Development of a packed bed reactor for the removal of aromatic hydrocarbons from soil using laccase/mediator feeding system

Purification, characterization and three-dimensional structure prediction of multicopper oxidase Laccases from Trichoderma lixii FLU1 and Talaromyces pinophilus FLU12

Broad-spectrum biocatalysts enzymes, Laccases, have been implicated in the complete degradation of harmful pollutants into less-toxic compounds. In this study, two extracellularly produced Laccases were purified to homogeneity from two different Ascomycetes spp. Trichoderma lixii FLU1 (TlFLU1) and Talaromyces pinophilus FLU12 (TpFLU12). The purified enzymes are monomeric units, with a molecular mass of 44 kDa and 68.7 kDa for TlFLU1 and TpFLU12, respectively, on SDS-PAGE and zymogram. It reveals distinct properties beyond classic protein absorption at 270-280 nm, with TlFLU1's peak at 270 nm aligning with this typical range of type II Cu site (white Laccase), while TpFLU12's unique 600 nm peak signifies a type I Cu2+ site (blue Laccase), highlighting the diverse spectral fingerprints within the Laccase family. The Km and kcat values revealed that ABTS is the most suitable substrate as compared to 2,6-dimethoxyphenol, caffeic acid and guaiacol for both Laccases. The bioinformatics analysis revealed critical His, Ile, and Arg residues for copper binding at active sites, deviating from the traditional two His and a Cys motif in some Laccases. The predicted biological functions of the Laccases include oxidation-reduction, lignin metabolism, cellular metal ion homeostasis, phenylpropanoid catabolism, aromatic compound metabolism, cellulose metabolism, and biological adhesion. Additionally, investigation of degradation of polycyclic aromatic hydrocarbons (PAHs) by purified Laccases show significant reductions in residual concentrations of fluoranthene and anthracene after a 96-h incubation period. TlFLU1 Laccase achieved 39.0% and 44.9% transformation of fluoranthene and anthracene, respectively, while TpFLU12 Laccase achieved 47.2% and 50.0% transformation, respectively. The enzyme structure-function relationship study provided insights into the catalytic mechanism of these Laccases for possible biotechnological and industrial applications.

Unraveling the mechanism of interaction: accelerated phenanthrene degradation and rhizosphere biofilm/iron plaque formation influenced by phenolic root exudates

Phenolic root exudates (PREs) secreted by wetland plants facilitate the accumulation of iron in the rhizosphere, potentially providing the essential active iron required for the generation of enzymes that degrade polycyclic aromatic hydrocarbon, thereby enhancing their biodegradation. However, the underlying mechanisms involved are yet to be elucidated. This study focuses on phenanthrene (PHE), a typical polycyclic aromatic hydrocarbon pollutant, utilizing representative PREs from wetland plants, including p-hydroxybenzoic, p-coumaric, caffeic, and ferulic acids. Using hydroponic experiments, 16S rRNA sequencing, and multiple characterization techniques, we aimed to elucidate the interaction mechanism between the accelerated degradation of PHE and the formation of rhizosphere biofilm/iron plaque influenced by PREs. Although all four types of PREs altered the biofilm composition and promoted the formation of iron plaque on the root surface, only caffeic acid, possessing a similar structure to the intermediate metabolite of PHE (catechol), could accelerate the PHE degradation rate. Caffeic acid, notable for its catechol structure, plays a significant role in enhancing PHE degradation through two main mechanisms: (a) it directly boosts PHE co-metabolism by fostering the growth of PHE-degrading bacteria, specifically Burkholderiaceae, and by facilitating the production of the key metabolic enzyme catechol 1,2-dioxygenase (C12O) and (b) it indirectly supports PHE biodegradation by promoting iron plaque formation on root surfaces, thereby enriching free iron for efficient microbial synthesis of C12O, a crucial factor in PHE decomposition.

Photodegradation of polycyclic aromatic hydrocarbons on soil surface: Kinetics and quantitative structure-activity relationship (QSAR) model development

Polycyclic aromatic hydrocarbons (PAHs) have attracted much attention because of their widespread existence and toxicity. Photodegradation is the main natural decay process of PAHs in soil. The photodegradation kinetics of benzopyrene (BaP) on 16 kinds of soils and 10 kinds of PAHs on Hebei (HE) soil were studied. The results showed that BaP had the highest degradation rate in Shaanxi (SN) soil (kobs = 0.11 min-1), and anthracene (Ant) was almost completely degraded after 16 h of irradiation in HE soil. Two quantitative structure-activity relationship (QSAR) models were established by the multiple linear regression (MLR) method. The developed QSAR models have good stability, robustness and predictability. The model revealed that the main factors affecting the photodegradation of PAHs are soil organic matter (SOM) and the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (Egap). SOM can function as a photosensitizer to induce the production of active species for photodegradation, thus favoring the photodegradation of PAHs. In addition, compounds with lower Egap are less stable and more reactive, and thus are more prone to photodegradation. Finally, the QSAR model was optimized using machine learning approach. The results of this study provide basic information on the photodegradation of PAHs and have important significance for predicting the environmental behavior of PAHs in soil.

Performance enhancement of white rot fungi extracellular enzymes via new hydrogel microenvironments for remediation of benzo[a]pyrene contaminated soil

Organic pollutants with low solubility and high ecotoxicity, mutagenicity, and carcinogenicity, are rapidly entering and accumulating in soil, resulting in soil pollution. Several methods have been investigated for remediation of organic contaminated soil, including enzymatic remediation approach. However, free enzymes are easily deactivated, which hinders their practical application in soil remediation. Immobilization of enzyme improves its stability and catalytic performance, but the immobilized material itself becomes secondary pollutants in soil. In this study, Trametes versicolor extracellular enzyme was immobilized on the degradable calcium alginate hydrogel microspheres. The laccase maintained a high activity. In addition, the addition of cellulose improved the strength of the carrier. Hydrogel microspheres solved the problems of easy inactivation of free enzyme and secondary contamination of immobilized materials. By a novel combination of extracellular enzymes and hydrogel microenvironments, immobilized enzymes not only demonstrate outstanding performance in thermal stability and pH adaptability, but also achieves a significant improvement in biocatalytic activity for benzo[a]pyrene contaminated soil. The thermal stability of immobilized enzyme was much higher than that of free enzyme. When the temperature increased to 50 °C, the activity of immobilized enzyme remained at 93.15% of the maximum enzyme activity, while the activity of free enzyme decreased to 63.76%. At pH 8, the immobilized enzyme activity maintained 74.84% of the maximum enzyme activity, while the free enzyme activity was only 11.86%. Immobilized enzymes can effectively remove 91.40% of benzo[a]pyrene from soil within 96 h. Furthermore, the catalytic oxidation of benzo[a]pyrene by enzymes that have been immobilized ultimately results in the production of 6,12-benzo[a]pyrene-dione. Molecular dynamics simulation showed that the catalytic degradation of benzo[a]pyrene was mainly through the interaction of amino acid residues PRO-391 with the Pi-alkyl of benzo[a]pyrene. This study presents an innovative strategy for designing and developing immobilized enzymes for use in biocatalytic applications related to eco-remediation of soil.

PUF-Immobilized Bjerkandera adusta DSM 3375 as a Tool for Bioremediation of Creosote Oil Contaminated Soil

Creosote oil, a byproduct of coal distillation, is primarily composed of aromatic compounds that are difficult to degrade, such as polycyclic aromatic hydrocarbons, phenolic compounds, and N-, S-, and O-heterocyclic compounds. Despite its toxicity and carcinogenicity, it is still often used to impregnate wood, which has a particularly negative impact on the condition of the soil in plants that impregnate wooden materials. Therefore, a rapid, effective, and eco-friendly technique for eliminating the creosote in this soil must be developed. The research focused on obtaining a preparation of Bjerkandera adusta DSM 3375 mycelium immobilized in polyurethane foam (PUF). It contained mold cells in the amount of 1.10 ± 0.09 g (DW)/g of the carrier. The obtained enzyme preparation was used in the bioremediation of soil contaminated with creosote (2% w/w). The results showed that applying the PUF-immobilized mycelium of B. adusta DSM 3375 over 5, 10, and 15 weeks of bioremediation, respectively, removed 19, 30, and 35% of creosote from the soil. After 15 weeks, a 73, 79, and 72% level of degradation of fluoranthene, pyrene, and fluorene, respectively, had occurred. The immobilized cells have the potential for large-scale study, since they can degrade creosote oil in soil.

Comparative study on inhibitory effects of ferulic acid and p-coumaric acid on Salmonella Enteritidis biofilm formation

Biofilm cells exhibit higher resistance than their planktonic counterparts to commonly used disinfectants in food industry. Phenolic acids are promising substitute offering less selective pressure than traditional antibiotics. This study aims to evaluate the inhibitory effects of ferulic acid (FA) and p-coumaric acid (p-CA) on Salmonella Enteritidis biofilm formation and explore the underlying inhibitory mechanisms. The minimal inhibitory concentration (MIC) of FA and p-CA were 1.0 and 0.5 mg/ml, respectively. The sub-inhibitory concentration (1/8 MIC) significantly decreased biofilm formation without growth inhibitory effects. The biomass and extracellular polymeric substances (EPS) of S. Enteritidis biofilm as well as the bacterial swimming and chemotaxis abilities were significantly decreased when exposed to sub-MIC concentrations of FA and p-CA. These two phenolic acids showed high affinity to proteins involved in flagella motility and repressed the S. Enteritidis biofilm formation-related gene expressions. Furthermore, these two phenolic acids maintained high antibiofilm efficiency in simulated food processing conditions. This study provided valuable information of multiple phenotypic and molecular responses of S. Enteritidis to these two phenolic acids.

Laccases—Versatile Enzymes Used to Reduce Environmental Pollution

The accumulation of waste and toxic compounds has become increasingly harmful to the environment and human health. In this context, the use of laccases has become a focus of interest, due to the properties of these versatile enzymes: low substrate specificity, and water formation as a non-toxic end product. Thus, we begin our study with a general overview of the importance of laccase for the environment and industry, starting with the sources of laccases (plant, bacterial and fungal laccases), the structure and mechanism of laccases, microbial biosynthesis, and the immobilization of laccases. Then, we continue with an overview of agro-waste treatment by laccases wherein we observe the importance of laccases for the biodisponibilization of substrates and the biodegradation of agro-industrial byproducts; we then show some aspects regarding the degradation of xenobiotic compounds, dyes, and pharmaceutical products. The objective of this research is to emphasize and fully investigate the effects of laccase action on the decomposition of lignocellulosic materials and on the removal of harmful compounds from soil and water, in order to provide a sustainable solution to reducing environmental pollution.

Combined bioaugmentation and biostimulation techniques in bioremediation of pentachlorophenol contaminated forest soil

Pentachlorophenol (PCP) is quite persistent in the environment and severely affects different ecosystems including forest soil. The main objective of this work was to study different bioremediation processes of artificially PCP (100 mg kg^-1) contaminated forest soil (Sc). In fact, we used bioaugmentation by adding two different bacterial consortia B1 and B2, biostimulation procedures by amendments based on forest compost (FC), municipal solid waste compost (MC), sewage sludge (SS), and phosphate, and their combined treatments. Soil physical and chemical properties, residual PCP, soil microbial biomass carbon, soil respiration and some enzymatic activities at zero time and after 30 d of incubation, were evaluated. A net reduction of PCP, 71% of the initial concentration, after 30 d-incubation occurred in the sample Sc+B1+FC, as the best performance among all treatments, due to natural attenuation, immobilization of PCP molecules in the forest soil through organic amendments, and the action of the exogenous microbial consortium B1. The single application of FC or B1 led to a depletion of PCP concentration of 52% and 41%, respectively. Soil microbial biomass carbon decreased in PCP contaminated soil but it increased when organic amendment also in combination with microbial consortia was carried out as bioremediation action. Soil respiration underwent no changes in contaminated soil and increased under FC based bioremediation treatment. These results demonstrate that the combined treatments of biostimulation and bioaugmentation might be a promising process for remediation of PCP contaminated soil.

The production of laccases by white-rot fungi under solid-state fermentation conditions

Laccases (E.C. 1.10.3.2) produced by white-rot fungi (WRF) can be widely used, but the high cost prevents their use in large-scale industrial processes. Finding a solution to the problem could involve laccase production by solid-state fermentation (SSF) simulating the natural growth conditions for WRF. SSF offers several advantages over conventional submerged fermentation (SmF), such as higher efficiency and productivity of the process and pollution reduction. The aim of this review is therefore to provide an overview of the current state of knowledge about the laccase production by WRF under SSF conditions. The focus is on variations in the up-stream process, fermentation and down-stream process and their impact on laccase activity. The variations of up-stream processing involve inoculum preparation, inoculation of the medium and formulation of the propagation and production media. According to the studies, the production process can be shortened to 5-7 days by the selection of a suitable combination of lignocellulosic material and laccase producer without the need for any additional components of the culture medium. Efficient laccase production was achieved by valorisation of wastes as agro-food, municipal wastes or waste generated from wood processing industries. This leads to a reduction of costs and an increase in competitiveness compared to other commonly used methods and/or procedures. There will be significant challenges and opportunities in the future, where SSF could become more efficient and bring the enzyme production to a higher level, especially in new biorefineries, bioreactors and biomolecular/genetic engineering.