Isolation and characterization of novel pI 4.8 MnP isoenzyme from white-rot fungus Irpex lacteus

Metabolic regulation mechanism of Trametes gibbosa CB_1 on lignin

White rot fungi can degrade lignin and play a significant role in the recycling of carbon resources for environmental protection. Trametes gibbosa is the main white rot fungus in Northeast China. The main acids produced by T. gibbosa degradation, include long-chain fatty acids, lactic acid, succinic acid, and some small molecular compounds for example benzaldehyde. A variety of proteins respond to lignin stress and play an important role in xenobiotics metabolism, metal ion transport, and redox. Coordinated regulation and detoxification activation of H₂O₂ produced in oxidative stress by peroxidase coenzyme system and Fenton reaction. The Dioxygenase cleavage pathway and β-ketoadipic acid pathway are the main oxidation pathways of lignin degradation, which mediate the entry of "COA" into the TCA cycle. In the joint action of hydrolase and coenzyme, cellulose, hemicellulose, and other polysaccharides are degraded and finally converted to glucose to participate in energy metabolism. The expression of the laccase (Lcc_1) protein was verified by E. coli. Also, the Lcc_1 overexpression mutant was established. The morphology of mycelium was dense and the lignin degradation rate was improved. We completed the first non-directional mutation of in T. gibbosa. It also improved the mechanism of T. gibbosa in response to lignin stress.

Catalytic properties of a short manganese peroxidase from Irpex lacteus F17 and the role of Glu166 in the Mn2+-independent activity

Il-MnP1 (GenBank: AGO86670.2) has been confirmed by sequence analysis as a short manganese peroxidase (MnP) from Irpex lacteus F17 (CCTCC AF 2014020). To investigate the catalytic properties, the oxidation of typical aromatic substrates and the pathways of guaiacol oxidation by Il-MnP1, both in the presence and absence of Mn²⁺ at either pH 4.0 or pH 7.4, were analyzed. Results showed that Il-MnP1 exhibited higher oxidative activity in the presence of Mn²⁺ than in the absence of Mn²⁺ toward the majority of the selected substrates at pH 4.0. Additionally, the similar product compositions suggested that the oxidation of guaiacol mainly belongs to a series of polymeric reactions of radicals initiated by Il-MnP1, whether they were in the presence and absence of Mn²⁺ at either pH 4.0 or 7.4. Furthermore, two variants (E166G, E166Q) were found using site-directed mutagenesis, to improve the Mn²⁺-independent oxidative activity significantly. The catalytic efficiency (K_cat/K_m) of E166G and E166Q in 2, 6-dimethoxyphenol oxidation was higher than Il-MnP1 by 170 and 34 times, respectively. The study revealed certain differences in catalytic properties between Mn²⁺ dependent and independent oxidation by Il-MnP1. More importantly, a residue (E166) was related to the Mn²⁺-independent activity of a short MnP.

Characterization of ligninolytic enzyme production in white-rot wild fungal strains suitable for kraft pulp bleaching

Fungal strains identified by phylogenetic analysis of the ITS rDNA region as Trametes versicolor (CMU-TA01), Irpex lacteus (CMU-84/13), and Phlebiopsis sp. (CMU-47/13) are able to grow on and bleach kraft pulp (KP) in a simple solid-state fermentation (SSF) assay conducted in Petri dishes. Kappa number reductions obtained with Phlebiopsis sp. (48.3%), T. versicolor (43%), and I. lacteus (39.3%), evidence their capability for lignin breakdown. Scanning electron microscopy images of KP fibers from SSF assays demonstrated increased roughness and striation, evidencing significant cell wall modification. T. versicolor produces laccase (Lac), manganese peroxidase (MnP), and lignin peroxidase (LiP) in potato dextrose broth (PDB), PDB + CuSO₄, and PDB + KP, whereas Phlebiopsis sp. and I. lacteus showed no Lac and low LiP activities in all media. Compared to PDB, the highest increase in Lac (7.25-fold) and MnP (2.37-fold) activities in PDB + CuSO₄ occur in T. versicolor; for LiP, the greatest changes (6.95-fold) were observed in I. lacteus. Incubation in PDB + KP shows significant increases in Lac and MnP for T. versicolor, MnP and LiP for Phlebiopsis sp., and none for I. lacteus. SSF assays in Petri plates are a valuable tool to select fungi that are able to delignify KP. Here, delignification by Phlebiopsis sp. of this substrate is reported for the first time, and MnP activity was strongly associated with the delignification ability of the studied strains. The obtained results suggest that the studied fungal strains have biotechnological potential for use in the paper industry.

Oxidation of a non-phenolic lignin model compound by two Irpex lacteus manganese peroxidases: evidence for implication of carboxylate and radicals

BACKGROUND

Manganese peroxidase is one of the Class II fungal peroxidases that are able to oxidize the low redox potential phenolic lignin compounds. For high redox potential non-phenolic lignin degradation, mediators such as GSH and unsaturated fatty acids are required in the reaction. However, it is not known whether carboxylic acids are a mediator for non-phenolic lignin degradation.

RESULTS

The white rot fungus Irpex lacteus is one of the most potent fungi in degradation of lignocellulose and xenobiotics. Two manganese peroxidases (IlMnP1 and IlMnP2) from I. lacteus CD2 were over-expressed in Escherichia coli and successfully refolded from inclusion bodies. Both IlMnP1 and IlMnP2 oxidized the phenolic compounds efficiently. Surprisingly, they could degrade veratryl alcohol, a non-phenolic lignin compound, in a Mn²⁺-dependent fashion. Malonate or oxalate was found to be also essential in this degradation. The oxidation of non-phenolic lignin was further confirmed by analysis of the reaction products using LC-MS/MS. We proved that Mn²⁺ and a certain carboxylate are indispensable in oxidation and that the radicals generated under this condition, specifically superoxide radical, are at least partially involved in lignin oxidative degradation. IlMnP1 and IlMnP2 can also efficiently decolorize dyes with different structures.

CONCLUSIONS

We provide evidence that a carboxylic acid may mediate oxidation of non-phenolic lignin through the action of radicals. MnPs, but not LiP, VP, or DyP, are predominant peroxidases secreted by some white rot fungi such as I. lacteus and the selective lignocellulose degrader Ceriporiopsis subvermispora. Our finding will help understand how these fungi can utilize MnPs and an excreted organic acid, which is usually a normal metabolite, to efficiently degrade the non-phenolic lignin. The unique properties of IlMnP1 and IlMnP2 make them good candidates for exploring molecular mechanisms underlying non-phenolic lignin compounds oxidation by MnPs and for applications in lignocellulose degradation and environmental remediation.

Expression of a fungal manganese peroxidase in Escherichia coli: a comparison between the soluble and refolded enzymes

BACKGROUND

Manganese peroxidase (MnP) from Irpex lacteus F17 has been shown to have a strong ability to degrade recalcitrant aromatic pollutants. In this study, a recombinant MnP from I. lacteus F17 was expressed in Escherichia coli Rosetta (DE3) in the form of inclusion bodies, which were refolded to achieve an active enzyme. Further, we optimized the in vitro refolding conditions to increase the recovery yield of the recombinant protein production. Additionally, we attempted to express recombinant MnP in soluble form in E. coli, and compared its activity with that of refolded MnP.

RESULTS

Refolded MnP was obtained by optimizing the in vitro refolding conditions, and soluble MnP was produced in the presence of four additives, TritonX-100, Tween-80, ethanol, and glycerol, through incubation at 16 °C. Hemin and Ca²⁺ supplementation was crucial for the activity of the recombinant protein. Compared with refolded MnP, soluble MnP showed low catalytic efficiencies for Mn²⁺ and H₂O₂ substrates, but the two enzymes had an identical, broad range substrate specificity, and the ability to decolorize azo dyes. Furthermore, their enzymatic spectral characteristics were analysed by circular dichroism (CD), electronic absorption spectrum (UV-VIS), fluorescence and Raman spectra, indicating the differences in protein conformation between soluble and refolded MnP. Subsequently, size exclusion chromatography (SEC) and dynamic light scattering (DLS) analyses demonstrated that refolded MnP was a good monomer in solution, while soluble MnP predominantly existed in the oligomeric status.

CONCLUSIONS

Our results showed that two forms of recombinant MnP could be expressed in E. coli by varying the culture conditions during protein expression.

Induction of Laccase, Lignin Peroxidase and Manganese Peroxidase Activities in White-Rot Fungi Using Copper Complexes

Ligninolytic enzymes, such as laccase, lignin peroxidase and manganese peroxidase, are biotechnologically-important enzymes. The ability of five white-rot fungal strains Daedaleopsis confragosa, Fomes fomentarius, Trametes gibbosa, Trametes suaveolens and Trametes versicolor to produce these enzymes has been studied. Three different copper(II) complexes have been prepared ((Him)[Cu(im)₄(H₂O)₂](btc)·3H₂O, where im = imidazole, H₃btc = 1,3,5-benzenetricarboxylic acid, [Cu₃(pmdien)₃(btc)](ClO₄)₃·6H₂O) and [Cu₃(mdpta)₃(btc)](ClO₄)₃·4H₂O, where pmdien = N,N,N′,N′′,N′′-pentamethyl-diethylenetriamine and mdpta = N,N-bis-(3-aminopropyl)methyl- amine), and their potential application for laccase and peroxidases induction have been tested. The enzyme-inducing activities of the complexes were compared with that of copper sulfate, and it has been found that all of the complexes are suitable for the induction of laccase and peroxidase activities in white-rot fungi; however, the newly-synthesized complex M1 showed the greatest potential for the induction. With respect to the different copper inducers, this parameter seems to be important for enzyme activity, which depends also on the fungal strains.

Induction, purification and characterization of a novel manganese peroxidase from Irpex lacteus CD2 and its application in the decolorization of different types of dye

Manganese peroxidase (MnP) is the one of the important ligninolytic enzymes produced by lignin-degrading fungi which has the great application value in the field of environmental biotechnology. Searching for new MnP with stronger tolerance to metal ions and organic solvents is important for the maximization of potential of MnP in the biodegradation of recalcitrant xenobiotics. In this study, it was found that oxalic acid, veratryl alcohol and 2,6-Dimehoxyphenol could stimulate the synthesis of MnP in the white-rot fungus Irpex lacteus CD2. A novel manganese peroxidase named as CD2-MnP was purified and characterized from this fungus. CD2-MnP had a strong capability for tolerating different metal ions such as Ca2+, Cd2+, Co2+, Mg2+, Ni2+ and Zn2+ as well as organic solvents such as methanol, ethanol, DMSO, ethylene glycol, isopropyl alcohol, butanediol and glycerin. The different types of dyes including the azo dye (Remazol Brilliant Violet 5R, Direct Red 5B), anthraquinone dye (Remazol Brilliant Blue R), indigo dye (Indigo Carmine) and triphenylmethane dye (Methyl Green) as well as simulated textile wastewater could be efficiently decolorized by CD2-MnP. CD2-MnP also had a strong ability of decolorizing different dyes with the coexistence of metal ions and organic solvents. In summary, CD2-MnP from Irpex lacteus CD2 could effectively degrade a broad range of synthetic dyes and exhibit a great potential for environmental biotechnology.

Degradation of alkylphenols by white rot fungus Irpex lacteus and its manganese peroxidase

Alkylphenols are common endocrine disrupters that are produced from the degradation of widely used surfactants. Since they cause various harmful effects on aquatic life and in humans, they should be removed from the environments being contaminated. White rot fungus Irpex lacteus can completely degrade 100 mg/L of octylphenol, nonylphenol, and phenylphenol during 1 day of incubation in the complex YMG medium, which was the highest degrading capability among nine strains of white rot fungi tested. In the N-limited Kirk's basal salts medium, I. lacteus could degrade almost 100 % of 100 mg/L octylphenol and nonylphenol in 1 h, and exhibited a high activity of manganese peroxidase (MnP; 1,790 U/L). MnP of I. lacteus was purified by ion exchange chromatography, and this degraded 99 % of 50 mg/L octylphenol and removed 80 % of estrogenic activity in 2 hours. In addition, the purified MnP (10 U/mL) degraded over 90 % of 50 mg/L nonylphenol in 1 h.