Crosslinked Enzyme Aggregates (CLEAs) of Laccases from Pleurotus citrinopileatus Induced in Olive Oil Mill Wastewater (OOMW)

A systematic study on the characteristics and applications of laccases produced by fungi: insights on their potential for biotechnologies

Laccases are polyphenol oxidase enzymes and form the enzyme complex known for their role in wood decomposition and lignin degradation. The present study aimed to systematically review the state-of-the-art trends in scientific publications on laccase enzymes of the last 10 years. The main aspects checked included the laccase-producing fungal genera, the conditions of fungal growth and laccase production, the methods of immobilization, and potential applications of laccase. After applying the systematic search method 177 articles were selected to compound the final database. Although various fungi produce laccase, most studies were Trametes and Pleurotus genera. The submerged fermentation (SmF) has been the most used, however, the use of solid-state fermentation (SSF) appeared as a promising technique to produce laccase when using agro-industrial residues as substrates. Studies on laccase immobilization showed the covalent bonding and entrapment methods were the most used, showing greater efficiency of immobilization and a high number of enzyme reuses. The main use of the laccase was in bioremediation, especially in the discoloration of dyes from the textile industry and the degradation of pharmaceutical waste. Implications and consequences of all these findings in biotechnology and environment, as well as the trends and gaps of laccase research were discussed.

Immobilizing white-rot fungi laccase: Toward bio-derived supports as a circular economy approach in organochlorine removal

Despite their high persistence in the environment, organochlorines (OC) are widely used in the pharmaceutical industry, in plastics, and in the manufacture of pesticides, among other applications. These compounds and the byproducts of their decomposition deserve attention and efficient proposals for their treatment. Among sustainable alternatives, the use of ligninolytic enzymes (LEs) from fungi stands out, as these molecules can catalyze the transformation of a wide range of pollutants. Among LEs, laccases (Lac) are known for their efficiency as biocatalysts in the conversion of organic pollutants. Their application in biotechnological processes is possible, but the enzymes are often unstable and difficult to recover after use, driving up costs. Immobilization of enzymes on a matrix (support or solid carrier) allows recovery and stabilization of this catalytic capacity. Agricultural residual biomass is a passive environmental asset. Although underestimated and still treated as an undesirable component, residual biomass can be used as a low-cost adsorbent and as a support for the immobilization of enzymes. In this review, the adsorption capacity and immobilization of fungal Lac on supports made from residual biomass, including compounds such as biochar, for the removal of OC compounds are analyzed and compared with the use of synthetic supports. A qualitative and quantitative comparison of the reported results was made. In this context, the use of peanut shells is highlighted in view of the increasing peanut production worldwide. The linkage of methods with circular economy approaches that can be applied in practice is discussed.

An Overview of Crosslinked Enzyme Aggregates: Concept of Development and Trends of Applications

Enzymes are commonly used as biocatalysts for various biological and chemical processes in industrial applications. However, their limited operational stability, catalytic efficiency, poor reusability, and high-cost hamper further industrial usage. Thus, crosslinked enzyme aggregates (CLEAs) are developed as a better enzyme immobilization tool to extend the enzymes' operational stability. This immobilization method is appealing because it is simpler due to the absence of ballast and permits the collective use of crude enzyme cocktails. CLEAs, so far, have been successfully developed using a variety of enzymes, viz., hydrolases, proteases, amidases, lipases, esterases, and oxidoreductase. Recent years have seen the emergence of novel strategies for preparing better CLEAs, which include the combi- and multi-CLEAs, magnetics CLEAs, and porous CLEAs for various industrial applications, viz., laundry detergents, organic synthesis, food industries, pharmaceutical applications, oils, and biodiesel production. To better understand the different strategies for CLEAs' development, this review explores these strategies and highlights the relevant concerns in designing innovative CLEAs. This article also details the challenges faced during CLEAs preparation and solutions for overcoming them. Finally, the trending strategies to improve the preparation of CLEAs alongside their industrial application trends are also discussed.

Innovative biocatalyst synthesis of pectinolytic enzymes by cross-linking strategy: Potentially immobilised pectinases for the production of pectic-oligosaccharides from pectin

Pectinases are outstanding multienzymes, which have the potential to produce new emerging pectic-oligosaccharides (POS) via enzymatic hydrolysis of pectin. However, free pectinase is unable to undergo repeated reaction for the production of POS. This study proposed a sustainable biocatalyst of pectinases known as cross-linked pectinase aggregates (CLPA). Pectinase from Aspergillus aculeatus was successfully precipitated using 2 mg/mL pectinase and 60 % acetone for 20 min at 20 °C, which remained 36.3 % of its initial activity. The prepared CLPA showed the highest activity recovery (85.0 %), under the optimised conditions (0.3 % (v/v) starch and glutaraldehyde mixture (St/Ga), 1.5: 1 of St/Ga, 25 °C, 1.5 h). Furthermore, pectin-degrading enzymes from various sources were used to produce different CLPA. The alteration of pectinase secondary structure gave high stability in acidic condition (pH 4), thermostability, deactivation energy and half-life, and improved storage stability at 4 °C for 30 days. Similarly to their free counterpart, the CLPA exhibited comparable enzymatic reaction kinetics and could be reused eight times with approximately 20 % of its initial activity. The developed CLPA does not only efficaciously produced POS from pectin as their free form, but also exhibited better operational stability and reusability, making it more suitable for POS production.

2,4-Dichlorophenol biotransformation using immobilized marine halophilic Bacillus subtilis culture and laccase enzyme: application in wastewater treatment

Background

2,4-Dichlorophenol (2,4-DCP) is a very toxic aromatic compound for humans and the environment and is highly resistant to degradation. Therefore, it is necessary to develop efficient remediation and cost-effective approaches to this pollutant. Microbial enzymes such as laccases can degrade phenols, but limited information is known about immobilized bacterial laccase and their reuse.

Methods

Immobilization of marine halophilic Bacillus subtilis AAK cultures via entrapment and adsorption techniques and degradation of different phenolic compounds by immobilized cells were estimated. Partial purification and immobilization of laccase enzymes were carried out. In addition, the biodegradation of 2,4-DCP and others contaminated by wastewater was investigated.

Results

Immobilization of cells and partially purified laccase enzymes by adsorption into 3% alginate increased 2,4-DCP biotransformation compared with free cells and free enzymes. In addition, the reuse of both the immobilized culture and laccase enzymes was evaluated. The highest removal of 2,4-DCP from pulp and paper wastewater samples inoculated by immobilized cells and the immobilized enzyme was 90% and 95%, respectively, at 50 h and 52 h of incubation, compared to free cells and free enzyme.

Conclusion

The results of this study have revealed the immobilization of a biocatalyst and its laccase enzyme as a promising technique for enhancing the degradation of 2,4-DCP and other toxic phenolic and aromatic compounds. The reuse of the biocatalyst and its laccase enzyme enabled the application of this cost-effective bioremediation strategy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00417-1.

Insolubilization of Tramates versicolor laccase as cross-linked enzyme aggregates for the remediation of trace organic contaminants from municipal wastewater

The novelty of this study deals with the biocatalytic treatment of trace organic contaminants (TrOCs) from municipal wastewater by insolubilized laccase. Laccase from Trametes versicolor was aggregated by three-phase partitioning technique followed by cross-linking with glutaraldehyde to produce insolubilized laccase as cross-linked enzyme aggregates (CLEAs). The optimal conditions for CLEAs preparation include ammonium sulphate concentration of 83% (w/v), crude to t-butanol ratio of 1.00: 1.05 (v/v), pH 5.3, and glutaraldehyde concentration of 20 mM obtained via statistical design. The efficiency of insolubilization of the CLEAs laccase based on the k_cat/k_m ratio was approximately 4.8-fold greater than that of free laccase. The developed CLEAs showed greater resistance to product inhibition mediated by ABTS than the free enzyme and exhibited excellent catalytic activity even after the tenth successive cycle. Further, free laccase and the synthesized CLEAs laccase were utilized to treat five analgesics, two NSAIDS, three antibiotics, two antilipemics, and three pesticides in the municipal wastewater. Under the batch process with operating conditions of pH 7.0 and 20 °C, 1000 U/L of CLEAs, laccase removed 11 TrOCs in the range of about 20-99%. However, the inactivated CLEAs only adsorbed 2-25% of TrOCs. It was observed that acetaminophen, mefenamic acid, trimethoprim, and metolachlor depicted almost complete removal with CLEAs laccase. The performance of CLEAs laccase in a perfusion basket reactor was tested for the removal of TrOCs from municipal wastewater.

Cross-linked enzyme aggregates immobilization: preparation, characterization, and applications

Enzymes are commonly used as biocatalysts for various biological and chemical processes. However, some major drawbacks of free enzymes (e.g. poor reusability and instability) significantly restrict their industrial practices. How to overcome these weaknesses remain considerable challenges. Enzyme immobilization is one of the most effective ways to improve the reusability and stability of enzymes. Cross-linked enzyme aggregates (CLEAs) has been known as a novel and versatile carrier-free immobilization method. CLEAs is attractive due to its simplicity and robustness, without purification. It generally shows: high catalytic specificity and selectivity, good operational and storage stabilities, and good reusability. Moreover, co-immobilization of different kinds of enzymes can be acquired. These CLEAs advantages provide opportunities for further industrial applications. Herein, the preparation parameters of CLEAs were first summarized. Next, characterization of structural and catalytic properties, stability and reusability are also proposed. Finally, some important applications of this technique in: environmental protection, industrial chemistry, food industry, and pharmaceutical synthesis and delivery are introduced. Potential challenges and future research directions, such as improving cross-linking efficiency and internal mass transfer efficiency, are also presented. This implies that CLEAs provide an efficient and feasible technique to improve the properties of enzymes for use in the industry.

Carrier-Free Cross-linked Laccase Crystals for Biocatalytic Degradation of Textile Industrial Effluents

Herein, laccase from Trametes versicolor was used to fabricate carrier-free cross-linked laccase crystals (CLLCs) and deployed as a robust catalyst for waste effluent treatment. The surface morphology and involvement of functional group attributes of CLLCs were scrutinized by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). As fabricated CLLCs were subjected to kinetic characterization by assessing the effects of pH environment, thermal profile, and substrate (determination of K_m and V_max) on the activity. A fully characterized CLLCs fraction was used to treat synthetic dyes containing waste effluents taken from various industries, i.e., Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills. Degradation profile revealed 36.8%, 27.6%, 39.9%, and 26.4% degradation of Chenab Textile Industry, M-tax, Sitara, and National Silk & Rayon Mills, respectively, by the free form of laccase, whereas the biocatalytic activity of CCLCs led to 78.6%, 75.6%, 85.5%, and 63.3% degradation of those effluents. The decrease in peak and mass region alongside the presence of new peaks in GC-MS affirms the effective decolorization of contaminated waste effluents. CLLCs retained over 70% and 50% of their degradation activity after 3 and 5 cycles, respectively. In conclusion, CLLCs might represent a robust bioprocess to improve the usability of laccase for various synthetic dyes containing waste effluents to diminish environmental pollution from the dye-based industries.

Laccases as green and versatile biocatalysts: from lab to enzyme market-an overview

Laccases are multi-copper oxidase enzymes that catalyze the oxidation of different compounds (phenolics and non-phenolics). The scientific literature on laccases is quite extensive, including many basic and applied research about the structure, functions, mechanism of action and a variety of biotechnological applications of these versatile enzymes. Laccases can be used in various industries/sectors, from the environmental field to the cosmetics industry, including food processing and the textile industry (dyes biodegradation and synthesis). Known as eco-friendly or green enzymes, the application of laccases in biocatalytic processes represents a promising sustainable alternative to conventional methods. Due to the advantages granted by enzyme immobilization, publications on immobilized laccases increased substantially in recent years. Many patents related to the use of laccases are available, however, the real industrial or environmental use of laccases is still challenged by cost-benefit, especially concerning the feasibility of producing this enzyme on a large scale. Although this is a compelling point and the enzyme market is heated, articles on the production and application of laccases usually neglect the economic assessment of the processes. In this review, we present a description of laccases structure and mechanisms of action including the different sources (fungi, bacteria, and plants) for laccases production and tools for laccases evolution and prediction of potential substrates. In addition, we both compare approaches for scaling-up processes with an emphasis on cost reduction and productivity and critically review several immobilization methods for laccases. Following the critical view on production and immobilization, we provide a set of applications for free and immobilized laccases based on articles published within the last five years and patents which may guide future strategies for laccase use and commercialization.

Laccase-mediated delignification and detoxification of lignocellulosic biomass: removing obstacles in energy generation

The rising global population and worldwide industrialization have led to unprecedented energy demand that is causing fast depletion of fossil reserves. This has led to search for alternative energy sources that are renewable and environment friendly. Use of lignocellulosic biomass for energy generation is considered a promising approach as it does not compete with food supply. However, the lignin component of the biomass acts as a natural barrier that prevents its efficient utilization. In order to remove the lignin and increase the amount of fermentable sugars, the lignocellulosic biomass is pretreated using physical and chemical methods which are costly and hazardous for environment. Moreover, during the traditional pretreatment process, numerous inhibitory compounds are generated that adversely affect the growth of fermentative microbes. Alternatively, biological methods that use microbes and their enzymes disrupt lignin polymers and increase the accessibility of the carbohydrates for the sugar generation. Microbial laccases have been considered as an efficient biocatalyst for delignification and detoxification offering a green initiative for energy generation process. The present review aims to bring together recent studies in bioenergy generation using laccase biocatalyst in the pretreatment processes. The work provides an overview of the sustainable and eco-friendly approach of biological delignification and detoxification through whole-cell and enzymatic methods, use of laccase-mediator system, and immobilized laccases for this purpose. It also summarizes the advantages, associated challenges, and potential prospects to overcome the limitations.

Available Pathways for Operationalizing Circular Economy into the Olive Oil Supply Chain: Mapping Evidence from a Scoping Literature Review

Circular economy (CE) is increasingly seen as a promising paradigm for transitioning agri-food systems towards more sustainable models of production and consumption, enabling virtuous and regenerative biological metabolisms based on strategies of eco-efficiency and eco-effectiveness. This contribution seeks to provide a theoretical and empirical framework for operationalizing the CE principles into the olive oil supply chain, that plays a central role in the agroecological systems of the Mediterranean region. A scoping literature review has been conducted in order to identify the available pathways so far explored by scholars for reshaping the olive oil supply chain from a circular perspective. The analyzed literature has been charted on the base of the circular pathway examined, and according to the supply chain subsystem(s) to which it refers. Results are discussed highlighting the main issues, the technology readiness level of the available pathways, the prevailing approaches and knowledge gaps. A synthetic evidence map is provided, framing visually the scrutinized pathways into the Ellen MacArthur Foundation’s CE ‘butterfly’ graph. The work is intended to be a valuable baseline for inquiring how circularity can be advanced in the specific supply chain of olive oil, and which are the strategic opportunities, as well as the barriers to overcome, in order to foster the transition.

From Enzyme Stability to Enzymatic Bioelectrode Stabilization Processes

Bioelectrocatalysis using redox enzymes appears as a sustainable way for biosensing, electricity production, or biosynthesis of fine products. Despite advances in the knowledge of parameters that drive the efficiency of enzymatic electrocatalysis, the weak stability of bioelectrodes prevents large scale development of bioelectrocatalysis. In this review, starting from the understanding of the parameters that drive protein instability, we will discuss the main strategies available to improve all enzyme stability, including use of chemicals, protein engineering and immobilization. Considering in a second step the additional requirements for use of redox enzymes, we will evaluate how far these general strategies can be applied to bioelectrocatalysis.