Characterization of a Highly Thermostable and Organic Solvent-Tolerant Copper-Containing Polyphenol Oxidase with Dye-Decolorizing Ability from Kurthia huakuii LAM0618T

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

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

Preparation and characterization of a laccase-like enzyme from Thermomicrobium roseum

In this study, a laccase-like gene from Thermomicrobium roseum DSM 5159 (TrLac-like) (NCBI: WP_012642205.1) was recombinantly expressed in Bacillus subtilis WB600. The optimum temperature and pH for TrLac-like were 50 °C and 6.0, respectively. TrLac-like showed high tolerance to mixed systems of water and organic solvents, indicating its potential for large-scale application in various industries. It showed 36.81 % similarity with YlmD from Geobacillus stearothermophilus (PDB:6T1B) in sequence alignment; therefore, 6T1B was employed as the template for homology modeling. To improve catalytic efficiency, amino acid substitutions within 5 Å of the inosine ligand were simulated to reduce the binding energy and promote substrate affinity. Single and double substitutions (44 and 18, respectively) were prepared, and the catalytic efficiency of the mutant A248D was increased to approximately 110-fold that of the wild type, while the thermal stability was maintained. Bioinformatics analysis revealed that the significant improvement in catalytic efficiency could be attributed to the formation of new hydrogen bonds between the enzyme and substrate. With a further decrease in the binding energy, the catalytic efficiency of the multiple mutant H129N/A248D was approximately 14-fold higher than that of the wild type but lower than that of the single mutant A248D. This is possibly because k_cat also decreased with the decrease of K_m; consequently, the substrate could not be released in time owing to the enzyme with the combination mutation not being able to release the substrate at a high rate.

Effects of Sodium Nitrate and Coated Methionine on Lactation Performance, Rumen Fermentation Characteristics, Amino Acid Metabolism, and Microbial Communities in Lactating Buffaloes

Sodium nitrate is used as a non-protein nitrogen supplement while methionine is considered as a common methionine additive for ruminants. This study investigated the effects of sodium nitrate and coated methionine supplementation on milk yield, milk composition, rumen fermentation parameters, amino acid composition, and rumen microbial communities in lactating buffaloes. Forty mid-lactation multiparous Murrah buffaloes within the initial days in milk (DIM) = 180.83 ± 56.78 d, milk yield = 7.63 ± 0.19 kg, body weight = 645 ± 25 kg were selected and randomly allocated into four groups (N = 10). All of animals received the same total mixed ratio (TMR) diet. Furthermore, the groups were divided into the control group (CON), 70 g/d sodium nitrate group (SN), 15 g/d palmitate coated L-methionine group (MET), and 70 g/d sodium nitrate +15 g/d palmitate coated L-methionine group (SN+MET). The experiment lasted for six weeks, including two weeks of adaption. The results showed that most rumen-free amino acids, total essential amino acids, and total amino acids in Group SN increased (p < 0.05), while the dry matter intake (DMI) and rumen acetate, propionate, valerate, and total volatile fatty acids (TVFA) in Group MET decreased (p < 0.05). However, there was no significant difference in milk yield, milk protein, milk fat, lactose, total solid content, and sodium nitrate residue in milk among groups (p > 0.05). Group SN+MET had a decreased rumen propionate and valerate (p < 0.05), while increasing the Ace, Chao, and Simpson indices of alpha diversity of rumen bacteria. Proteobacteria and Actinobacteriota were significantly increased (p < 0.05) in Group SN+MET, but Bacteroidota, and Spirochaetota were decreased (p < 0.05). In addition, Group SN+MET also increased the relative abundance of Acinetobacter, Lactococcus, Microbacterium, Chryseobacterium, and Klebsiella, which were positively correlated with cysteine and negatively correlated with rumen acetate, propionate, valerate, and TVFA. Rikenellaceae_RC9_gut_group was identified as a biomarker in Group SN. Norank_f__UCG-011 was identified as a biomarker in Group MET. Acinetobacter, Kurthia, Bacillus, and Corynebacterium were identified as biomarkers in Group SN+MET. In conclusion, sodium nitrate increased rumen free amino acids, while methionine decreased dry matter intake (DMI) and rumen volatile fatty acids. The combined use of sodium nitrate and methionine enriched the species abundance of microorganisms in the rumen and affected the composition of microorganisms in the rumen. However, sodium nitrate, methionine, and their combination had no significant effect on the milk yield and milk composition. It was suggested that the combined use of sodium nitrate and methionine in buffalo production was more beneficial.

Formation of recombinant bifunctional fusion protein: A newer approach to combine the activities of two enzymes in a single protein

The tissue of insects, pests, and fungi has a chitin layer followed by protein in the cell membrane. The complete biodegradation of chitin and protein-present in the waste requires the action of two enzymes, namely chitinase, and protease. Combining chitinase and protease in a single protein/enzyme will serve as a bifunctional enzyme that can efficiently degrade the chitin and protein-rich biomass. The present study was aimed to fuse these two enzymes to produce a single protein and study the kinetics of the recombinant fusion protein. A chitinase and alkaline protease genes were isolated, cloned, and expressed successfully as a fusion product in heterologous host Escherichia coli. The two native genes were successfully fused in E.coli by using flexible glycine–serine (G₄S)₂ linker (GGGGS, GS linker). The recombinant fusion protein in E.coli showed hydrolyzed chitin and protein on chitin and bovine serum albumin agar plates confirming the successful cloning and expression of chitinase and protease enzymes in a single fusion protein. The common pUC18-T7 mini vector with the ompA signal sequence helps the extracellular expression of fusion protein efficiently. The native gel electrophoresis revealed a molecular mass of purified protein as 92.0 kDa. The fusion protein’s maximal chitinase and protease activity occurred at pH 5.0 and 8.0 and 30 ⁰C, respectively resembling the individual enzymes’. In the kinetic studies of the fusion protein, it was observed that the presence of metal ions such as Cu²⁺, Na²⁺, and Ca²⁺; significantly enhanced the enzyme activities while organic solvents oxidants and chemicals have drastically affected the activities of both the enzymes in the fusion protein. No such fusion protein has been produced in a heterologous host yet. The reports on fusion protein with biomass-degrading capacity are also scarce. This is probably the first report of a bifunctional chitinase/protease expressed in E. coli.

Functional assignment to hypothetical proteins in Orientia tsutsugamushistrain Ikeda

Orientia tsutsugamushi(O. tsutsugamushi) is an intracellular bacterial pathogen which causes zoonosis scrub typhus in humans. Genome of O. tsutsugamushi strain Ikeda contains 214 hypothetical proteins (HPs) which is nearly 20% of the total proteins. Domain and family based functional analysis of HPs results in the annotation of 44 hypothetical proteins. The annotated HPs were classified in to five main classes namely, gene expression and regulation, transport, metabolism, cell signaling and proteolysis. Thus, computational analysis of HPs helps to understand their putative roles in various biological and cellular processes, including pathogenesis for further consideration as potential therapeutic targets.

Characterization of a Recombinant Laccase B from Trametes hirsuta MX2 and Its Application for Decolorization of Dyes

Trametes hirsuta is able to secrete laccase isoenzymes including constitutive and inducible forms, and has potential application for bioremediation of environmental pollutants. Here, an inducible group B laccase from T. hirsuta MX2 was heterologously expressed in Pichia pastoris, and its yield reached 2.59 U/mL after 5 days of methanol inducing culture. The optimal pH and temperature of recombinant laccase (rLac1) to 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) were 2.5 and 60 °C, respectively. Metal ions showed different effect on rLac1 which Mg²⁺, Cu²⁺, and K⁺ increased enzyme activity as their concentration increased, whereas Zn²⁺, Na⁺, and Fe²⁺ inhibited enzyme activity as their concentration increased. rLac1 showed good tolerance to organic solvents, and more than 42% of its initial activity remained in 10% organic solvents. Additionally, rLac1 exhibited a more efficient decolorization ability for remazol brilliant blue R (RBBR) than for acid red 1 (AR1), crystal violet (CV), and neutral red (NR). Molecular docking results showed RBBR has a stronger binding affinity with laccase than other dyes by interacting with substrate binding cavity of enzyme. The results indicated rLac1 may be a potential candidate for dye removal from textile wastewater.

An Engineered Thermostable Laccase with Great Ability to Decolorize and Detoxify Malachite Green

Laccases can catalyze the remediation of hazardous synthetic dyes in an eco-friendly manner, and thermostable laccases are advantageous to treat high-temperature dyeing wastewater. A novel laccase from Geothermobacter hydrogeniphilus (Ghlac) was cloned and expressed in Escherichia coli. Ghlac containing 263 residues was characterized as a functional laccase of the DUF152 family. By structural and biochemical analyses, the conserved residues H78, C119, and H136 were identified to bind with one copper atom to fulfill the laccase activity. In order to make it more suitable for industrial use, Ghlac variant Mut2 with enhanced thermostability was designed. The half-lives of Mut2 at 50 °C and 60 °C were 80.6 h and 9.8 h, respectively. Mut2 was stable at pH values ranging from 4.0 to 8.0 and showed a high tolerance for organic solvents such as ethanol, acetone, and dimethyl sulfoxide. In addition, Mut2 decolorized approximately 100% of 100 mg/L of malachite green dye in 3 h at 70 °C. Furthermore, Mut2 eliminated the toxicity of malachite green to bacteria and Zea mays. In summary, the thermostable laccase Ghlac Mut2 could effectively decolorize and detoxify malachite green at high temperatures, showing great potential to remediate the dyeing wastewater.

Production and characterization of a novel thermostable laccase from Bacillus licheniformis VNQ and its application in synthesis of bioactive 1,4-naphthoquinones

Bacterial laccases have proven to be a potential biocatalyst for various industrial applications due to their remarkable catalytic and stability properties. In this study, a novel thermostable laccase was produced from the bacterium Bacillus licheniformis VNQ by submerged fermentation. The specific activity of crude and purified laccase was found to be 13.17 U mg^-1 and 83.47 U mg^-1, respectively. The enzyme possessed a molecular mass of ∼48 kDa when characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum temperature and pH for enzyme activity was determined to be 55°C and 5.0, respectively. The enzyme was considered to be thermo-tolerant as it possessed a half-life of 4 h at 70°C. The enzyme was utilized for the oxidative biotransformation of in situ synthesized p-quinones to biologically active compounds, 1,4-naphthoquinone and its derivative. The obtained products were characterized using nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS) analysis. A high yield of naphthoquinones (74.93 ± 1.2%) with 1,4-naphthoquinone (60.61 ± 1.0%), and its derivative 2-hydroxy-1,4-naphthoquinone (14.32 ± 0.2%) was obtained at the optimized reaction conditions.

Screening of Novel Laccase Producers-Isolation and Characterization of Cold-Adapted Laccase from Kabatiella bupleuri G3 Capable of Synthetic Dye Decolorization

Psychrophilic laccases catalyzing the bond formation in mild, environmentally friendly conditions are one of the biocatalysts at the focus of green chemistry. Screening of 41 cold-adapted strains of yeast and yeast-like fungi revealed a new laccase-producing strain, which was identified as Kabatiella bupleuri G3 IBMiP according to the morphological characteristics and analysis of sequences of the D1/D2 regions of 26S rDNA domain and the ITS1-5,8S-ITS2 region. The extracellular activity of laccase in reaction with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) at the optimal pH 3.5 was 215 U/L after 15 days of growth in a medium with waste material and 126 U/L after 25 days of cultivation in a defined medium. Copper (II) ions (0.4 mM), Tween 80 (1.0 mM) and ascorbic acid (5.0 mM) increased the production of laccase. The optimum temperature for enzyme operation is in the range of 30-40 °C and retains over 60% of the maximum activity at 10 °C. New laccase shows high thermolability-half-life at 40 °C was only 60 min. Enzyme degradation of synthetic dyes was the highest for crystal violet, i.e., 48.6% after 1-h reaction with ABTS as a mediator. Outcomes of this study present the K. bupleuri laccase as a potential psychrozyme for environmental and industrial applications.

Optimisation of the Production and Bleaching Process for a New Laccase from Madurella mycetomatis, Expressed in Pichia pastoris: from Secretion to Yielding Prominent

Laccases are polyphenol oxidoreductases used in a number of industrial applications. Due to the increasing demand for these "green catalysis" enzymes, the identification and biochemical characterisation of their novel properties is essential. In our study, cloned Madurella mycetomatis laccase (mmlac) genes were heterologously expressed in the methylotrophic yeast host Pichia pastoris. The high yield of the active recombinant protein in P. pastoris demonstrates the efficiency of a reliably constructed plasmid to express the laccase gene. The optimal biochemical conditions for the successfully expressed MmLac enzyme were identified. Detailed structural properties of the recombinant laccase were determined, and its utility in decolourisation and textile bleaching applications was examined. MmLac demonstrates good activity in an acidic pH range (4.0-6.0); is stable in the presence of cationic metals, organic solvents and under high temperatures (50-60 °C); and is stable for long-term storage at - 20 °C and - 80 °C for up to eight weeks. The structural analysis revealed that the catalytic residues are partially similar to other laccases. MmLac resulted in an increase in whiteness, whilst demonstrating high efficiency and stability and requiring the input of fewer chemicals. The performance of this enzyme makes it worthy of investigation for use in textile biotechnology applications, as well as within environmental and food technologies.

Bacterial laccase of Anoxybacillus ayderensis SK3-4 from hot springs showing potential for industrial dye decolorization

Introduction

Laccases are green biocatalysts that possess attractive for the treatment of resistant environmental pollutants and dye effluents.

Purpose

To exploit the laccase of Anoxybacillus ayderensis SK3-4 that possesses dye decolorization ability at room and higher temperature, we characterized the enzyme in considerable detail and investigated its ability to decolorize different dyes.

Results

A bacterial laccase gene designed as LacAn from Anoxybacillus ayderensis SK3-4 of hot springs was cloned and expressed in Escherichia coli. LacAn is a monomeric protein with a molecular weight of 29.8 kDa. The optimum pH and temperature for syringaldazine oxidation were 7.0 and 75 °C, respectively. LacAn was stable at pH values ranging from 6.5 to 8.5 above 65 °C. The enzyme activity was significantly enhanced by Cu2+ and Mg2+ but inhibited by Zn2+ and Fe2+. Furthermore, LacAn showed high decolorization capability toward five dyes (direct blue 6, acid black 1, direct green 6, direct black 19, and acid blue 93) in the absence of redox mediators. It also demonstrated a wide temperature range, and it can retain its high decolorization ability even at high temperatures.

Conclusions

These properties including better enzymatic properties and efficiency to decolorize dyes demonstrate that the bacterial laccase LacAn has potentials for further industrial applications.

Heterologous Expression of Laccase From Lentinula edodes in Pichia pastoris and Its Application in Degrading Rape Straw

Rape straw cannot be efficiently degraded and utilized by ruminants due to its severe lignification and complex cross-linked structure between fiber and lignin. The laccases can catalyze the inter-unit bond cleavage in lignin substrates. Therefore, this study investigated the recombinant laccase from Lentinula edodes (LeLac) and its application in degrading rape straw. The LeLac was expressed using Pichia pastoris. It had the maximum activity at 60°C and pH 3.0 using ABTS as substrate and at 50°C and pH 4.0 using o-tolidine as substrate. The LeLac exhibited preferential oxidation of ABTS and featured resistance to high temperature, but relatively poor thermal stability. The LeLac activity could be strengthened by Cu²⁺ in dose-dependent manners. The LeLac could tolerate 15% of ethanol and methanol. The optimal pH for the lignin degradation of rape straw acid detergent fiber (ADF) by LeLac was 4.0. The LeLac could improve the cellulose enzymolysis of rape straw ADF by degrading its lignin. Relatively fewer lignin but more soluble phenols from original rape straw were removed by LeLac. The enhancement of enzymatic hydrolysis in original rape straw should be a combined result of polyphenols removal and lignin degradation caused by LeLac. This study demonstrated that the LeLac could improve the utilization of rape straw by degrading its lignin, meanwhile it’s worth noting that removing the soluble phenols by LeLac might also play an important role.

Refolding, characterization, and dye decolorization ability of a highly thermostable laccase from Geobacillus sp. JS12

A putative laccase gene (lacG) from Geobacillus sp. JS12 was cloned and expressed as a fusion protein with six histidine residues in Escherichia coli BL21 (DE3) cells, and the protein was primarily found in inclusion bodies. The resulting insoluble proteins were solubilized with 6 M guanidine HCl and refolded using an on-column refolding procedure. Ni-chelation affinity chromatography found the laccase to be a 30 kDa monomeric protein. Spectrophotometry and electron paramagnetic resonance (EPR) analysis indicated LacG as a multi-copper oxidase, with the usual laccase copper sites, Type 1, 2, and 3 Cu(II). The optimum pH for enzymatic activity was 3.0, 6.0, and 6.5 with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), guaiacol and 2,6-dimethoxyphenol (2,6-DMP) as the substrate, respectively. The recombinant protein displayed high thermostability, with a heat inactivation half-life of approximately 2 h at 95 °C, and an optimum temperature of 80 °C with 2,6-DMP. Catalytic efficiency (k_cat/K_m) showed that guaiacol and 2,6-DMP were highly oxidized by the enzyme. The enzymatic reaction was significantly enhanced by Co²⁺ and Mn²⁺, while activity was strongly inhibited in the presence of Fe²⁺, Zn²⁺, and thiol compounds. LacG decolorized 43% of Congo red and 14% of Malachite green, and the addition of ABTS as a redox mediator dramatically increased the dye decolorization efficiency.

Genome Sequencing Revealed the Biotechnological Potential of an Obligate Thermophile Geobacillus thermoleovorans Strain RL Isolated from Hot Water Spring

In the present study, we report the draft genome sequence of an obligate thermophile Geobacillus thermoleovorans strain RL isolated from Manikaran hot water spring located atop the Himalayan ranges, India. Strain RL grew optimally at 70 °C but not below 45 °C. The draft genome (3.39 Mb) obtained by Illumina sequencing contains 138 contigs with an average G + C content of 52.30%. RAST annotation showed that amino acid metabolism pathways were most dominant followed by carbohydrate metabolism. Genome-wide analysis using NCBI's Prokaryotic Genome Annotation Pipeline revealed that strain RL encodes for a cocktail of industrially important hydrolytic enzymes glycoside hydrolase, α-and β-glucosidase, xylanase, amylase, neopullulanase, pullulanase and lipases required for white biotechnology. In addition, the presence of genes encoding green biocatalyst multicopper polyphenol oxidase (laccase) and an anticancer enzyme l-glutaminase reflects the significance of strain RL in gray and red biotechnology, respectively. Strain RL is a thermophilic multi-enzyme encoding bacterium which could be the source for the recombinant production of biotechnologically significant enzymes. In, addition whole cells of strain RL may be used in bioremediation studies.

Production of highly thermo-tolerant laccase from novel thermophilic bacterium Bacillus sp. PC-3 and its application in functionalization of chitosan film

In this study, a novel thermophilic bacterial strain was isolated from Tattapani hot spring located in the Chhattisgarh state of India. The laccase was produced via submerged fermentation and purified by ammonium sulfate precipitation and anion exchange chromatography up to 13.7 fold. The 16S rRNA gene sequence and biochemical analysis revealed that the bacterial isolate is Bacillus sp. strain PC-3. The activity of extracellular crude laccase was determined to be 11.2 U/mL using 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) as a substrate. The SDS-PAGE revealed that the enzyme consists of single subunit with molecular size of 36 kDa. The laccase exhibited the maximum enzyme activity at temperature of 60°C and pH 7. Moreover, the laccase retained 99.1% of its original activity for 180 min and exhibited half-life of 3.75 h at 60°C. Similarly, the laccase retained 95% activity at pH 7 for 240 min and displayed significant activity at wider pH range. In addition, the laccase was used for functionalization of chitosan film and characterized for antioxidant and antimicrobial activity. Interestingly, the functionalized chitosan film showed the improved antioxidant and antimicrobial activity.

Biodetoxification of Phenolic Inhibitors from Lignocellulose Pretreatment using Kurthia huakuii LAM0618T and Subsequent Lactic Acid Fermentation

Phenolic inhibitors generated during alkaline pretreatment of lignocellulosic biomasses significantly hinder bacterial growth and subsequent biofuel and biochemical production. Water rinsing is an efficient method for removing these compounds. Nevertheless, this method often generates a great amount of wastewater, and leads to the loss of solid fiber particles and fermentable sugars. Kurthia huakuii LAM0618^T, a recently identified microorganism, was herein shown to be able to efficiently transform phenolic compounds (syringaldehyde, hydroxybenzaldehyde, and vanillin) into less toxic acids. Taking advantage of these properties, a biodetoxification method was established by inoculating K. huakuii LAM0618^T into the NH₃/H₂O₂-pretreated unwashed corn stover to degrade phenolic inhibitors and weak acids generated during the pretreatment. Subsequently, 33.47 and 17.91 g/L lactic acid was produced by Bacillus coagulans LA204 at 50 °C through simultaneous saccharification and fermentation (SSF) from 8% (w/w) of NH₃/H₂O₂-pretreated corn stover with or without K. huakuii LAM0618^T-biodetoxification, indicating biodetoxification significantly increased lactic acid titer and yield. Importantly, using 15% (w/w) of the NH₃/H₂O₂-pretreated K. huakuii LAM0618^T-biodetoxified corn stover as a substrate through fed-batch simultaneous saccharification and fermentation, high titer and high yield of lactic acid (84.49 g/L and 0.56 g/g corn stover, respectively, with a productivity of 0.88 g/L/h) were produced by Bacillus coagulans LA204. Therefore, this study reported the first study on biodetoxification of alkaline-pretreated lignocellulosic material, and this biodetoxification method could replace water rinsing for removal of phenolic inhibitors and applied in biofuel and biochemical production using the alkaline-pretreated lignocellulosic bioresources.

Biochemical characterization of a thermostable cobalt- or copper-dependent polyphenol oxidase with dye decolorizing ability from Geobacillus sp. JS12

A putative laccase-like gene, GPPO, encoding a protein of 17.2 kDa and belonging to the multicopper oxidase family, was cloned and overexpressed in Escherichia coli cells. The purified recombinant protein GPPO is homodecameric protein with a molecular weight of 171.6 kDa. GPPO was not detected the ultraviolet-visible spectroscopy (UV/Vis) spectrum of typical laccases. Co²⁺ or Cu²⁺ was essential for substrate oxidation of GPPO, and the enzyme contained 1 mol of Co or Cu per mole of protein. The optimum pH required for the oxidation of 2,2'-azino-bis(3-ethylbenzothazoline-6-sulfonate) (ABTS) and 2,6-dimethoxyphenol (DMP) was 4.5 and 5.5, respectively, and the optimum temperature was 75 °C. The half-life of heat inactivation was about 8 min at 80 °C and 90 min at 90 °C, in the presence of Cu²⁺ and Co²⁺, respectively. The catalytic efficiency (k_cat/K_m) of GPPO containing Co²⁺ was 68 times higher than that of GPPO containing Cu²⁺. The enzyme reaction was inhibited by conventional inhibitors of laccase like metal chelators and thiol compounds. GPPO incubated with Cu²⁺ or Co²⁺ for 48 h decolorizes 45% or 47% of Nile blue, respectively. This is the first report of a novel thermostable polyphenol oxidase that shows the cobalt-dependent laccase activity and dye decolorization ability.

Characterization of AiiK, an AHL lactonase, from Kurthia huakui LAM0618T and its application in quorum quenching on Pseudomonas aeruginosa PAO1

N-Acyl homoserine lactones (AHLs) act as the key quorum sensing (QS) signal molecules in gram-negative bacteria, which coordinates gene expression and then activates various processes, including biofilm formation and production of virulence factors in some pathogens. Quorum quenching (QQ), which is the inactivation of the signal molecules by means of enzymatic degradation or modification, inhibits the processes of QS rather than killing the pathogens and is a promising antipathogenic strategy to control the bacterial pathogens. In this study, an AHL lactonase gene (named aiiK) was cloned from Kurthia huakuii LAM0618^T and the AHL lactonase AiiK was expressed by Escherichia coli. AiiK exhibits a variable substrate spectrum and efficient degradation of the AHL compounds. The enzyme assays demonstrated that AiiK behaves as an AHL lactonase that can hydrolyze the lactone bond of the AHLs. The total hydrolytic efficiency of AiiK for C₁₀-HSL is 3.9 s^-1·mM^-1. AiiK can also maintain 20% activity after 12 h incubation at 37 °C and demonstrate great resistance to α-chymotrypsin, trypsin, and protease K. Furthermore, AiiK significantly inhibits the biofilm formation and attenuates extracellular proteolytic activity and pyocyanin production of Pseudomonas aeruginosa PAO1, which indicates the potential application of AiiK as a biocontrol agent or an anti-pathogenic drug.

Expression and characterization of novel laccase gene from Pandoraea sp. ISTKB and its application

In the present study, a non-blue laccase gene from previously reported lignin degrading bacterium, Pandoraea sp. ISTKB, was isolated, cloned and expressed in E. coli. Bioinformatics analysis of sequence discovered twin-arginine translocation signal sequence, copper binding motifs and presence of more random coil compare to helices and sheets in structure. The enzyme was found to be active on wide pH range and the pH optima was observed at pH 4 and 8 on substrate 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) and 2,6-Dimethoxyphenol respectively. This is a thermophilic enzyme with maximum activity around 50-70 °C. The enzyme was further characterized by spectroscopy, reaction kinetics and effect of metal ions and inhibitors were studied. Compared to laccase alone; the treatment of dyes with laccase plus mediator resulted in enhanced decolorization of crystal violet, methylene blue, azure B, carmine and Congo red but the effect of mediator was not observed on trypan blue. Laccase treatment triggered polymerization on vanillic acid (VA) and kraft lignin (KL). Laccase plus mediator treatment reversed the polymerization and resulted in transformation or degradation of VA and KL. This thermophilic and alkalophilic non-blue laccase from Pandoraea sp. ISTKB is promising with prospective biotechnological application.

Preparation of Biocolorant and Eco-Dyeing Derived from Polyphenols Based on Laccase-Catalyzed Oxidative Polymerization

Natural products have been believed to be a promising source to obtain ecological dyes and pigments. Plant polyphenol is a kind of significant natural compound, and tea provides a rich source of polyphenols. In this study, biocolorant derived from phenolic compounds was generated based on laccase-catalyzed oxidative polymerization, and eco-dyeing of silk and wool fabrics with pigments derived from tea was investigated under the influence of pH variation. This work demonstrated that the dyeing property was better under acidic conditions compared to alkalinity, and fixation rate was the best when pH value was 3. Furthermore, breaking strength of dyed fabrics sharply reduced under the condition of pH 11. Eventually, the dyeing method was an eco-friendly process, which was based on bioconversion, and no mordant was added during the process of dyeing.

Polyphenol oxidase from Pectobacterium atrosepticum: identification and cloning of gene and characteristics of the enzyme

In the present study, we attempted to elucidate if the harmful phytopathogenic bacteria of Pectobacterium genus (P. atrosepticum) possess the enzymes for oxidation of phenolic compounds. Polyphenol oxidase (laccase) activity was revealed in P. atrosepticum cell lysates. Using bioinformatic analysis, an ORF encoding a putative copper-containing polyphenol oxidase of 241 amino acids with a predicted molecular mass of 25.9 kDa was found. This protein (named Pal1) shares significant level of identity with laccases of a new type described for several bacterial species. Cloning and expression of the pal1 gene and the analysis of corresponding recombinant protein confirmed that Pal1 possessed laccase activity. The recombinant Pal1 protein was characterized in terms of substrate specificity, kinetic parameters, pH and temperature optimum, sensitivity to inhibitors and metal content. Pal1 demonstrated alkali- and thermo-tolerance. The kinetic parameters K_m and kcat for 2,6-dimethoxyphenol were 0.353 ± 0.062 mM and 98.79 ± 4.9 s^-1 , respectively. The protein displayed high tolerance to sodium azide, sodium fluoride, NaCl, SDS and cinnamic acid. The transcript level of the pal1 gene in P. atrosepticum was shown to be induced by plant-derived phenolic compound (ferulic acid) and copper sulfate.