Biocatalytic characterization of free and immobilized laccase from Trametes versicolor in its activation zone

Deciphering ligninolytic enzymes in the secretome of Pycnoporus sp. and their potential in degradation of 2-chlorophenol

Chlorophenols and their derivatives are persistent environmental pollutants, posing a threat to terrestrial and aquatic life. The biological approach for eliminating toxic contaminants is an effective, sustainable, and environmental friendly method. In this study, the crude enzymes present in the secretome of white-rot fungus (Pycnoporus sp.) were explored for the degradation of 2-chlorophenol. The activity of ligninolytic enzymes in the secretome was analyzed and characterized for their kinetics and thermodynamic properties. Laccase and manganese peroxidase were prevalent ligninolytic enzymes and exhibited temperature stability in the range of 50-65 °C and pH 4-5, respectively. The kinetic parameters Michaelis constant (Km) and turnover number (Kcat) for Lac were 42.54 μM and 45 s-1 for 2,2'-azino-bis (3-ethylben- zothiazoline-6-sulfonic acid), and 93.56 μM and 48 s-1 towards 2,6-dimethoxyphenol whereas Km and Kcat for MnP were 2039 μM and 294 s-1 for guaiacol as substrate. Treatment with the crude enzymes laccase and manganese peroxidase results in the reduction of 2-chlorophenol concentration, confirmed by UV-visible absorption spectra and high-performance liquid chromatography analysis. The detoxification of 2-chlorophenol into less toxic forms was confirmed by the plate toxicity assay. This study demonstrated that crude enzymes produced by Pycnoporus sp. could potentially minimize the toxicity of phenolic compounds in a sustainable way.

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.

Encapsulated laccase in bimetallic Cu/Zn ZIFs as stable and reusable biocatalyst for decolorization of dye wastewater

Laccase have received extensive attention in pollutant degradation, but its practical viability is largely affected by the poor stability, easy inactivation and difficulty in recycling for the present. Enzyme immobilization offers enhanced enzyme stability and constructs a synergistic system for the efficient adsorption and degradation of pollutants. In this study, bimetallic Cu/Zn ZIFs were synthesized by co-precipitation method as the protective carrier for laccase. Lac@Cu-ZIF-90 exhibited a good protective effect on laccase and showed a high operational stability in various interfering environments. Free laccase was completely inactivated at pH 7.0 but Lac@Cu-ZIF-90 could maintain 50.0 % activity. Benefiting from the encapsulation of laccase and porous structure of Cu-ZIF-90, the Lac@Cu-ZIF-90 exhibited decolorization efficiency for dye wastewater. More importantly, the Lac@Cu-ZIF-90 could be recovered from the dye solution and re-used to adsorb and degrade the synthetic dye for multiple times, its removal rate for reactive deep green was only decreased about 10.8 % after five cycles. This work reveals that the Cu-ZIF-90 provides a favorable environment for laccase and as a protective layer to relieve the conformation change, which provides an efficient strategy to decolorize dye wastewater. Therefore, Cu-ZIF-90 promises applications as enzymes encapsulation has great potential in water remediation.

Zeolitic imidazolate frameworks as effective crystalline supports for aspergillus-based laccase immobilization for the biocatalytic degradation of carbamazepine

In this study, zeolitic imidazolate frameworks (ZIF) were employed as effective porous supports for laccase enzyme attachment and further explored synergistic adsorption and biocatalytic degradation of carbamazepine (CBZ) in aqueous solutions. Characterization results from FTIR and NMR analysis confirmed successful incorporation of the laccase enzyme onto ZIF particles. Further analyses from SEM and TEM revealed rhombic dodecahedral morphologies of ZIF crystals with crusts of the enzyme observed on the particles' surface. The carbamazepine degradation results showed that immobilization of the laccase improved its stability and resistance at various pH's, in comparison to the free enzyme. The immobilized laccase also exhibited relatively higher activities across the studied temperature range compared to the free form. Kinetic studies revealed a negligible decline in velocity, Vmax after immobilization, evaluated to be 0.873 and 0.692 mg L-1 h-1 for the free and immobilized laccase, respectively. The immobilized laccase demonstrated improved stabilities towards organic solvents, which qualifies the composite's application in real wastewater samples. In which case, the laccase-ZIF composite proved effective in CBZ decontamination with an efficiency of ∼92%. Furthermore, the immobilized laccase exhibited appreciable storage stabilities (∼70% residual activity) for up to 15 days before any significant loss in activity.

Inhibition mechanisms of Fe2+/Fe3+ and Mn2+ on fungal laccase-enabled bisphenol a polyreaction

Bisphenol A (BPA) is regarded as an endocrine disruptor associated with negative health effects in animals and humans. Laccase from white-rot fungus can enable BPA oxidation and auto-polymerization to circumvent its biotoxicity, but the work concerning the effect mechanisms of divalent and trivalent metal ions (MIs) on BPA polyreaction have rarely been reported. Herein, Trametes versicolor laccase-started BPA conversion within 1 h followed pseudo-first order kinetics, and the rate constant (k_prcs) and half-life were respectively 0.61 h^-1 and 1.14 h. The presence of Ca²⁺, Mg²⁺, Cu²⁺, Pb²⁺, Cd²⁺, Zn²⁺ and Al³⁺ exhibited insignificant impact on BPA removal, whereas Fe²⁺, Fe³⁺ and Mn²⁺ had a strong inhibiting effect. Compared with MI-free, the k_prcs values of BPA respectively lowered 34.4%, 44.3% and 98.4% in the presence of Fe²⁺, Fe³⁺ and Mn²⁺. Enzymatic activity and differential absorption spectrum disclosed that the inhibitory actions were accomplished by two different mechanisms. One is Fe²⁺ was preferentially oxidized into Fe³⁺ that restrained laccase activity at the initial stage of reaction, and subsequently, the formed Fe³⁺ complex bound with laccase T1-Cu site and thus impeded the single-electron transfer system. The other is Mn²⁺ was instantly oxidized by laccase to generate Mn³⁺-citrate complex, which completely consumed the dissolved O₂ in solution and consequently terminated BPA removal. Considering environmental bioremediation, T. versicolor laccase-enabled auto-polymerization is a simple and convenient candidate to eliminate BPA in enzymatic wastewater treatment, however the effects of Fe²⁺/Fe³⁺ and Mn²⁺ on BPA decontamination should be cautiously assessed.

Diversity of Wood-Decaying Fungi in Wuliangshan Area, Yunnan Province, P.R. China

Five surveys were carried out in the Wuliangshan area, Yunnan Province, P.R. China, based on a combination of morphological features and molecular evidence. Around 2454 specimens of wood-decaying fungi were collected. The paper summarizes the obtained results on the wood-decaying fungi of this area, consisting in 95 species distributed in 59 genera, 23 families and 9 orders. Their hosts and substrates were also identified. A checklist of wood-decaying fungi is given. Sequences of the ITS nrRNA gene region of the studied specimens were generated and phylogenetic analysis was performed with maximum likelihood, maximum parsimony and Bayesian inference methods. The present list of wood-decaying fungi enriches the knowledge of fungal diversity worldwide and supplies the basic data for future applications.

Overview of Recent Advances in Immobilisation Techniques for Phenol Oxidases in Solution

Over the past two decades, phenol oxidases, particularly laccases and tyrosinases, have been extensively used for the removal of numerous pollutants in wastewaters due to their broad substrate specificity and their ability to use readily accessible molecular oxygen as the essential cofactor. As for other enzymes, immobilisation of laccases and tyrosinases has been shown to improve the performance and efficiency of the biocatalysts in solution. Several reviews have addressed the enzyme immobilisation techniques and the application of phenol oxidases to decontaminate wastewaters. This paper offers an overview of the recent publications, mainly from 2012 onwards, on the various immobilisation techniques applied to laccases and tyrosinases to induce and/or increase the performance of the biocatalysts. In this paper, the emphasis is on the efficiencies achieved, in terms of structural modifications, stability and resistance to extreme conditions (pH, temperature, inhibitors, etc.), reactivity, reusability, and broad substrate specificity, particularly for application in bioremediation processes. The advantages and disadvantages of several enzyme immobilisation techniques are also discussed. The relevance and effectiveness of the immobilisation techniques with respect to wastewater decontamination are critically assessed. A perspective on the future directions for large-scale application of the phenol oxidases in immobilised forms is provided.

Processing and modification of hydrogel and its application in emerging contaminant adsorption and in catalyst immobilization: a review

Due to the wonderful property of hydrogels, they can provide a platform for a wide range of applications. Recently, there is a growing research interest in the development of potential hydrogel adsorbents in wastewater treatment due to their adsorption ability toward aqueous pollutants. It is important to prepare such a hydrogel that possesses appropriate robustness, adsorption capacity, and adsorption efficiency to meet the need of water treatment. In order to improve the property of hydrogels, much effort has been made by researchers to modify hydrogels, among which incorporating inorganic components into the polymeric networks is the most common method, which can reduce the product cost and simplify the preparation procedure. Not only can hydrogel be applied as adsorbent, but it also can be used as matrix for catalyst immobilization. In this review, the key advancement on the preparation and modification of hydrogels is discussed, with special emphasis on the introduction of inorganic materials into polymeric networks and consequential changes in the properties of mechanical strength, swelling, and adsorption. Besides, hydrogels used as adsorbents for removal of dyes and inorganic pollutants have been widely explored, but their use for adsorbing emerging contaminants from aqueous solution has not received much attention. Thus, this review is mainly focused on hydrogels' application in removing emerging contaminants by adsorption. Furthermore, hydrogels can be also applied in immobilizing catalysts, such as enzyme and photocatalyst, to remove pollutants completely and avoid secondary pollution, so their progress as catalyst matrix is overviewed.