An Organic Chemist's Guide to Mediated Laccase Oxidation

Use of sawdust for production of ligninolytic enzymes by white-rot fungi and pharmaceutical removal

Use of white-rot fungi for enzyme-based bioremediation of wastewater is of high interest. These fungi produce considerable amounts of extracellular ligninolytic enzymes during solid-state fermentation on lignocellulosic materials such as straw and sawdust. We used pure sawdust colonized by Pleurotus ostreatus, Trametes versicolor, and Ganoderma lucidum for extraction of ligninolytic enzymes in aqueous suspension. Crude enzyme suspensions of the three fungi, with laccase activity range 12-43 U/L and manganese peroxidase activity range 5-55 U/L, were evaluated for degradation of 11 selected pharmaceuticals spiked at environmentally relevant concentrations. Sulfamethoxazole was removed significantly in all treatments. The crude enzyme suspension from P. ostreatus achieved degradation of wider range of pharmaceuticals when the enzyme activity was increased. Brief homogenization of the colonized sawdust was also observed to be favorable, resulting in significant reductions after a short exposure of 5 min. The highest reduction was observed for sulfamethoxazole which was reduced by 84% compared to an autoclaved control without enzyme activity and for trimethoprim which was reduced by 60%. The compounds metoprolol, lidocaine, and venlafaxine were reduced by approximately 30% compared to the control. Overall, this study confirmed the potential of low-cost lignocellulosic material as a substrate for production of enzymes from white-rot fungi. However, monitoring over time in bioreactors revealed a rapid decrease in enzymatic ligninolytic activity.

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.

Eco-friendly TEMPO/laccase/O2 biocatalytic system for degradation of Indigo Carmine: operative conditions and laccase inactivation

The biocatalytic system laccase/TEMPO/O₂ has attracted the attention of researchers over the past two decades. A variety of applications for the system include organic synthesis, modification of cellulose, and oxidative degradation of environmental contaminants. A rigorous and predictable quantitative assessment of the change in enzymatic activity under the influence of a mediator is important for such a system. In this study, the operative conditions for carrying out a model reaction for the degradation of the synthetic dye Indigo Carmine in the presence of Trametes versicolor laccase/TEMPO were determined and the enzyme inactivation under the action of a mediator and substrate was studied. The long-term stability of Trametes versicolor laccase was assessed and the regression model of the response surface of laccase activity under the influence of TEMPO was created. It has been shown that laccase is inactivated in the presence of TEMPO, but the addition of the dye, CuSO₄ or CuCl₂ reduces this effect. The system under study can be used repeatedly for the Indigo Carmine decolorization, however, a gradual falling rate during the process is observed from cycle to cycle. This is due to two reasons - firstly, a decrease in the enzyme activity with each batch and secondly, the consumption of the mediator (22% within 5 days). Relatively high enzyme activity (>40%) is maintained after 73 cycles (1 portion of IC contained 25 μM) using 500 μM TEMPO and 0.12 U mL^-1 laccase. The laccase/TEMPO system has shown its effectiveness in the treatment of artificial wastewater containing high concentrations of Indigo carmine (0.5 g L^-1). In this case, the dye solution becomes 100% colorless within 5 hours in the presence of dye bath components and within 7.5 hours in a buffer solution.

Potential of the enzyme laccase for the synthesis and derivatization of antimicrobial compounds

Laccases [E.C. 1.10.3.2, benzenediol:dioxygen oxidoreductase] can oxidize phenolic substances, e.g. di- and polyphenols, hydroxylated biaryls, aminophenols or aryldiamines. This large substrate spectrum is the basis for various reaction possibilities, which include depolymerization and polymerization reactions, but also the coupling of different substance classes. To catalyze these reactions, laccases demand only atmospheric oxygen and no depletive cofactors. The utilization of mild and environmentally friendly reaction conditions such as room temperature, atmospheric pressure, and the avoidance of organic solvents makes the laccase-mediated reaction a valuable tool in green chemistry for the synthesis of biologically active compounds such as antimicrobial substances. In particular, the production of novel antibiotics becomes vital due to the evolution of antibiotic resistances amongst bacteria and fungi. Therefore, laccase-mediated homo- and heteromolecular coupling reactions result in derivatized or newly synthesized antibiotics. The coupling or derivatization of biologically active compounds or its basic structures may allow the development of novel pharmaceuticals, as well as the improvement of efficacy or tolerability of an already applied drug. Furthermore, by the laccase-mediated coupling of two different active substances a synergistic effect may be possible. However, the coupling of compounds that have no described efficacy can lead to biologically active substances by means of laccase. The review summarizes laccase-mediated reactions for the synthesis of antimicrobial compounds valuable for medical purposes. In particular, reactions with two different reaction partners were shown in detail. In addition, studies with in vitro and in vivo experimental data for the confirmation of the antibacterial and/or antifungal efficacy of the products, synthesized with laccase, were of special interest. Analyses of the structure-activity relationship confirm the great potential of the novel compounds. These substances may represent not only a value for pharmaceutical and chemical industry, but also for other industries due to a possible functionalization of surfaces such as wood or textiles.