Oxidation of polycyclic aromatic hydrocarbons by the bacterial laccase CueO from E. coli

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.

Genomic characterization and proteomic analysis of Bacillus amyloliquefaciens in response to lignin

This study examined the lignin degradation characteristics of Bacillus amyloliquefaciens MN-13. Specifically, whole-genome sequencing and comparative proteomic analysis were performed to investigate the responses of the MN-13 strain to lignin. A maximum lignin removal of 38.0 % was achieved after 36 h of inoculation in mineral salt medium with 0.2 g/L alkaline lignin, under the following conditions: the carbon to nitrogen ratio C/N = 1/1; inoculum size 6 %; addition of glucose as an exogenous carbon source. When the MN-13 strain was inoculated into mineral salt medium with and without lignin, respectively, 831 differentially expressed proteins were identified, 404 of which were up-regulated and 427 were down-regulated. Enrichment analysis revealed that up-regulated proteins were associated with microbial metabolism in diverse environment, biosynthesis of amino acids, and pathways related to energy production, including carbon metabolism, pyruvate metabolism, the TCA cycle etc. Genomic analysis revealed that the MN-13 strain possesses many ligninolytic enzymes and aromatics degradation pathway, including benzoate degradation and aminobenzoate degradation etc. Taken together, the proteomic and genomic analyses indicated that the meta-cleavage pathway of catechol, including benzoate degradation, etc., is the main lignin degradation pathway. These findings provide new insight into lignin degradation mediated by B. amyloliquefaciens.

Three strategy rules of filamentous fungi in hydrocarbon remediation: an overview

Remediation of hydrocarbon contaminations requires much attention nowadays since it causes detrimental effects on land and even worse impacts on aquatic environments. Tools of bioremediation especially filamentous fungi permissible for cleaning up as much as conceivable, at least they turn into non-toxic residues with less consumed periods. Inorganic chemicals, CO2, H2O, and cell biomass are produced as a result of the breakdown and mineralization of petroleum hydrocarbon pollutants. This paper presents a detailed overview of three strategic rules of filamentous fungi in remediating the various aliphatic, and aromatic hydrocarbon compounds: utilizing carbons from hydrocarbons as sole energy, Co-metabolism manners (Enzymatic and Non-enzymatic theories), and Biosorption approaches. Upliftment in the degradation rate of complex hydrocarbon by the Filamentous Fungi in consortia scenario we can say, "Fungal Talk", which includes a variety of cellular mechanisms, including biosurfactant production, biomineralization, and precipitation, etc., This review not only displays its efficiency but showcases the field applications - cost-effective, reliable, eco-friendly, easy to culture as biomass, applicable in both land and any water bodies in operational environment cleanups. Nevertheless, the potentiality of fungi-human interaction has not been fully understood, henceforth further studies are highly endorsed with spore pathogenicity of the fungal species capable of high remediation rate, and the gene knockout study, if the specific peptides cause toxicity to any living matters via Genomics and Proteomics approaches, before application of any in situ or ex situ environments.

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.

A low-cost and eco-friendly recombinant protein expression system using copper-containing industrial wastewater

The development of innovative methods for highly efficient production of recombinant proteins remains a prominent focus of research in the biotechnology field, primarily due to the fact that current commercial protein expression systems rely on expensive chemical inducers, such as isopropyl β-D-thiogalactoside (IPTG). In our study, we designed a novel approach for protein expression by creating a plasmid that responds to copper. This specialized plasmid was engineered through the fusion of a copper-sensing element with an optimized multiple cloning site (MCS) sequence. This MCS sequence can be easily customized by inserting the coding sequences of target recombinant proteins. Once the plasmid was generated, it was introduced into an engineered Escherichia coli strain lacking copA and cueO. With this modified E. coli strain, we demonstrated that the presence of copper ions can efficiently trigger the induction of recombinant protein expression, resulting in the production of active proteins. Most importantly, this expression system can directly utilize copper-containing industrial wastewater as an inducer for protein expression while simultaneously removing copper from the wastewater. Thus, this study provides a low-cost and eco-friendly strategy for the large-scale recombinant protein production. To the best of our knowledge, this is the first report on the induction of recombinant proteins using industrial wastewater.

Under explored roles of microbial ligninolytic enzymes in aerobic polychlorinated biphenyl transformation

Polychlorinated biphenyls (PCBs) are persistent organic pollutants in the environment that are responsible for many adverse health effects. Bioremediation appears to be a healthy and cost-effective alternative for remediating PCB-contaminated environments. While some microbial species have been observed to be capable of transforming PCBs, only two different microbial pathways (rdh and bph pathways) have been described to be involved in PCB transformations. Ligninolytic enzymes have been observed or are under suspicion in some microbial PCB transformations. However, the role of these promising PCB-transforming enzymes, which are produced by fungi and some aerobic bacteria, is still unclear. The present review describes their role by identifying microbial PCB-transforming species and their reported ligninolytic enzymes whether proven or suspected to be involved in PCB transformations. There are several lines of evidence that ligninolytic enzymes are responsible for PCB transformations such as (1) the ability of purified laccases from Myceliophthora thermophila, Pycnoporus cinnabarinus, Trametes versicolor, Cladosporium sp, and Coprinus cumatus to transform hydroxy-PCBs; (2) the increased production of laccases and peroxidases by many fungi in the presence of PCBs; and (3) the enhanced PCB transformation by Pseudomonas stutzeri and Sinorhizobium meliloti NM after the addition of ligninolytic enzyme enhancers. However, if the involvement of ligninolytic enzymes in PCB transformation is clearly demonstrated in some fungal species, it does not seem to be implicated in all microbial species suggesting other still unknown metabolic pathways involved in PCB transformation and different from the bph and rdh pathways. Therefore, PCB transformation may involve several metabolic pathways, some involving ligninolytic enzymes, bph or rdh genes, and some still unknown, depending on the microbial species. In addition, current knowledge does not fully clarify the role of ligninolytic enzymes in PCB oxidation and dechlorination. Therefore, further studies focusing on purified ligninolytic enzymes are needed to clearly elucidate their role in PCB transformation.

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.

Microbes and microbial strategies in carcinogenic polycyclic aromatic hydrocarbons remediation: a systematic review

Degradation, detoxification, or removal of the omnipresent polycyclic aromatic hydrocarbons (PAHs) from the ecosphere as well as their prevention from entering into food chain has never appeared simple. In this context, cost-effective, eco-friendly, and sustainable solutions like microbe-mediated strategies have been adopted worldwide. With this connection, measures have been taken by multifarious modes of microbial remedial strategies, i.e., enzymatic degradation, biofilm and biosurfactant production, application of biochar-immobilized microbes, lactic acid bacteria, rhizospheric-phyllospheric-endophytic microorganisms, genetically engineered microorganisms, and bioelectrochemical techniques like microbial fuel cell. In this review, a nine-way directional approach which is based on the microbial resources reported over the last couple of decades has been described. Fungi were found to be the most dominant taxa among the CPAH-degrading microbial community constituting 52.2%, while bacteria, algae, and yeasts occupied 37.4%, 9.1%, and 1.3%, respectively. In addition to these, category-wise CPAH degrading efficiencies of each microbial taxon, consortium-based applications, CPAH degradation-related molecular tools, and factors affecting CPAH degradation are the other important aspects of this review in light of their appropriate selection and application in the PAH-contaminated environment for better human-health management in order to achieve a sustainable ecosystem.

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.

Elimination and detoxification of phenanthrene assisted by a laccase from halophile Alkalibacillus almallahensis

Phenanthrene (Phe), a tricyclic Polycyclic Aromatic Hydrocarbon (PAH), is found in high concentrations as a pollutant in various environments. In this study, the removal or (oxidizing) ability of Phe by a laccase from Alkalibacillus almallahensis was investigated. The laccase (12 U mL-1) was able to remove 63% of Phe (50 mg L-1) under optimal conditions of 40 °C, pH 8, 1.5 M NaCl and in the presence of 1 mM HBT as a laccase mediator after a 72 h incubation period. The results for the effect of different solvents, ionic and non-ionic surfactants on the activity of the halophilic laccase towards Phe showed that the addition of these compounds increase removal efficiency and complete enzymatic removal of Phe will achieve in a solution of 5% (v/v) acetone and 1.5% tween 80. The kinetic parameters K m and V max of laccase-catalyzed removal of the substrate were determined as 0.544 mM and 0.882 µmol h-1 mg-1, respectively. A microtoxicity study with respect to the inhibition of algal growth showed a decrease in toxicity of the laccase-treated Phe solution.

Comprehensive strategies of Lignocellulolytic enzyme production from microbes and their applications in various commercial-scale faculties

Activities of anthropological organisms lead to the production of massive lignocellulosic waste every year and these lignocellulolytic enzymes plays crucial role in developing eco-friendly, sustainable and economical methods for decomposing and pre-treating the biomass to produce biofuels, organic acids, feeds and enzymes. Lignocellulolytic enzymes sustainably hydrolyse the biomass and can be utilized in wide range of applications such as personal care, pharmaceutical, biofuel release, sewage treatment, food and beverage industries. Every year a significant ton of biomass waste is released and insight on these crucial enzymes could establish in all the industries. However, due to the increased demand for compost materials, biomass degradation has resulted in composting processes. Several methods for improving compost amount and quality have been explored, including increasing decomposer inoculums, stimulating microbial activity, and establishing a decomposable environment. All of these prerequisites are met by biotechnological applications. Biotechnological procedures are used to improve the activity of enzymes on biomass. It leads to an adequate supply of compost and base materials for enterprises. In terms of effectiveness and stability during the breakdown process, lignocellulolytic enzymes derived from genetically modified species outperformed naturally derived lignocellulolytic enzymes. It has the potential to increase the quality and output of by-products. This review discussed the development of lignocellulolytic enzyme families and their widespread applications in a variety of industries such as olive oil extraction, carotenoid extraction, waste management, pollution control, second-generation bio-ethanol production, textile and dyeing, pharmaceuticals, pulp and paper, animal feed, food processing industries, detergent, and agricultural industries.

Microbial Enzymes Used in Bioremediation

Emerging pollutants in nature are linked to various acute and chronic detriments in biotic components and subsequently deteriorate the ecosystem with serious hazards. Conventional methods for removing pollutants are not efficient; instead, they end up with the formation of secondary pollutants. Significant destructive impacts of pollutants are perinatal disorders, mortality, respiratory disorders, allergy, cancer, cardiovascular and mental disorders, and other harmful effects. The pollutant substrate can recognize different microbial enzymes at optimum conditions (temperature/pH/contact time/concentration) to efficiently transform them into other rather unharmful products. The most representative enzymes involved in bioremediation include cytochrome P450s, laccases, hydrolases, dehalogenases, dehydrogenases, proteases, and lipases, which have shown promising potential degradation of polymers, aromatic hydrocarbons, halogenated compounds, dyes, detergents, agrochemical compounds, etc. Such bioremediation is favored by various mechanisms such as oxidation, reduction, elimination, and ring-opening. The significant degradation of pollutants can be upgraded utilizing genetically engineered microorganisms that produce many recombinant enzymes through eco-friendly new technology. So far, few microbial enzymes have been exploited, and vast microbial diversity is still unexplored. This review would also be useful for further research to enhance the efficiency of degradation of xenobiotic pollutants, including agrochemical, microplastic, polyhalogenated compounds, and other hydrocarbons.

Improving decolorization of dyes by laccase from Bacillus licheniformis by random and site-directed mutagenesis

BACKGROUND

Dye wastewater increases cancer risk in humans. For the treatment of dyestuffs, biodegradation has the advantages of economy, high efficiency, and environmental protection compared with traditional physical and chemical methods. Laccase is the best candidate for dye degradation because of its multiple substrates and pollution-free products.

METHODS

Here, we modified the laccase gene of Bacillus licheniformis by error-prone PCR and site-directed mutagenesis and expressed in E. coli. The protein was purified by His-tagged protein purification kit. We tested the enzymatic properties of wild type and mutant laccase by single factor test, and further evaluated the decolorization ability of laccase to acid violet, alphazurine A, and methyl orange by spectrophotometry.

RESULTS

Mutant laccase Lacep69and D500G were superior to wild type laccase in enzyme activity, stability, and decolorization ability. Moreover, the laccase D500G obtained by site-directed mutagenesis had higher enzyme activity in both, and the specific activity of the purified enzyme was as high as 426.13 U/mg. Also, D500G has a higher optimum temperature of 70 °C and temperature stability, while it has a more neutral pH 4.5 and pH stability. D500G had the maximum enzyme activity at a copper ion concentration of 12 mM. The results of decolorization experiments showed that D500G had a strong overall decolorization ability, with a lower decolorization rate of 18% for methyl orange and a higher decolorization rate of 78% for acid violet.

CONCLUSION

Compared with the wild type laccase, the enzyme activity of D500G was significantly increased. At the same time, it has obvious advantages in the decolorization effect of different dyes. Also, the advantages of temperature and pH stability increase its tolerance to the environment of dye wastewater.

Bacterial Valorization of Lignin: Strains, Enzymes, Conversion Pathways, Biosensors, and Perspectives

Lignin, an aromatic polymer found in plants, has been studied for years in many biological fields. Initially, when biofuel was produced from lignocellulosic biomass, lignin was regarded as waste generated by the biorefinery and had to be removed, because of its inhibitory effects on fermentative bacteria. Although it has since proven to be a natural resource for bio-products with considerable potential, its utilization is confined by its complex structure. Hence, the microbial degradation of lignin has attracted researchers' interest to overcome this problem. From this perspective, the studies have primarily focused on fungal systems, such as extracellular peroxidase and laccase from white- and brown-rot fungi. However, recent reports have suggested that bacteria play an increasing role in breaking down lignin. This paper, therefore, reviews the role of bacteria in lignin and lignin-related research. Several reports on bacterial species in soil that can degrade lignin and their enzymes are included. In addition, a cellulolytic anaerobic bacterium capable of solubilizing lignin and carbohydrate simultaneously has recently been identified, even though the enzyme involved has not been discovered yet. The assimilation of lignin-derived small molecules and their conversion to renewable chemicals by bacteria, such as muconic acid and polyhydroxyalkanoates, including genetic modification to enhance their capability was discussed. This review also covers the indirect use of bacteria for lignin degradation, which is concerned with whole-cell biosensors designed to detect the aromatic chemicals released from lignin transformation.

Copper promotes E. coli laccase-mediated TNT biotransformation and alters the toxicity of TNT metabolites toward Tigriopus japonicus

Although laccase is involved in the biotransformation of 2,4,6-trinitrotoluene (TNT), little is known regarding the effect of E. coli laccase on TNT biotransformation. In this study, E. coli K12 served as the parental strain to construct a laccase deletion strain and two laccase-overexpressing strains. These E. coli strains were used to investigate the effect of laccase together with copper ions on the efficiency of TNT biotransformation, the variety of TNT biotransformation products generated and the toxicity of the TNT metabolites. The results showed that the laccase level was not relevant to TNT biotransformation in the soluble fraction of the culture medium. Conversely, TNT metabolites varied in the insoluble fraction analyzed by thin-layer chromatography (TLC). The insoluble fraction from the laccase-null strain showed fewer and relatively fainter spots than those detected in the wild-type and laccase-overexpressing strains, indicating that laccase expression levels were interrelated determinants of the varieties and amounts of TNT metabolites produced. In addition, the aquatic invertebrate Tigriopus japonicus was used to assess the toxicity of the TNT metabolites. The toxicity of the TNT metabolite mixture increased when the intracellular laccase level in strains increased or when purified E. coli recombinant Laccase (rLaccase) was added to the culture medium. Thus, our results suggest that laccase activity must be considered when performing microbial TNT remediation.

Anti-genotoxic and anti-mutagenic activity of Escherichia coli Nissle 1917 as assessed by in vitro tests

Anti-genotoxic or anti-mutagenic activity has been described for a number of Gram-positive probiotic bacterial species. Here we present evidence that Gram-negative Escherichia coli Nissle 1917 (EcN) also displays anti-genotoxic/anti-mutagenic activity, as assessed in vitro by the Comet Assay and the Ames Test, respectively. This activity was demonstrated by use of the mutagens 4-nitroquinoline-1-oxide (NQO), hydrogen peroxide (H₂O₂) and benzo(a) pyrene (B[a]P). For both assays and all three test agents the anti-genotoxic/anti-mutagenic activity of EcN was shown to be concentration dependent. By the use of extracts of bacteria that were inactivated by various procedures (heat treatment, ultrasound sonication or ultraviolet light irradiation), mechanistic explanations could be put forward. The proposed mechanisms were enforced by treating the bacterial material with proteinase K prior to testing. The mutagen H₂O₂ is most likely inactivated by enzymic activity, with catalase a likely candidate, while several explanations can be put forward for inactivation of B[a]P. NQO is most likely inactivated by metabolising enzymes, since the formation of the metabolite 4-aminoquinoline could be demonstrated. In conclusion, the in vitro results presented here make a strong case for antimutagenic properties of EcN.

Effects of long-term straw incorporation on lignin accumulation and its association with bacterial laccase-like genes in arable soils

In this study, we aimed to investigate lignin accumulation and its relationship with the composition of bacterial laccase-like genes in three arable lands (i.e., upland limestone soil (UL), upland red soil (UR), and upland-paddy rotation red soil (UPR)), which are subjected to long-term straw incorporation. After 9-13 years of straw incorporation, the lignin content significantly increased from 337.1, 414.5, and 201.6 mg/kg soil to 2096.5, 2092.4, and 1972.2 mg/kg soil in UL, UR, and UPR, respectively. The dominant lignin monomer changed from vanillyl (V)-type to cinnamyl (C)-type in UR. Both V- and C-types were the dominant monomers in UPR, and V-type monomer remained the dominant monomer in UL. Compared with the treatment without straw, straw incorporation significantly promoted the activity of laccase enzyme and the abundance of bacterial laccase-like genes in all soils. The redundancy analysis showed that the main influencing factors on lignin accumulation patterns with straw incorporation were the laccase enzyme activity, nitrogen availability, and some specific bacterial communities possessing the laccase-like genes (e.g., Thermotogae and Acidobacteria). The variation partitioning analysis confirmed that the strongest influencing factor on lignin accumulation was the composition of bacterial laccase-like genes (explained 31.4% of variance). The present study provides novel insights into the importance of bacterial laccase-like genes in shaping lignin monomer accumulation with straw incorporation in arable soils.

An enzymatic system for decolorization of wastewater dyes using immobilized CueO laccase-like multicopper oxidase on poly-3-hydroxybutyrate

The presence of synthetic dyes in wastewaters generated by the textile industry constitutes a serious environmental and health problem that urges the scientific community on an appropriate action. As a proof‐of‐concept, we have developed a novel approach to design enzymatic bioreactors with the ability to decolorize dye solutions through the immobilization of the bacterial CueO laccase‐like multicopper oxidase from Escherichia coli on polyhydroxybutyrate (PHB) beads by making use of the BioF affinity tag. The decolorization efficiency of the system was characterized by a series of parameters, namely maximum enzyme adsorption capacity, pH profile, kinetic constants, substrate range, temperature and bioreactor recycling. Depending on the tested dye, immobilization increased the catalytic activity of CueO by up to 40‐fold with respect to the soluble enzyme, reaching decolorization efficiencies of 45–90%. Our results indicate that oxidase bioreactors based on polyhydroxyalkanoates are a promising alternative for the treatment of coloured industrial wastewaters.

Electron transfer rate analysis of a site-specifically wired copper oxidase

Electron transfer kinetic parameters of site-specifically wired copper oxidase were investigated.

Bacterial laccase: recent update on production, properties and industrial applications

Laccases (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) are multi-copper enzymes which catalyze the oxidation of a wide range of phenolic and non-phenolic aromatic compounds in the presence or absence of a mediator. Till date, laccases have mostly been isolated from fungi and plants, whereas laccase from bacteria has not been well studied. Bacterial laccases have several unique properties that are not characteristics of fungal laccases such as stability at high temperature and high pH. Bacteria produce these enzymes either extracellularly or intracellularly and their activity is in a wide range of temperature and pH. It has application in pulp biobleaching, bioremediation, textile dye decolorization, pollutant degradation, biosensors, etc. Hence, comprehensive information including sources, production conditions, characterization, cloning and biotechnological applications is needed for the effective understanding and application of these enzymes at the industrial level. The present review provides exhaustive information of bacterial laccases reported till date.

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

Bacterial laccase CueO from Escherichia coli can oxidize polycyclic aromatic hydrocarbons (PAHs); however, its application in the remediation of PAH-contaminated soil mainly suffers from a low oxidation rate and copper dependence. It was reported that a laccase with a higher redox potential tended to have a higher oxidation rate; thus, the present study investigated the oxidation of PAHs using another bacterial laccase CotA from Bacillus subtilis with a higher redox potential (525 mV) than CueO (440 mV). Recombinant CotA was overexpressed in E. coli and partially purified, exhibiting a higher laccase-specific activity than CueO over a broad pH and temperature range. CotA exhibited moderate thermostability at high temperatures. CotA oxidized PAHs in the absence of exogenous copper. Thereby, secondary heavy metal pollution can be avoided, another advantage of CotA over CueO. Moreover, this study also evaluated some unexplained phenomena in our previous study. It was observed that the oxidation of PAHs with bacterial laccases can be promoted by copper. The partially purified bacterial laccase oxidized only two of the 15 tested PAHs, i.e., anthracene and benzo[a]pyrene, indicating the presence of natural redox mediators in crude cell extracts. Overall, the recombinant CotA oxidizes PAHs with high laccase activity and copper independence, indicating that CotA is a better candidate for the remediation of PAHs than CueO. Besides, the findings here provide a better understanding of the oxidation of PAHs using bacterial laccases.

Laccases of prokaryotic origin: enzymes at the interface of protein science and protein technology

The ubiquitous members of the multicopper oxidase family of enzymes oxidize a range of aromatic substrates such as polyphenols, methoxy-substituted phenols, amines and inorganic compounds, concomitantly with the reduction of molecular dioxygen to water. This family of enzymes can be broadly divided into two functional classes: metalloxidases and laccases. Several prokaryotic metalloxidases have been described in the last decade showing a robust activity towards metals, such as Cu(I), Fe(II) or Mn(II) and have been implicated in the metal metabolism of the corresponding microorganisms. Many laccases, with a superior efficiency for oxidation of organic compounds when compared with metals, have also been identified and characterized from prokaryotes, playing roles that more closely conform to those of intermediary metabolism. This review aims to present an update of current knowledge on prokaryotic multicopper oxidases, with a special emphasis on laccases, anticipating their enormous potential for industrial and environmental applications.

Occurrence of lignin degradation genotypes and phenotypes among prokaryotes

A number of prokaryotes actively contribute to lignin degradation in nature and their activity could be of interest for many applications including the production of biogas/biofuel from lignocellulosic biomass and biopulping. This review compares the reliability and efficiency of the culture-dependent screening methods currently used for the isolation of ligninolytic prokaryotes. Isolated prokaryotes exhibiting lignin-degrading potential are presented according to their phylogenetic groups. With the development of bioinformatics, culture-independent techniques are emerging that allow larger-scale data mining for ligninolytic prokaryotic functions but today, these techniques still have some limits. In this work, two phylogenetic affiliations of isolated prokaryotes exhibiting ligninolytic potential and laccase-encoding prokaryotes were determined on the basis of 16S rDNA sequences, providing a comparative view of results obtained by the two types of screening techniques. The combination of laboratory culture and bioinformatics approaches is a promising way to explore lignin-degrading prokaryotes.