Oxidation of polycyclic aromatic hydrocarbons using Bacillus subtilis CotA with high laccase activity and copper independence

New insights into autochthonous fungal bioaugmentation mechanisms for recalcitrant petroleum hydrocarbon components using stable isotope probing

Autochthonous fungal bioaugmentation (AFB) is a promising strategy for the microbial remediation of petroleum hydrocarbon (PH)-contaminated soils. However, the mechanisms underlying AFB, particularly for degrading recalcitrant PH components, are not fully understood. This study employed stable isotope probing (SIP) and high-throughput sequencing to investigate the AFB mechanisms of two hydrocarbon-degrading fungi, Fusarium solani LJD-11 and Aspergillus fumigatus LJD-29, focusing on three challenging PH components: n-Hexadecane (n-Hex), Benzo[a]pyrene (BaP), and Dibenzothiophene (DBT). Our findings indicate that both fungal strains significantly enhanced pollutant removal rates, with combined application yielding optimal results. AFB treatment reduced the microbial diversity index and altered the soil microbial community, especially affecting fungal populations. A significant correlation between the microbial diversity index and degradation efficiency suggests that greater diversity enhances pollutant removal. SIP analysis showed that LJD-11 and LJD-29 could directly assimilate n-Hex and DBT, but not BaP. Correlation analyses between functional microorganisms and other biological indicators suggest that the removal of pollutants is also attributable to indigenous functional bacteria. Additionally, non-inoculated functional fungi present in the soil play a crucial role in BaP degradation. These findings reveal distinct degradation pathways for the three pollutants. The addition of carrier substrate reduced the complexity of the network, while AFB treatment restored it. In addition, the combined fungal treatment resulted in higher network parameters, leading to a more complex and stable network structure. These results provide insights into the mechanisms of AFB for degrading recalcitrant PH components, underscoring its potential for in situ bioremediation of petroleum-contaminated soils.

Characterization and rational engineering of a novel laccase from Geobacillus thermocatenulatus M17 for improved lignin degradation activity

Lignin, with its complex, high-molecular-weight aromatic polymer structure and stable ether or ester bonds, greatly impedes the efficient degradation of lignocellulosic waste. Bacterial laccases have gained attention for their potential in lignocellulosic waste degradation due to their resilience in extreme conditions and ability to be produced in large quantities. In this study, a novel laccase from Geobacillus thermocatenulatus M17 was identified and expressed in E. coli BL21 (DE3). The enzymatic properties of this M17 laccase, including its tolerance to pH, temperature, metal ions, inhibitors, and organic solvents, were thoroughly investigated. The M17 laccase demonstrated optimal activity at pH 3-6 and at temperatures of 50-60 °C, with Co2+ enhancing its activity over Cu2+, and exhibited strong resistance to organic solvents. Further optimization through mutagenesis led to the engineered D217K variant. The efficiency of the engineered laccase was validated with alkali lignin and various sources of plant biomass. The degradation rate of D217K variant for alkali lignin increased significantly, rising from 66.33 % to 83.27 %. Additionally, for high-lignin-content biomass, the degradation rates improved as follows: wheat stover increased from 7.63 % to 10.29 %, switchgrass from 6.02 % to 7.00 %, and corn stalk from 4.51 % to 6.59 %. In conclusion, this study identified a new bacterial laccase and further enhanced its activity through rational engineering, suggesting its promising application in plant biomass degradation.

Bioremediation of PAHs-contaminated site in a full-scale biopiling system with immobilized enzymes: Removal efficiency and microbial communities

Bioremediation of PAHs-contaminated soil by immobilized enzymes is a promising technology. Nevertheless, the practical implementation of highly efficient enzymatic remediation remains confined to laboratory settings, with limited experience in full-scale applications. In this study, the extracellular enzymes from white rot fungi are fully applied to treat sites contaminated with PAHs by combining a new hydrogel microenvironment and a biopiling system. The full-scale project was conducted on silty loam soil contaminated with PAHs. In line with China's guidelines for construction land, 7 out of the 12 PAHs identified are considered to be a threat to the soil quality of construction sites, with benzo[a]pyrene levels reaching 1.50 mg kg-1, surpassing the acceptable limit of 0.55 mg kg-1 for the first type of land. After 7 days of remediation, the benzo[a]pyrene level decreased from 1.50 mg kg-1 to 0.51 mg kg-1, reaching the remediation standard of Class I screening values, with a removal rate of 66%. Microbiomes were utilized to assess the microbial biodiversity and structure analyses for PAHs biodegradation. The remediation enhanced the abundance of dominant bacterium (Marinobacter, Pseudomonas, and Truepera) and fugin (Thielavia, Neocosmospora, and Scedosporium). The research offers further insights into the exploration of soil remediation on the full-scale of the immobilized enzyme and biopiling technology.

Defense systems of soil microorganisms in response to compound contamination by arsenic and polycyclic aromatic hydrocarbons

Arsenic and PAHs impose environmental stress on soil microorganisms, yet their compound effects remain poorly understood. While soil microorganisms possess the ability to metabolize As and PAHs, the mechanisms of microbial response are not fully elucidated. In our study, we established two simulated soil systems using soil collected from Xixi Wetland Park grassland, Hangzhou, China. The As-600 Group was contaminated with 600 mg/kg sodium arsenite, while the As-600-PAHs-30 Group received both 600 mg/kg sodium arsenite and 30 mg/kg PAHs (phenanthrene:fluoranthene:benzo[a]pyrene = 1:1:1). These systems were operated continuously for 270 days, and microbial responses were assessed using high-throughput sequencing and metagenomic analysis. Our findings revealed that compound contamination significantly promoted the abundance of microbial defense-related genes, with general defense genes increasing by 11.07 % ∼ 74.23 % and specific defense genes increasing by 44.13 % ∼ 55.74 %. The dominate species Rhodococcus adopts these general and specific defense mechanisms to resist compound pollution stress and gain ecological niche advantages, making it a candidate strain for soil remediation. Our study contributes to the assessment of ecological damage caused by As and PAHs from a microbial perspective and provides valuable insights for soil remediation.

Applying kitchen compost promoted soil chrysene degradation by optimizing microbial community structure

Chrysene, as a high molecular weight polycyclic aromatic hydrocarbon (PAH), has become an important factor in degrading soil quality and constraining the safe production of food crops. Compost has been widely used to amend contaminated soil. However, to date, the main components of kitchen compost that enhance the biodegradation of chrysene in the soil remain unidentified. Thus, in this study, the enhancing effect and mechanisms of kitchen compost (KC) and kitchen compost-derived dissolved organic matter (KCOM) on chrysene removal from soil were investigated through cultivation experiments combined with high-throughput sequencing technology. Additionally, the key components influencing the degradation of chrysene were identified. The results showed that KCOM was the main component of compost that promoted the degradation of chrysene. The average degradation rate of chrysene in 1% KC- and 1% KCOM-treated soil increased by 27.20% and 24.18%, respectively, at different levels of chrysene pollution compared with the control treatment (CK). KC and KCOM significantly increased soil nutrient content, accelerated humification of organic matter, and increased microbial activity in the chrysene-contaminated soil. Correlation analyses revealed that the application of KC and KCOM optimized the microbial community by altering soil properties and organic matter structure. This optimization enhanced the degradation of soil chrysene by increasing the abundance of chrysene-degrading functional bacteria from the genera Bacillus, Arthrobacter, Pseudomonas, Lysinibacillus, and Acinetobacter. This study provides insight into the identification of key components that promote chrysene degradation and into the microbial-enhanced remediation of chrysene-contaminated soil.

Mechanism of non-phenolic substrate oxidation by the fungal laccase Type 1 copper site from Trametes versicolor: the case of benzo[a]pyrene and anthracene

Laccases (EC 1.10.3.2) are multicopper oxidases with the capability to oxidize diverse phenolic and non-phenolic substrates. While the molecular mechanism of their activity towards phenolic substrates is well-established, their reactivity towards non-phenolic substrates, such as polycyclic aromatic hydrocarbons (PAHs), remains unclear. To elucidate the oxidation mechanism of PAHs, particularly the activation mechanism of the sp2 aromatic C-H bond, we conducted a density functional theory investigation on the oxidation of two PAHs (anthracene and benzo[a]pyrene) using an extensive model of the T1 copper catalytic site of the fungal laccase from Trametes versicolor.

Simultaneous removal of phenanthrene and Pb using novel PPG-CNTs-nZVI beads

PPG-CNTs-nZVI bead was synthesized by polyvinyl alcohol, pumice, carbon nanotube, and guar gum-nanoscale zero-valent iron to be applied on simultaneously removal of polycyclic aromatic hydrocarbons (PAHs; phenanthrene) and heavy metals (Pb2+) via adsorption. The individual and simultaneous removal efficiency of phenanthrene and Pb2+ using the PPG-CNTs-nZVI beads was evaluated with a range of initial concentrations of these two pollutants. The kinetics and isotherms of phenanthrene and Pb2+ adsorption by the PPG-CNTs-nZVI beads were also determined. The PPG-CNTs-nZVI beads show reasonably high phenanthrene adsorption capacities (up to 0.16 mg/g), and they absorbed 85% of the phenanthrene (initial concentration 0.5 mg/L) in 30 min. High Pb2+ adsorption capabilities were also demonstrated by the PPG-CNTs-nZVI beads (up to 11.6 mg/g). The adsorption fits the Langmuir model better than the Freundlich model. The adsorption still remained stable with various ionic strength circumstances and a wide pH range (2-5). Additionally, the co-adsorption of phenanthrene and Pb2+ by the PPG-CNTs-nZVI beads resulted in synergistic effects. Particularly, phenanthrene-Pb2+ complex formation via π-cation interactions demonstrated a greater affinity than phenanthrene or Pb2+ alone. The present findings suggest that PPG-CNTs-nZVI beads may be effective sorbents for the simultaneous removal of PAHs and heavy metals from contaminated waters.

Impact of artisanal refining activities on bacterial diversity in a Niger Delta fallow land

Hydrocarbon pollution is a major ecological problem facing oil-producing countries, especially in the Niger Delta region of Nigeria. In this study, a site that had been previously polluted by artisanal refining activity was investigated using 16S rRNA Illumina high-throughput sequencing technology and bioinformatics tools. These were used to investigate the bacterial diversity in soil with varying degrees of contamination, determined with a gas chromatography-flame ionization detector (GC-FID). Soil samples were collected from a heavily polluted (HP), mildly polluted (MP), and unpolluted (control sample, CS) portion of the study site. DNA was extracted using the Zymo Research (ZR) Fungi/Bacteria DNA MiniPrep kit, followed by PCR amplification and agarose gel electrophoresis. The microbiome was characterized based on the V3 and V4 hypervariable regions of the 16S rRNA gene. QIIME (Quantitative Insights Into Microbial Ecology) 2 software was used to analyse the sequence data. The final data set covered 20,640 demultiplexed high-quality reads and a total of 160 filtered bacterial OTUs. Proteobacteria dominated samples HP and CS, while Actinobacteria dominated sample MP. Denitratisoma, Pseudorhodoplanes, and Spirilospora were the leading genera in samples HP, CS, and MP respectively. Diversity analysis indicated that CS [with 25.98 ppm of total petroleum hydrocarbon (TPH)] is more diverse than HP (with 490,630 ppm of TPH) and MP (with 5398 ppm of TPH). A functional prediction study revealed that six functional modules dominated the dataset, with metabolism covering up to 70%, and 11 metabolic pathways. This study demonstrates that a higher hydrocarbon concentration in soil adversely impacts microbial diversity, creating a narrow bacterial diversity dominated by hydrocarbon-degrading species, in addition to the obvious land and ecosystem degradation caused by artisanal refining activities. Overall, the artisanal refining business is significantly driving ecosystem services losses in the Niger Delta, which calls for urgent intervention, with focus on bioremediation.

The Effects and Toxicity of Different Pyrene Concentrations on Escherichia coli Using Transcriptomic Analysis

Pyrene is a pollutant in the environment and affects the health of living organisms. It is important to understand microbial-mediated pyrene resistance and the related molecular mechanisms due to its toxicity and biodegradability. Due to the unclear response mechanisms of bacteria to PAHs, this study detected the transcriptional changes in Escherichia coli under different pyrene concentrations using transcriptome sequencing technology. Global transcriptome analysis showed that the number of differentially expressed genes (DEGs) in multiple metabolic pathways increased with increasing concentrations of pyrene. In addition, the effects and toxicity of pyrene on Escherichia coli mainly included the up-regulation and inhibition of genes related to carbohydrate metabolism, membrane transport, sulfate reduction, various oxidoreductases, and multidrug efflux pumps. Moreover, we also constructed an association network between significantly differentially expressed sRNAs and key genes and determined the regulatory relationship and key genes of Escherichia coli under pyrene stress. Our study utilized pyrene as an exogenous stress substance to investigate the possible pathways of the bacterial stress response. In addition, this study provides a reference for other related research and serves as a foundation for future research.

Characteristic microbiome and synergistic mechanism by engineering agent MAB-1 to evaluate oil-contaminated soil biodegradation in different layer soil

Bioremediation is a sustainable and pollution-free technology for crude oil-contaminated soil. However, most studies are limited to the remediation of shallow crude oil-contaminated soil, while ignoring the deeper soil. Here, a high-efficiency composite microbial agent MAB-1 was provided containing Bacillus (naphthalene and pyrene), Acinetobacter (cyclohexane), and Microbacterium (xylene) to be synergism degradation of crude oil components combined with other treatments. According to the crude oil degradation rate, the up-layer (63.64%), middle-layer (50.84%), and underlying-layer (54.21%) crude oil-contaminated soil are suitable for bioaugmentation (BA), biostimulation (BS), and biostimulation+bioventing (BS+BV), respectively. Combined with GC-MS and carbon number distribution analysis, under the optimal biotreatment, the degradation rates of 2-ring and 3-ring PAHs in layers soil were about 70% and 45%, respectively, and the medium and long-chain alkanes were reduced during the remediation. More importantly, the relative abundance of bacteria associated with crude oil degradation increased in each layer after the optimal treatment, such as Microbacterium (2.10-14%), Bacillus (2.56-12.1%), and Acinetobacter (0.95-12.15%) in the up-layer soil; Rhodococcus (1.5-6.9%) in the middle-layer soil; and Pseudomonas (3-5.4%) and Rhodococcus (1.3-13.2%) in the underlying-layer soil. Our evaluation results demonstrated that crude oil removal can be accelerated by adopting appropriate bioremediation approach for different depths of soil, providing a new perspective for the remediation of actual crude oil-contaminated sites.

Aerobic Microbial Transformation of Fluorinated Liquid Crystal Monomer: New Pathways and Mechanism

Fluorinated liquid crystal monomers (FLCMs) have been suggested as emerging contaminants, raising global concern due to their frequent occurrence, potential toxic effects, and endurance capacity in the environment. However, the environmental fate of the FLCMs remains unknown. To fill this knowledge gap, we investigated the aerobic microbial transformation mechanisms of an important FLCM, 4-[difluoro(3,4,5-trifluorophenoxy)methyl]-3, 5-difluoro-4'-propylbiphenyl (DTMDPB), using an enrichment culture termed as BG1. Our findings revealed that 67.5 ± 2.1% of the initially added DTMDPB was transformed in 10 days under optimal conditions. A total of 14 microbial transformation products obtained due to a series of reactions (e.g., reductive defluorination, ether bond cleavage, demethylation, oxidative hydroxylation and aromatic ring opening, sulfonation, glucuronidation, O-methylation, and thiolation) were identified. Consortium BG1 harbored essential genes that could transform DTMDPB, such as dehalogenation-related genes [e.g., glutathione S-transferase gene (GST), 2-haloacid dehalogenase gene (2-HAD), nrdB, nuoC, and nuoD]; hydroxylating-related genes hcaC, ubiH, and COQ7; aromatic ring opening-related genes ligB and catE; and methyltransferase genes ubiE and ubiG. Two DTMDPB-degrading strains were isolated, which are affiliated with the genus Sphingopyxis and Agromyces. This study provides a novel insight into the microbial transformation of FLCMs. The findings of this study have important implications for the development of bioremediation strategies aimed at addressing sites contaminated with FLCMs.

Production and characterization of novel thermostable CotA-laccase from Bacillus altitudinis SL7 and its application for lignin degradation

Laccases are multi-copper oxidases and found in ligninolytic bacteria catalyzing the oxidation of both phenolic and non-phenolic compounds, however its application in lignin degradation suffers due to low oxidation rate, which have intensified the search for new laccases. In the present study, spore coat A protein (CotA) encoding gene having laccase like activity from Bacillus altitudinis SL7 (CotA-SL7) was cloned and expressed in Escherichia coli. The purified CotA-SL7 was active at wide range of temperature and pH with optimum activity at 55 °C and pH 5.0. The kinetic parameters of CotA-SL7 was determined with Km, Vmax, and kcat values 0.4 mM, 2777 μmol/min/mg, and 5194 s-1, respectively. Molecular docking revealed the presence of Pro, Phe, Asp, Asn, His, and Ile residues at the active site taking part in the oxidation of ABTS. The purified CotA-SL7 reduced lignin contents by 31 % and changes in lignin structure were analyzed through fourier transformed infrared spectroscopy (FTIR), scanning electron microsscopy (SEM) and gas chromatography mass-spectrometry (GC-MS). The appearance of low molecular size compounds clearly indicates the cleavage of lignin polymer and opening of the benzene ring by purified CotA-SL7. Thus, high catalytic efficiency of CotA-SL7 makes it a suitable bio-catalyst for remediation of lignin contaminated wastewater from pulp and paper industries with clear insights into lignin degradation at molecular level.

The role of microplastics in the process of laccase-assisted phytoremediation of phenanthrene-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic organic pollutants widely distributed in terrestrial environments and laccase was considered as an effective enzyme in PAHs bioremediation. However, laccase-assisted phytoremediation of PAHs-contaminated soil has not been reported. Moreover, the overuse of plastic films in agriculture greatly increased the risk of co-existence of PAHs and microplastics in soil. Microplastics can adsorb hydrophobic organics, thus altering the bioavailability of PAHs and ultimately affecting the removal of PAHs from soil. Therefore, this study aimed to evaluate the efficiency of laccase-assisted maize (Zea mays L.) in the remediation of phenanthrene (PHE)-contaminated soil and investigate the effect of microplastics on this remediation process. The results showed that the combined application of laccase and maize achieved a removal efficiency of 83.47 % for soil PHE, and laccase significantly reduced the accumulation of PHE in maize. However, microplastics significantly inhibited the removal of soil PHE (10.88 %) and reduced the translocation factor of PHE in maize (87.72 %), in comparison with PHE + L treatment. Moreover, microplastics reduced the laccase activity and the relative abundance of some PAHs-degrading bacteria in soil. This study provided an idea for evaluating the feasibility of the laccase-assisted plants in the remediation of PAHs-contaminated soil, paving the way for reducing the risk of secondary pollution in the process of phytoremediation.

Laccase Lac-W detoxifies aflatoxin B1 and degrades five other major mycotoxins in the absence of redox mediators

A multicopper oxidase Lac-W from Weizmannia coagulans 36D1 was identified and characterized as a laccase (Lac-W) with a robust enzymatic activity, which was used in various mycotoxins degradation. We demonstrated that Lac-W could directly degrade six major mycotoxins in the absence of redox mediators in pH 9.0, 24h static incubation at room temperature, including aflatoxin B1 (AFB1, 88%), zearalenone (60%), deoxynivalenol (34%), T-2 toxin (19%), fumonisin B1 (18%), and ochratoxin A (12%). The optimal condition for Lac-W to degrade AFB1 was 30 °C, pH 9.0, enzyme-substrate ratio 3U/μg in 24h static condition. Furthermore, we characterized aflatoxin Q1 as a Lac-W-mediated degradation product of AFB1 using UHPLC-MS/MS. Interestingly, degradation products of AFB1 failed to generate cell death and apoptosis of intestinal porcine epithelial cells. Finally, our molecular docking simulation results revealed that the substrate-binding pocket of Lac-W was large enough to allow the entry of six mycotoxins with different structures, and their degradation rates were positively correlated to their interacting affinity with Lac-W. In summary, the unique properties of the Lac-W make it a great candidate for detoxifying multiple mycotoxins contaminated food and feed cost-effectively and eco-friendly. Our study provides new insights into development of versatile enzymes which could simultaneously degrade multiple mycotoxins.

Bisphenols-A Threat to the Natural Environment

Negative public sentiment built up around bisphenol A (BPA) follows growing awareness of the frequency of this chemical compound in the environment. The increase in air, water, and soil contamination by BPA has also generated the need to replace it with less toxic analogs, such as Bisphenol F (BPF) and Bisphenol S (BPS). However, due to the structural similarity of BPF and BPS to BPA, questions arise about the safety of their usage. The toxicity of BPA, BPF, and BPS towards humans and animals has been fairly well understood. The biodegradability potential of microorganisms towards each of these bisphenols is also widely recognized. However, the scale of their inhibitory pressure on soil microbiomes and soil enzyme activity has not been estimated. These parameters are extremely important in determining soil health, which in turn also influences plant growth and development. Therefore, in this manuscript, knowledge has been expanded and systematized regarding the differences in toxicity between BPA and its two analogs. In the context of the synthetic characterization of the effects of bisphenol permeation into the environment, the toxic impact of BPA, BPF, and BPS on the microbiological and biochemical parameters of soils was traced. The response of cultivated plants to their influence was also analyzed.

Shrimp laccase degrades polycyclic aromatic hydrocarbons from an oil spill disaster in Brazil: A tool for marine environmental bioremediation

Our work aims to purify, characterize and evaluate a laccase from by-products of the shrimp farming industry (Litopenaeus vannamei) for the degradation of Polycyclic Aromatic Hydrocarbons (PAHs) from 2019 oil spill in Brazilian coast. The enzyme was purified by affinity chromatography and characterized as thermostable, with activity above 90 °C and at alkaline pH. In addition, the laccase was also tolerant to copper, lead, cadmium, zinc, arsenic, hexane and methanol, with significant enzymatic activation in acetone and 10 mM mercury. Concerning PAHs' degradation, the enzyme degraded 42.40 % of the total compounds, degrading >50 % of fluorene, C4-naphthalenes, C3-naphthalenes, C2-naphthalenes, anthracene, acenaphthene, 1-methylnaphthalene and 2-methylnaphthalene. Thus, this laccase demonstrated important characteristics for bioremediation of marine environments contaminated by crude oil spills, representing a viable and ecological alternative for these purposes.

New insight into the mechanisms of autochthonous fungal bioaugmentation of phenanthrene in petroleum contaminated soil by stable isotope probing

Autochthonous fungal bioaugmentation (AFB) is considered a reliable bioremediation approach for polycyclic aromatic hydrocarbon (PAH) contamination, but little is known about its mechanisms in contaminated soils. Here, a microcosm experiment was performed to explore the AFB mechanisms associated with two highly efficient phenanthrene degrading agents of fungi (with laccase-producing Scedosporium aurantiacum GIG-3 and non-laccase-producing Aspergillus fumigatus LJD-29), using stable-isotope-probing (SIP) and high-throughput sequencing. The results showed that each fungus markedly improved phenanthrene removal, and microcosms with both fungi exhibited the best phenanthrene removal performance among all microcosms. Additionally, AFB markedly shifted the composition of the microbial community, particularly the phenanthrene-degrading bacterial taxa. Interestingly, based on SIP results, strains GIG-3 and LJD-29 did not assimilate phenanthrene directly during AFB, but instead played key roles in the preliminary decomposition of phenanthrene though secretion of different extracellular enzymes to oxidize the benzene ring (GIG-3 bioaugmentation with laccase, and LJD-29 bioaugmentation with manganese and lignin peroxidases). In addition, all functional degraders directly involved in phenanthrene assimilation were indigenous bacteria, while native fungi rarely participated in the direct phenanthrene mineralization. Our findings provide a new mechanism of AFB with multiple fungi, and support AFB as a promising strategy for the in situ bioremediation of PAH-contaminated soil.

Depolymerization of lignin using laccase from Bacillus sp. PCH94 for production of valuable chemicals: A sustainable approach for lignin valorization

Lignin is the most abundant aromatic polymer in nature, and its depolymerization offers excellent opportunities to develop renewable aromatic chemicals. In the present study, Bacillus sp. PCH94 was investigated for laccase production and lignin depolymerization. Maximum production of laccase enzyme was achieved within 6.0 h at 50 °C on a natural lignocellulosic substrate. Furthermore, Bacillus sp. PCH94 was used to bioconvert lignin dimeric and polymeric substrates, validated using FT-IR, NMR (¹H, ¹³C), and LCMS. Genome mining of Bacillus sp. PCH94 revealed laccase gene (lac^Bl) as multicopper oxidase (spore coat CotA). Further, lac^Bl from Bacillus sp. PCH94 was cloned, expressed, and kinetically characterized. Lac^Bl enzyme showed activity for substrates ABTS (40.64 IU/mg), guaiacol (5.43 IU/mg), and DMP (11.93 IU/mg). The Lac^Bl was active in higher temperatures (10 to 100 °C) and showed a half-life of 36 and 27 h at 50 and 60 °C, respectively. The purified Lac^Bl was able to depolymerize kraft lignin into valuable products (ferulic acid and acetovanillone), which have applications in the pharmaceutical and food industries. Overall, the current study demonstrated the role of bacterial laccase in the depolymerization of lignin and opened a promising prospect for the green production of valuable compounds from recalcitrant lignin.

Heterologous Expression of the Lactobacillus sakei Multiple Copper Oxidase to Degrade Histamine and Tyramine at Different Environmental Conditions

Biogenic amines (BAs) are produced by microbial decarboxylation in various foods. Histamine and tyramine are recognized as the most toxic of all BAs. Applying degrading amine enzymes such as multicopper oxidase (MCO) is considered an effective method to reduce BAs in food systems. This study analyzed the characterization of heterologously expressed MCO from L. sakei LS. Towards the typical substrate 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), the optimal temperature and pH for recombinant MCO (rMCO) were 25 °C and 3.0, respectively, with the specific enzyme activity of 1.27 U/mg. Then, the effect of different environmental factors on the degrading activity of MCO towards two kinds of BAs was investigated. The degradation activity of rMCO is independent of exogenous copper and mediators. Additionally, the oxidation ability of rMCO was improved for histamine and tyramine with an increased NaCl concentration. Several food matrices could influence the amine-oxidizing activity of rMCO. Although the histamine-degrading activities of rMCO were affected, this enzyme reached a degradation rate of 28.1% in the presence of surimi. Grape juice improved the tyramine degradation activity of rMCO by up to 31.18%. These characteristics of rMCO indicate that this enzyme would be a good candidate for degrading toxic biogenic amines in food systems.

Catalyzed degradation of polycyclic aromatic hydrocarbons by recoverable magnetic chitosan immobilized laccase from Trametes versicolor

The capability of laccase to oxidate a broad range of polyphenols and aromatic substrates in vitro offers a new technological option for the remediation of polycyclic aromatic hydrocarbon (PAH) pollution with high cytotoxicity. However, laccase application in the remediation of PAH-contaminated sites mainly suffers from a low oxidation rate and high cost because of the difficulty in its recovery. In this study, laccases were immobilized on magnetic Fe₃O₄ particles coated with chitosan (Fe₃O₄@SiO₂-chitosan) to improve the operational stability and reusability in the treatment of PAH pollution. The enzyme fixation capacity reached 158 mg g^-1, and 79.1% of free laccase activities were reserved under the optimum immobilized condition of 4% glutaraldehyde, 1.0 mg mL^-1 laccase, 2 h covalent bonding time, and 6 h fixation time. The degradation efficiencies of anthracene (ANT) and benzo[a]pyrene (B(a)P) by Fe₃O₄@SiO₂-chitosan immobilized laccase in 48 h were 81.9% and 69.2%, respectively. Furthermore, it is very easy to magnetically recover the immobilized laccase from reaction systems and reuse it in a new batch. The relative activities of immobilized laccase were over 50% for the degradation of ANT and B(a)P in three catalytic runs, reaching the goal of substantially reducing cost in practice. According to the results from quantum calculations and mass spectrum analyses, the degradation products of ANT and B(a)P by laccase were anthraquinone and B(a)P-dione, respectively. The findings from this study provide valuable insight in promoting the application of immobilized laccase technology in the remediation of PAH contamination.

Improving Degradation of Polycyclic Aromatic Hydrocarbons by Bacillus atrophaeus Laccase Fused with Vitreoscilla Hemoglobin and a Novel Strong Promoter Replacement

Laccases catalyze a variety of electron-rich substrates by reducing O2 to H2O, with O2 playing a vital role as the final electron acceptor in the reaction process. In the present study, a laccase gene, lach5, was identified from Bacillus atrophaeus through sequence-based screening. LacH5 was engineered for modification by fusion expression and promoter replacement. Results showed that the purified enzyme LacH5 exhibited strong oxidative activity towards 2,2'-azinobis(3-ehtylbenzothiazolin-6-sulfnic acid) ammonium salt (ABTS) under optimum pH and temperature conditions (pH 5.0, 60 °C) and displayed remarkable thermostability. The activity of the two fusion enzymes was enhanced significantly from 14.2 U/mg (LacH5) to 22.5 U/mg (LacH5-vgb) and 18.6 U/mg (Vgb-lacH5) toward ABTS after LacH5 fusing with Vitreoscilla hemoglobin (VHb). Three of six tested polycyclic aromatic hydrocarbons (PAHs) were significantly oxidized by two fusion laccases as compared with LacH5. More importantly, the expression level of LacH5 and fusion protein LacH5-vgb was augmented by 3.7-fold and 7.0-fold, respectively, by using a novel strong promoter replacement. The results from the current investigation provide new insights and strategies for improving the activity and expression level of bacterial laccases, and these strategies can be extended to other laccases and multicopper oxidases.

Biodegradation of tricresyl phosphates isomers by a novel microbial consortium and the toxicity evaluation of its major products

A novel microbial consortium ZY1 capable of degrading tricresyl phosphates (TCPs) was isolated, it could quickly degrade 100% of 1 mg/L tri-o-cresyl phosphate (ToCP), tri-p-cresyl phosphate (TpCP) and tri-m-cresyl phosphate (TmCP) within 36, 24 and 12 h separately and intracellular enzymes occupied the dominated role in TCPs biodegradation. Additionally, triphenyl phosphate (TPHP), 2-ethylhexyl diphenyl phosphate (EHDPP), bisphenol-A bis (diphenyl phosphate) (BDP), tris (2-chloroethyl) phosphate (TCEP) and tris (1-chloro-2-propyl) phosphate (TCPP) could also be degraded by ZY1 and the aryl-phosphates was easier to be degraded. The TCPs reduction observed in freshwater and seawater indicated that high salinity might weak the degradability of ZY1. The detected degradation products suggested that TCPs was mainly metabolized though the hydrolysis and hydroxylation. Sequencing analysis presented that the degradation of TCPs relied on the cooperation between sphingobacterium, variovorax and flavobacterium. The cytochrome P450/NADPH-cytochrome P450 reductase and phosphatase were speculated might involve in TCPs degradation. Finally, toxicity evaluation study found that the toxicity of the diesters products was lower than their parent compound based on the generation of the intracellular reactive oxygen (ROS) and the apoptosis rate of A549 cell. Taken together, this research provided a new insight for the bioremediation of TCPs in actual environment.

Investigating the effect of nanoparticle on phenanthrene biodegradation by Labedella gwakjiensis strain KDI

Polycyclic aromatic hydrocarbons (PAHs), as persistent organic contaminants, are a major source of concern due to their toxic effect on ecosystems and human health. This study attempted to isolate halotolerant PAHs degrading bacteria from saline oil-contaminated soils. Among the isolates, strain KDI with the highest 16S rRNA gene sequence similarity to Labedella gwakjiensis was able to reduce surface tension (ST) from 65.42 to 26.60 mN m^-1 and increase the emulsification index to 81.04%, as a result of significant biosurfactant production. Response Surface Methodology (RSM) analysis was applied to optimize the factors, i.e. PAHs concentration and NaCl concentration as well as to determine the effect of these important variables on PAHs biodegradation. The Carbon Quantum Dots. Iron Oxide (CQDs.Fe₃O₄) nanoparticles were characterized by several popular analytical techniques, after which the effect of CQD.Fe₃O₄ nanoparticles on biodegradation was examined. PAHs biodegradation rate and efficiency of strain KDI to degrade PHE in the presence of CQD.Fe₃O₄ nanoparticles was analyzed by GC. According to the results during biodegradation both the concentration of PAHs and the amount of NaCl were effective. The biodegradation rate significantly increased in the presence of CQD.Fe₃O₄. The highest biodegradation of PHE occurred in the presence of 0.5 g/L of CQD.Fe₃O₄ which was 63.63% and 81.77% after 48 and 72 h of incubation. To the best of our knowledge, this is the first report on optimization of PAHs concentration and salinity by RSM and nanobioremediation of PHE using a bacterial strain in the presence of CQD.Fe₃O₄ nanoparticles.

Assessment of Physicochemical, Microbiological and Toxicological Hazards at an Illegal Landfill in Central Poland

This study aimed to assess the physicochemical, microbiological and toxicological hazards at an illegal landfill in central Poland. The research included the analysis of airborne dust (laser photometer), the number of microorganisms in the air, soil and leachate (culture method) and the microbial diversity in the landfill environment (high-throughput sequencing on the Illumina Miseq); the cytotoxicity (PrestoBlue) and genotoxicity (alkaline comet assay) of soil and leachate were tested. Moreover, an analysis of UHPLC-Q-ToF-UHRMS (ultra-high-performance liquid chromatography-quadrupole-time-of-flight ultrahigh-resolution mass spectrometry) was performed to determine the toxic compounds and microbial metabolites. The PM₁ dust fraction constituted 99.89% and 99.99% of total dust and exceeded the threshold of 0.025 mg m⁻³ at the tested locations. In the air, the total number of bacteria was 9.33 × 10¹–1.11 × 10³ CFU m⁻³, while fungi ranged from 1.17 × 10² to 4.73 × 10² CFU m⁻³. Psychrophilic bacteria were detected in the largest number in leachates (3.3 × 10⁴ to 2.69 × 10⁶ CFU mL⁻¹) and in soil samples (8.53 × 10⁵ to 1.28 × 10⁶ CFU g⁻¹). Bacteria belonging to Proteobacteria (42–64.7%), Bacteroidetes (4.2–23.7%), Actinobacteria (3.4–19.8%) and Firmicutes (0.7–6.3%) dominated. In the case of fungi, Basidiomycota (23.3–27.7%), Ascomycota (5.6–46.3%) and Mortierellomycota (3.1%) have the highest abundance. Bacteria (Bacillus, Clostridium, Cellulosimicrobium, Escherichia, Pseudomonas) and fungi (Microascus, Chrysosporium, Candida, Malassezia, Aspergillus, Alternaria, Fusarium, Stachybotrys, Cladosporium, Didymella) that are potentially hazardous to human health were detected in samples collected from the landfill. Tested leachates and soils were characterised by varied cyto/genotoxins. Common pesticides (carbamazepine, prometryn, terbutryn, permethrin, carbanilide, pyrethrin, carbaryl and prallethrin), quaternary ammonium compounds (benzalkonium chlorides), chemicals and/or polymer degradation products (melamine, triphenylphosphate, diphenylphtalate, insect repellent diethyltoluamide, and drugs (ketoprofen)) were found in soil and leachate samples. It has been proven that the tested landfill is the source of the emission of particulate matter; microorganisms (including potential pathogens) and cyto/genotoxic compounds.

Remediation of diesel-contaminated soil by alkoxyethanol aqueous two-phase system

The increasing diesel pollution accidents pose a serious threat to the ecological environment and human health. Remediation of diesel-contaminated soil (DCS) has attracted widespread attention during the past few decades. This work proposed an approach for the remediation of DCS by alkoxyethanol aqueous two-phase extraction (ATPE), which was an application of this small molecule aqueous two-phase system (ATPS). In addition, the influence of temperature, stirring speed, stirring time, and solid-liquid ratio on the removal of diesel was explored respectively. The removal efficiency of diesel could reach more than 97.18% in 18 min. Meanwhile, ATPS had high reusability, and the removal efficiency remained above 85.17% in the reuse process. Alkoxyethanol ATPE could effectively remove diesel hydrocarbons with different carbon chain lengths and the remediation process hardly caused residual organic solvents on the soil surface according to the analysis of gas chromatography-mass spectrometry (GC-MS) and Fourier transforms infrared (FT-IR), which could be regarded as the distinct advantage compared to the traditional surfactant washing method and organic solvent extraction method. The study of soil physicochemical properties and wheat germination proved that the soil structure and properties changed little after ATPE remediation. And finally, the mechanism of alkoxyethanol ATPE was intensively discussed according to the remediation characteristic. This work provided an efficient method for the remediation of DCS and widened the application fields of alkoxyethanol ATPS as well.

Bioremediation of PAHs and heavy metals co-contaminated soils: Challenges and enhancement strategies

Systemic studies on the bioremediation of co-contaminated PAHs and heavy metals are lacking, and this paper provides an in-depth review on the topic. The released sources and transport of co-contaminated PAHs and heavy metals, including their co-occurrence through formation of cation-π interactions and their adsorption in soil are examined. Moreover, it is investigated that co-contamination of PAHs and heavy metals can drive a synergistic positive influence on bioremediation through enhanced secretion of extracellular polymeric substances (EPSs), production of biosynthetic genes, organic acid and enzymatic proliferation. However, PAHs molecular structure, PAHs-heavy metals bioavailability and their interactive cytotoxic effects on microorganisms can exert a challenging influence on the bioremediation under co-contaminated conditions. The fluctuations in bioavailability for microorganisms are associated with soil properties, chemical coordinative interactions, and biological activities under the co-contaminated PAHs-heavy metals conditions. The interactive cytotoxicity caused by the emergence of co-contaminants includes microbial cell disruption, denaturation of DNA and protein structure, and deregulation of antioxidant biological molecules. Finally, this paper presents the emerging strategies to overcome the bioavailability problems and recommends the use of biostimulation and bioaugmentation along with the microbial immobilization for enhanced bioremediation of PAHs-heavy metals co-contaminated sites. Better knowledge of the bioremediation potential is imperative to improve the use of these approaches for the sustainable and cost-effective remediation of PAHs and heavy metals co-contamination in the near future.

Bisphenol A-A Dangerous Pollutant Distorting the Biological Properties of Soil

Bisphenol A (BPA), with its wide array of products and applications, is currently one of the most commonly produced chemicals in the world. A narrow pool of data on BPA–microorganism–plant interaction mechanisms has stimulated the following research, the aim of which has been to determine the response of the soil microbiome and crop plants, as well as the activity of soil enzymes exposed to BPA pressure. A range of disturbances was assessed, based on the activity of seven soil enzymes, an abundance of five groups of microorganisms, and the structural diversity of the soil microbiome. The condition of the soil was verified by determining the values of the indices: colony development (CD), ecophysiological diversity (EP), the Shannon–Weaver index, and the Simpson index, tolerance of soil enzymes, microorganisms and plants (TI_BPA), biochemical soil fertility (BA₂₁), the ratio of the mass of aerial parts to the mass of plant roots (PR), and the leaf greenness index: Soil and Plant Analysis Development (SPAD). The data brought into sharp focus the adverse effects of BPA on the abundance and ecophysiological diversity of fungi. A change in the structural composition of bacteria was noted. Bisphenol A had a more beneficial effect on the Proteobacteria than on bacteria from the phyla Actinobacteria or Bacteroidetes. The microbiome of the soil exposed to BPA was numerously represented by bacteria from the genus Sphingomonas. In this object pool, the highest fungal OTU richness was achieved by the genus Penicillium, a representative of the phylum Ascomycota. A dose of 1000 mg BPA kg⁻¹ d.m. of soil depressed the activity of dehydrogenases, urease, acid phosphatase and β-glucosidase, while increasing that of alkaline phosphatase and arylsulfatase. Spring oilseed rape and maize responded significantly negatively to the soil contamination with BPA.

Heterologous expression of bacterial CotA-laccase, characterization and its application for biodegradation of malachite green

Malachite green (MG) is used as fungicide/parasiticide in aquaculture, its persistence is detrimental as it exhibits carcinogenic effects to aquatic organisms. Bacterial laccase evaluated as the best enzyme at extreme condition for aquatic MG removal. Study aims to increase laccase concentration, CotA-laccase from Bacillus subtilis was cloned and overexpressed in Escherichia coli. Optimal catalysis for purified CotA-laccase were at pH 5.0, 60 °C, and 1 mM of (2,2-azino-di-[3-ethylbenzothiazoline-sulphonate-(6)]) with Km and Kcat 0.087 mM and 37.64 S^-1 respectively. MG biodegradation by CotA-laccase in clam and tilapia pond wastewaters and cytotoxic effect of biodegraded products in grouper fin-1 cells were determined. MG degradation by CotA-laccase was equally efficient, exhibiting upto 90-94% decolorization at freshwater and saline conditions and treated solution was non-toxic to GF-1 cells. Thus, recombinant-CotA-laccase could be an environmentally-friendly enzyme for aquaculture to remove MG, thereby effective to reduce its accumulation in aquatic organisms and ensuring safe aquaculture products.

Novel Cold-Adapted Recombinant Laccase KbLcc1 from Kabatiella bupleuri G3 IBMiP as a Green Catalyst in Biotransformation

Cold-adapted enzymes are useful tools in the organic syntheses conducted in mixed aqueous-organic or non-aqueous solvents due to their molecular flexibility that stabilizes the proteins in low water activity environments. A novel psychrophilic laccase gene from Kabatiella bupleuri, G3 IBMiP, was spliced by Overlap-Extension PCR (OE-PCR) and expressed in Pichia pastoris. Purified recombinant KbLcc1 laccase has an optimal temperature of 30 °C and pH of 3.5, 5.5, 6.0, and 7.0 in the reaction with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), guaiacol, sinapic acid, and syringaldazine, respectively. Moreover, laccase KbLcc1 is highly thermolabile, as it loses 40% of activity after 30 min at 40 °C and is inactivated at 50 °C after the same period of incubation. The new enzyme remained active with 1 mM of Ni2+, Cu2+, Mn2+, and Zn2+ and with 2 mM of Co2+, Ca2+, and Mg2+, but Fe2+ greatly inhibited the laccase activity. Moreover, 1% ethanol had no impact on KbLcc1, although acetone and ethyl acetate decreased the laccase activity. The presence of hexane (40%, v/v) caused a 58% increase in activity. Laccase KbLcc1 could be applied in the decolorization of synthetic dyes and in the biotransformation of ferulic acid to vanillin. After 5 days of reaction at 20 °C, pH 3.5, with 1 mM ABTS as a mediator, the vanillin concentration was 21.9 mg/L and the molar yield of transformation reached 14.39%.

Pollutant Degrading Enzyme: Catalytic Mechanisms and Their Expanded Applications

The treatment of environmental pollution by microorganisms and their enzymes is an innovative and socially acceptable alternative to traditional remediation approaches. Microbial biodegradation is often characterized with high efficiency as this process is catalyzed via degrading enzymes. Various naturally isolated microorganisms were demonstrated to have considerable ability to mitigate many environmental pollutants without external intervention. However, only a small fraction of these strains are studied in detail to reveal the mechanisms at the enzyme level, which strictly limited the enhancement of the degradation efficiency. Accordingly, this review will comprehensively summarize the function of various degrading enzymes with an emphasis on catalytic mechanisms. We also inspect the expanded applications of these pollutant-degrading enzymes in industrial processes. An in-depth understanding of the catalytic mechanism of enzymes will be beneficial for exploring and exploiting more degrading enzyme resources and thus ameliorate concerns associated with the ineffective biodegradation of recalcitrant and xenobiotic contaminants with the help of gene-editing technology and synthetic biology.

Efficient decolorization of recalcitrant dyes at neutral/alkaline pH by a new bacterial laccase-mediator system

Laccases and laccase-mediator systems (LMS) are versatile catalysts that can oxidize a broad range of substrates coupled to the sole reduction of dioxygen to water. They possess many biotechnological applications in paper, textile, and food industries, bioethanol production, organic synthesis, detection and degradation of pollutants, and biofuel cell development. In particular, bacterial laccases are getting relevance due to their activity in a wide range of pH and temperature and their robustness under harsh conditions. However, the enzyme and the redox mediator's availability and costs limit their large-scale commercial use. Here we demonstrate that β-(10-phenothiazyl)-propionic acid can be used as an efficient and low-cost redox mediator for decolorizing synthetic dyes by the recombinant laccase SilA from Streptomyces ipomoeae produced in E. coli. This new LMS can decolorize more than 80% indigo carmine and malachite green in 1 h at pH = 8.0 and 2 h in tap water (pH = 6.8). Furthermore, it decolorized more than 40% of anthraquinone dye remazol brilliant blue R and 80% of azo dye xylidine ponceau in 5 h at 50 °C, pH 8.0. It supported at least 3 decolorization cycles without losing activity, representing an attractive candidate for a cost-effective and environmentally friendly LMS functional at neutral to alkaline pH.

Biodegradation of aromatic pollutants meets synthetic biology

Ubiquitously distributed microorganisms are natural decomposers of environmental pollutants. However, because of continuous generation of novel recalcitrant pollutants due to human activities, it is difficult, if not impossible, for microbes to acquire novel degradation mechanisms through natural evolution. Synthetic biology provides tools to engineer, transform or even re-synthesize an organism purposefully, accelerating transition from unable to able, inefficient to efficient degradation of given pollutants, and therefore, providing new solutions for environmental bioremediation. In this review, we described the pipeline to build chassis cells for the treatment of aromatic pollutants, and presented a proposal to design microbes with emphasis on the strategies applied to modify the target organism at different level. Finally, we discussed challenges and opportunities for future research in this field.

Removal of aspirin from aqueous solution using electroactive bacteria induced by alternating current

This study aims to improve bacterial laccase enzyme activity (LEA) and dehydrogenase activity (DHA) affecting acetylsalicylic acid (ASA) biodegradation using an alternating current (AC). A microbial consortium was inoculated in an electroactive bioreactor supplied with an AC by a function generator under operating conditions of amplitude (AMPL) = 2-10 peak-to-peak voltage (Vpp), optical fiber splice tray (OFST) = 0.1 V, and sine wave frequency = 10 Hz. The obtained results revealed that at an applied voltage of 8 Vpp and an OFST of 0.1 for 12 h, the maximum bacterial LEA and DHA were 30.6 U/mL and 75.5 micro grTF/cm2.gr biomass; respectively. Cell viability and permeability were equal to 95.7% and 0.3%; respectively, at the voltage of 8 Vpp. Moreover, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) analyses showed that by-products had lower intensity at 8 Vpp compared with that of 2 Vpp voltage. Finally, the results demonstrated an optimum applied voltage of the AC, which could stimulate and promote bacterial LEA and DHA. Therefore, an electroactive bioreactor supplied with an AC can be a novel system for stimulation of enzyme activities in the process of ASA biodegradation.

Use of Copper as a Trigger for the in Vivo Activity of E. coli Laccase CueO: A Simple Tool for Biosynthetic Purposes

Laccases are multi-copper oxidases that catalyze the oxidation of various electron-rich substrates with concomitant reduction of molecular oxygen to water. The multi-copper oxidase/laccase CueO of Escherichia coli is responsible for the oxidation of Cu+ to the less harmful Cu2+ in the periplasm. CueO has a relatively broad substrate spectrum as laccase, and its activity is enhanced by copper excess. The aim of this study was to trigger CueO activity in vivo for the use in biocatalysis. The addition of 5 mM CuSO4 was proven effective in triggering CueO activity at need with minor toxic effects on E. coli cells. Cu-treated E. coli cells were able to convert several phenolic compounds to the corresponding dimers. Finally, the endogenous CueO activity was applied to a four-step cascade, in which coniferyl alcohol was converted to the valuable plant lignan (-)-matairesinol.

Cu(II) nonspecifically binding chromate reductase NfoR promotes Cr(VI) reduction

Cu(II)-enhanced microbial Cr(VI) reduction is common in the environment, yet its mechanism is unknown. The specific activity of chromate reductase, NfoR, from Staphylococcus aureus sp. LZ-01 was augmented 1.5-fold by Cu(II). Isothermal titration calorimetry and spectral data show that Cu(II) binds to NfoR nonspecifically. Further, Cu(II) stimulates the nitrobenzene reduction of NfoR, indicating that Cu(II) promotes electron transfer. The crystal structure of NfoR in complex with CuSO₄ (1.46 Å) was determined. The overall structure of NfoR-Cu(II) complex is a dimer that covalently binds with FMN and Cu(II)-binding pocket is located at the interface of the NfoR dimer. Structural superposition revealed that NfoR resembles the structure of class II chromate reductase. Site-directed mutagenesis revealed that Leu⁴⁶ and Phe¹²³ were involved in NADH binding, whereas Trp⁷⁰ and Ser⁴⁵ were the key residues for nitrobenzene binding. Furthermore, His¹⁰⁰ and Asp¹⁷¹ were preferential affinity sites for Cu(II) and that Cys¹⁶³ is an active site for FMN binding. Attenuation reductase activity in C163S can be partially restored to 54% wild type by increasing Cu(II) concentration. Partial restoration indicates dual-channel electron transfer of NfoR via Cu(II) and FMN. We propose a catalytic mechanism for Cu(II)-enhanced NfoR activity in which Cu(I) is formed transiently. Together, the current results provide an insight on Cu (II)-induced enhancement and benefit of Cr(VI) bioremediation.

Intensive removal of PAHs in constructed wetland filled with copper biochar

In this study, biochar-loading copper ions (Cu-BC), a novel composite for removing phenanthrene very efficiently from water, was prepared using the impregnation method. The performance of constructed wetlands (CWs) with these modified and original biochar as substrates was analyzed. CW with Cu-BC removed a large amount of phenanthrene (94.09 ± 3.02%). According to the surface characteristics analysis, Cu-BC can promote the removal of pollutants via complex absorption, hydrophobic adsorption, increasing the Lewis Pair and electrostatic attraction. Furthermore the higher nitrate removal rate in the treated system (91.11 ± 1.17%) was observed to have higher levels of bacterial metabolic diversity and denitrifier types. The phenanthrene accumulated in plants with this treatment system was enhanced by the role of copper in photosynthesis. It is able to boost the plant extraction of organic matter.

Biochemical tests to determine the biodegradability potential of bacterial strains in PAH polluted sites

Although the use of degrading-bacteria is one of the most efficient methods for the bioremediation of polluted sites, detection, selection and proliferation of the most efficient and competing bacteria is still a challenge. The objective of this multi-stage research was to investigate the effects of the selected bacterial strains on the degradation of anthracene, florentine, naphthalene, and oil, determined by biochemical tests. In the first stage, using the following tests: (a) biosurfactant production (emulsification, oil spreading, number of drops, drop collapse, and surface tension), (b) biofilm production, (c) activity of laccase enzyme, and (d) exopolysaccaride production, the three bacterial strains with the highest degrading potential including Bacillus pumilus, B. aerophilus, and Marinobacter hydrocarbonoclasticus were chosen. In the second stage using the following tests: (a) bacterial growth, (b) laccase enzyme activity, and (c) biosurfactant production (emulsification, oil spreading, and collapse of droplet) the degrading ability of the three selected bacterial strains plus Escherichia coli were compared. Different bacterial strains were able to degrade anthracene, florentine, naphthalene, and oil by the highest rate, three days after inoculation (DAI). However, M. hydrocarbonoclasticus showed the highest rate of florentine degradation. Although with increasing pollutant concentration the degrading potential of the bacterial strains significantly decreased, M. hydrocarbonoclasticus was determined as the most efficient bacterial strain.

Bioremediation of intertidal zones polluted by heavy oil spilling using immobilized laccase-bacteria consortium

Heavy oil pollution in the intertidal zones has become a worldwide environmental problem. In this study, bioremediation on heavy oil pollutants in the intertidal zones using an immobilized laccase-bacteria consortium system was evaluated with the aid of intertidal experimental pools built in the coastal area. It is found that degradation efficiency of the immobilized laccase-bacteria consortium for heavy oil was 66.5% after 100 days remediation, with the reaction rate constant of 0.018 d^-1. Gas Chromatograph-Mass Spectrometer analysis shows that degradation efficiency of saturated hydrocarbons and aromatic hydrocarbons were 79.2% and 78.7%, which were 64.9% and 65.1% higher than control. It is further seen that degradation of long-chain n-alkanes of C26-C35 and polycyclic aromatic hydrocarbons with more than three rings were significant. Metagenomic analysis indicates that the immobilized laccase-bacterial consortium has not only increased the biodiversity of heavy oil degrading bacteria, but also accelerated the degradation of heavy oil.

An effective in-situ method for laccase immobilization: Excellent activity, effective antibiotic removal rate and low potential ecological risk for degradation products

In this study, we used a simple in-situ biomineralization method to immobilize Bacillus subtilis (B. subtilis)-derived laccase into the copper-Trimesic acid framework (Cu-BTC), and the synthesized Laccase@Cu-BTC particles were used to degrade tetracycline and ampicillin. Compared with free laccase, the Laccase@Cu-BTC showed 16.5-fold of activity recovery, higher thermo-tolerant performance, more excellent acid-proof ability and reusability. Without any mediators, Laccase@Cu-BTC displayed high degradation efficiency (nearly 100%) for tetracycline and ampicillin in some actual water. The degradation mechanism and proposed degradation pathways of tetracycline and ampicillin were discussed technically. Besides, bacteriostatic assay and survival test of Escherichia coli (E. coli) and B. subtilis confirmed the loss of antibiotic activity for tetracycline and ampicillin, as well as the low ecotoxicity of the degradation products. Our research demonstrates that Laccase@Cu-BTC has excellent performance in the effective removal of antibiotics and the detoxification of degradation products, which make it a promising candidate for environmental recovery.

Biodegradation of Total Petroleum Hydrocarbons in Soil: Isolation and Characterization of Bacterial Strains from Oil Contaminated Soil

In this study, we isolated seven strains (termed BY1–7) from polluted soil at an oil station and evaluated their abilities to degrade total petroleum hydrocarbons (TPHs). Following 16 rRNA sequence analysis, the strains were identified as belonging to the genera Bacillus, Acinetobacter, Sphingobium, Rhodococcus, and Pseudomonas, respectively. Growth characterization studies indicated that the optimal growth conditions for the majority of the strains was at 30 °C, with a pH value of approximately 7. Under these conditions, the strains showed a high TPH removal efficiency (50%) after incubation in beef extract peptone medium for seven days. Additionally, we investigated the effect of different growth media on growth impact factors that could potentially affect the strains’ biodegradation rates. Our results suggest a potential application for these strains to facilitate the biodegradation of TPH-contaminated soil.

Quantification of Naphthalene Dioxygenase (NahAC) and Catechol Dioxygenase (C23O) Catabolic Genes Produced by Phenanthrene-Degrading Pseudomonas fluorescens AH-40

Background

Petroleum polycyclic aromatic hydrocarbons (PAHs) are known to be toxic and carcinogenic for humans and their contamination of soils and water is of great environmental concern. Identification of the key microorganisms that play a role in pollutant degradation processes is relevant to the development of optimal in situ bioremediation strategies.

Objective

Detection of the ability of Pseudomonas fluorescens AH-40 to consume phenanthrene as a sole carbon source and determining the variation in the concentration of both nahAC and C23O catabolic genes during 15 days of the incubation period.

Methods

In the current study, a bacterial strain AH-40 was isolated from crude oil polluted soil by enrichment technique in mineral basal salts (MBS) medium supplemented with phenanthrene (PAH) as a sole carbon and energy source. The isolated strain was genetically identified based on 16S rDNA sequence analysis. The degradation of PAHs by this strain was confirmed by HPLC analysis. The detection and quantification of naphthalene dioxygenase (nahAc) and catechol 2,3-dioxygenase (C23O) genes, which play a critical role during the mineralization of PAHs in the liquid bacterial culture were achieved by quantitative PCR.

Results

Strain AH-40 was identified as pseudomonas fluorescens. It degraded 97% of 150 mg phenanthrene L^-1 within 15 days, which is faster than previously reported pure cultures. The copy numbers of chromosomal encoding catabolic genes nahAc and C23O increased during the process of phenanthrene degradation.

Conclusion

nahAc and C23O genes are the main marker genes for phenanthrene degradation by strain AH-40. P. fluorescence AH-40 could be recommended for bioremediation of phenanthrene contaminated site.

Biodegradation of Bisphenol A by Sphingobium sp. YC-JY1 and the Essential Role of Cytochrome P450 Monooxygenase

Bisphenol A (BPA) is a widespread pollutant threatening the ecosystem and human health. An effective BPA degrader YC-JY1 was isolated and identified as Sphingobium sp. The optimal temperature and pH for the degradation of BPA by strain YC-JY1 were 30 °C and 6.5, respectively. The biodegradation pathway was proposed based on the identification of the metabolites. The addition of cytochrome P450 (CYP) inhibitor 1-aminobenzotriazole significantly decreased the degradation of BPA by Sphingobium sp. YC-JY1. Escherichia coli BL21 (DE3) cells harboring pET28a-bisdAB achieved the ability to degrade BPA. The bisdB gene knockout strain YC-JY1ΔbisdB was unable to degrade BPA indicating that P450_bisdB was an essential initiator of BPA metabolism in strain YC-JY1. For BPA polluted soil remediation, strain YC-JY1 considerably stimulated biodegradation of BPA associated with the soil microbial community. These results point out that strain YC-JY1 is a promising microbe for BPA removal and possesses great application potential.

CotA laccase, a novel aflatoxin oxidase from Bacillus licheniformis, transforms aflatoxin B1 to aflatoxin Q1 and epi-aflatoxin Q1

In the present study, the CotA protein from Bacillus licheniformis ANSB821 was cloned and expressed in Escherichia coli. Apart from the laccase activities, we found that the recombinant CotA could effectively oxidize aflatoxin B1 in the absence of redox mediators. The Km, Kcat and Vmax values of the recombinant CotA towards aflatoxin B1 were 60.62 μM, 0.03 s-1 and 10.08 μg min-1 mg-1, respectively. CotA-mediated aflatoxin B1 degradation products were purified and identified to be aflatoxin Q1 and epi-aflatoxin Q1. The treatment of human liver cells L-02 with aflatoxin Q1 and epi-aflatoxin Q1 did not suppress cell viability and induce apoptosis. Molecular docking simulation revealed that hydrogen bonds and van der Waals interaction played an important role in aflatoxin B1-CotA stability. These findings in the current study are promising for a possible application of CotA as a novel aflatoxin oxidase in degrading AFB1 in food.

The heterologous expression, characterization, and application of a novel laccase from Bacillus velezensis

Laccases have a huge potential in numerous environmental and industrial applications due to the ability to oxidized a wide range of substrates. Here, a novel laccase gene from the identified Bacillus velezensis TCCC 111904 was heterologously expressed in Escherichia coli. The optimal temperature and pH for oxidation by recombinant laccase (rLac) were 80 °C and 5.5, respectively, in the case of the substrate 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and 80 °C and 7.0, respectively, in the case of 2,6-dimethoxyphenol (2,6-DMP). rLac exhibited high thermostability and pH stability over a wide range (pH 3.0, 7.0, and 9.0). Additionally, most of the metal ions did not inhibit the activity of rLac significantly. rLac showed great tolerance against high concentration of NaCl, and 50.8% of its initial activity remained in the reaction system containing 500 mM NaCl compared to the control. Moreover, rLac showed a high efficiency in decolorizing different types of dyes including azo, anthraquinonic, and triphenylmethane dyes at a high temperature (60 °C) and over an extensive pH range (pH 5.5, 7.0, and 9.0). These unique characteristics of rLac indicated that it could be a potential candidate for applications in treatment of dye effluents and other industrial processes.

Applications of Microbial Laccases: Patent Review of the Past Decade (2009–2019)

There is a high number of well characterized, commercially available laccases with different redox potentials and low substrate specificity, which in turn makes them attractive for a vast array of biotechnological applications. Laccases operate as batteries, storing electrons from individual substrate oxidation reactions to reduce molecular oxygen, releasing water as the only by-product. Due to society’s increasing environmental awareness and the global intensification of bio-based economies, the biotechnological industry is also expanding. Enzymes such as laccases are seen as a better alternative for use in the wood, paper, textile, and food industries, and they are being applied as biocatalysts, biosensors, and biofuel cells. Almost 140 years from the first description of laccase, industrial implementations of these enzymes still remain scarce in comparison to their potential, which is mostly due to high production costs and the limited control of the enzymatic reaction side product(s). This review summarizes the laccase applications in the last decade, focusing on the published patents during this period.

Biochemical activity of soil contaminated with BPS, bioaugmented with a mould fungi consortium and a bacteria consortium

This study analysed the scale of bisphenol S (BPS) toxicity to the soil biochemical activity and is part of a wider effort to find solutions to restore the global soil environment balance, including elimination of the effects of ecosystem pollution with BPA, of which BPS is a significant analogue. However, since there has been no research on the effect of BPS on soil health, the objective of the study was pursued based on increasing the levels of soil contamination with the bisphenol 0, 5, 50 and 500 mg BPS kg^-1 DM of soil and by observing the response of seven soil enzymes: dehydrogenases, catalase, urease, acid phosphatase, alkaline phosphatase, arylsulphatase and β-glucosidase to the growing BPS pressure. The potential negative effect of bisphenol S was offset by bioaugmentation with a bacteria consortium-Pseudomonas umsongensis, Bacillus mycoides, Bacillus weihenstephanensis and Bacillus subtilis-and a fungi consortium Mucor circinelloides, Penicillium daleae, Penicillium chrysogenum and Aspergillus niger. BPS was found to be a significant inhibitor of the soil enzymatic activity and, in consequence, its fertility. Dehydrogenases and acid phosphatase proved to be the most susceptible to BPS pressure. Bioaugmentation with a bacteria consortium offset the negative effect of 500 mg BPS kg^-1 DM of soil by inducing an increase in the activity of acid phosphatase and alkaline phosphatase, whereas the fungi consortium stimulated the activity of β-glucosidase and acid phosphatase. A spectacular dimension of bisphenol S inhibition corresponded with both the spring rape above-ground parts and root development disorders and the content of Ca and K in them. The BPS level in soil on day 5 of the experiment decreased by 61% and by another 19% on day 60.

Laccases: structure, function, and potential application in water bioremediation

The global rise in urbanization and industrial activity has led to the production and incorporation of foreign contaminant molecules into ecosystems, distorting them and impacting human and animal health. Physical, chemical, and biological strategies have been adopted to eliminate these contaminants from water bodies under anthropogenic stress. Biotechnological processes involving microorganisms and enzymes have been used for this purpose; specifically, laccases, which are broad spectrum biocatalysts, have been used to degrade several compounds, such as those that can be found in the effluents from industries and hospitals. Laccases have shown high potential in the biotransformation of diverse pollutants using crude enzyme extracts or free enzymes. However, their application in bioremediation and water treatment at a large scale is limited by the complex composition and high salt concentration and pH values of contaminated media that affect protein stability, recovery and recycling. These issues are also associated with operational problems and the necessity of large-scale production of laccase. Hence, more knowledge on the molecular characteristics of water bodies is required to identify and develop new laccases that can be used under complex conditions and to develop novel strategies and processes to achieve their efficient application in treating contaminated water. Recently, stability, efficiency, separation and reuse issues have been overcome by the immobilization of enzymes and development of novel biocatalytic materials. This review provides recent information on laccases from different sources, their structures and biochemical properties, mechanisms of action, and application in the bioremediation and biotransformation of contaminant molecules in water. Moreover, we discuss a series of improvements that have been attempted for better organic solvent tolerance, thermo-tolerance, and operational stability of laccases, as per process requirements.

Enrichment of the soil microbial community in the bioremediation of a petroleum-contaminated soil amended with rice straw or sawdust

Two common organic wastes from agriculture (rice straw) and forestry (sawdust) were applied to a petroleum-contaminated soil to estimate their effectiveness in the removal of total petroleum hydrocarbons (TPHs) and polycyclic aromatic hydrocarbons (PAHs). Rice straw was the more effective amendment than the other treatments in reducing TPH contents and addition of sawdust resulted in a significant decrease in PAH removal, particularly high-molecular-weight (5-6 ring) PAHs. Principal coordinates analysis (PCoA) indicates that rice straw treatment separated only the bacterial community but sawdust greatly affected both the soil bacterial and fungal communities. Moreover, the abundance of some petroleum degraders such as the bacteria Sphingomonas, Idiomarina and Phenylobacterium and the fungi Humicola, Wallemia and Graphium was promoted by inputs of the two agricultural and forestry wastes. These results highlight the potential of waste applications in accelerating hydrocarbon biodegradation which may be attributed to the enrichment of keystone taxa that show strong positive associations with hydrocarbon degradation.