 60 kDa. The enzyme exhibited laccase-like activity toward 2,6-dimethoxyphenol (2,6-DMP), syringaldazine (SGZ), and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS). The highest enzyme activity was recorded at 80 °C and pH 8. BmLMCO showed a half-life of ~ 305, 99, 50, 46, 36, and 20 min at 40, 50, 60, 70, 80, and 90 °C, respectively. It retained more than 60% of its activity after pre-incubation in the range of pH 5-12 for 60 min. The enzyme activity significantly increased in the presence of 1 mM of Cu2+. Moreover, BmLMCO tolerated various chemicals and showed excellent compatibility with organic solvents. The Michaelis constant (Km) and the maximum velocity (Vmax) values of BmLMCO were 0.98 mM and 93.45 µmol/min, respectively, with 2,6-DMP as the substrate. BmLMCO reduced the antibacterial activity of cefprozil, gentamycin, and erythromycin by 72.3 ± 1.5%, 79.6 ± 6.4%, and 19.7 ± 4.1%, respectively. This is the first revealing shows the recombinant production of laccase-like multicopper oxidase from any B. mojavensis strains, its biochemical properties, and potential for use in bioremediation.