Degradation Of Lignin In Wood Research Articles

The lignin-degrading abilities of Gelatoporia subvermispora gat1 and pex1 mutants generated via CRISPR/Cas9.

White-rot fungi efficiently degrade wood lignin; however, the mechanisms involved remain largely unknown. Recently, a forward genetics approach to identify several genes in Pleurotus ostreatus (Agaricales) in which mutations cause defects in wood lignin degradation was used. For example, pex1 encodes a peroxisome biogenesis factor and gat1 encodes a putative Agaricomycetes-specific DNA-binding transcription factor. In this study, we examined the effects of single-gene mutations in pex1 or gat1 on wood lignin degradation in another white-rot fungus, Gelatoporia (Ceriporiopsis) subvermispora (Polyporales), to investigate conserved and derived degradation mechanisms in white-rot fungi. G. subvermispora pex1 and gat1 single-gene mutant strains were generated from a monokaryotic wild-type strain, FP-90031-Sp/1, using plasmid-based CRISPR/Cas9. As in P. ostreatus, Gsgat1 mutants were nearly unable to degrade lignin sourced from beech wood sawdust medium (BWS), while Gspex1 mutants exhibited a delay in lignin degradation. We also found that the transcripts of lignin-modifying enzyme-encoding genes, mnp4, mnp5, mnp6, mnp7, and mnp11, which predominantly accumulate in FP-90031-Sp/1 cultured with BWS, were greatly downregulated in Gsgat1 mutants. Taken together, the results suggest that Gat1 may be a conserved regulator of the ligninolytic system of white-rot fungi and that the contribution of peroxisomes to the ligninolytic system may differ among species.

Targeted disruption of hir1 alters the transcriptional expression pattern of putative lignocellulolytic genes in the white-rot fungus Pleurotus ostreatus

Pleurotus ostreatus is frequently used in molecular genetics and genomic studies on white-rot fungi because various molecular genetic tools and relatively well-annotated genome databases are available. To explore the molecular mechanisms underlying wood lignin degradation by P. ostreatus, we performed mutational analysis of a newly isolated mutant UVRM28 that exhibits decreased lignin-degrading ability on the beech wood sawdust medium. We identified that a mutation in the hir1 gene encoding a putative histone chaperone, which probably plays an important role in DNA replication-independent nucleosome assembly, is responsible for the mutant phenotype. The expression pattern of ligninolytic genes was altered in hir1 disruptants. The most highly expressed gene vp2 was significantly inactivated, whereas the expression of vp1 was remarkably upregulated (300–400 fold) at the transcription level. Conversely, many cellulolytic and xylanolytic genes were upregulated in hir1 disruptants. Chromatin immunoprecipitation analysis suggested that the histone modification status was altered in the 5ʹ-upstream regions of some of the up- and down-regulated lignocellulolytic genes in hir1 disruptants compared with that in the 20b strain. Hence, our data provide new insights into the regulatory mechanisms of lignocellulolytic genes in P. ostreatus.

Peroxidase evolution in white-rot fungi follows wood lignin evolution in plants

A comparison of sequenced Agaricomycotina genomes suggests that efficient degradation of wood lignin was associated with the appearance of secreted peroxidases with a solvent-exposed catalytic tryptophan. This hypothesis is experimentally demonstrated here by resurrecting ancestral fungal peroxidases, after sequence reconstruction from genomes of extant white-rot Polyporales, and evaluating their oxidative attack on the lignin polymer by state-of-the-art analytical techniques. Rapid stopped-flow estimation of the transient-state constants for the 2 successive one-electron transfers from lignin to the peroxide-activated enzyme (k2app and k3app ) showed a progressive increase during peroxidase evolution (up to 50-fold higher values for the rate-limiting k3app ). The above agreed with 2-dimensional NMR analyses during steady-state treatments of hardwood lignin, showing that its degradation (estimated from the normalized aromatic signals of lignin units compared with a control) and syringyl-to-guaiacyl ratio increased with the enzyme evolutionary distance from the first peroxidase ancestor. More interestingly, the stopped-flow estimations of electron transfer rates also showed how the most recent peroxidase ancestors that already incorporated the exposed tryptophan into their molecular structure (as well as the extant lignin peroxidase) were comparatively more efficient at oxidizing hardwood (angiosperm) lignin, while the most ancestral "tryptophanless" enzymes were more efficient at abstracting electrons from softwood (conifer) lignin. A time calibration of the ancestry of Polyporales peroxidases localized the appearance of the first peroxidase with a solvent-exposed catalytic tryptophan to 194 ± 70 Mya, coincident with the diversification of angiosperm plants characterized by the appearance of dimethoxylated syringyl lignin units.

Photostabilization mechanisms of the main wood photostabilizers from the heartwood extract in Acacia confusa: okanin and melanoxetin

Flavonoids are secondary metabolites with abilities to reduce the thermal- and photoinduced degradation of polymeric materials. Previous studies indicated that the flavonoids in Acacia confusa heartwood had photostabilities that can reduce the photoinduced degradation of lignin in wood. Hence, the photostabilities and the photostabilization mechanisms of major flavonoids in A. confusa heartwood merit further study. This study demonstrates that the flavone (7,3′,4′-trihydroxy-5-methoxyflavone), flavonols (melanoxetin and 7,8,3′-trihydroxy-3,4′-dimethoxyflavone) and chalcone (okanin) in A. confusa heartwood have good UV absorptivity, singlet oxygen quenching ability and phenoxyl radical scavenging ability, in particular, the two most abundant flavonoids, melanoxetin and okanin. Additionally, okanin can quench excited lignin. Accordingly, these flavonoids can remove hazards induced during lignin photodegradation.

UJI AKTIVITAS ANTIOKSIDAN HASIL DEGRADASI LIGNIN DARI SERBUK GERGAJI KAYU KALBA (Albizia falcataria) DENGAN METODE TBA (Thio Barbituric Acid)

Antioxidants are compounds that can delay, retard or inhibit the oxidation reaction. Lignin is a natural polymer consisting of monomeric substituted phenols. Wood lignin degradation Kalba (Albizia falcataria) yields substituted phenol. The purpose of this study was to test the antioxidant activity of compounds of lignin degradation products Kalba using TBA (Thiobarbituric Acid). Wood lignin degradation products Kalba tested antioxidant activity using the TBA method. Phase test phase of this antioxidant activity is sample preparation, determination of the maximum wavelength, determination of equilibrium time, absorbance measurements and determination of the percentage of inhibition. The wavelength maximum for BHT test solution was obtained at 530 nm. The stability of absorbance achieved after 80 minutes equilibrium time. BHT test solution and sample solution containing the degradation of lignin 0.10% (w/v) increased but not as sharp as the absorbance of control, this suggests that the degradation of wood lignin Kalba have activity as an antioxidant, which relative minimize 13,70 % compare with BHT.

We've Got Chemistry Sussed

We've Got Chemistry Sussed

Selective Degradation of Wood Lignin over Noble‐Metal Catalysts in a Two‐Step Process

Breaking down is usually hard to do…︁ The direct conversion of lignin into alkanes and methanol was carried out in a two-step process (hydogenolysis and hydrogenation) involving initial treatment of white birch wood sawdust with H2 in dioxane/water/phosphoric acid using Rh/C as the catalyst. The resulting monomers and dimers obtained by selective CO hydrogenolysis were then hydrogenated in near-critical water employing Pd/C as the catalyst.

Wood plastic composites weathering: Visual appearance and chemical changes

The effects of outside and accelerated (xenon-arc and UVA) weathering on the visual appearance and chemical changes of wood plastic composite (WPC) formulations based on high density polyethylene (HDPE) and polypropylene (PP) were investigated. Colorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy (FT-IR), and pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) were employed in this study. The study showed that for both outside and accelerated weathering, longer exposure time increased the degree of color change (and lightness), carbonyl concentrations, and wood loss on weathered WPC surfaces. HDPE-based WPC exhibited decreased lightening, carbonyl concentrations, and wood content loss when compared to PP-based WPC. From this study, relationships between chemical and color changes that occurred during exterior weathering of HDPE-based WPC were established. Oxidation and degradation of wood lignin influenced WPC color changes (lightening) during weathering.

Effect of phenolic acids on manganese peroxidase-dependent peroxidation of linoleic acid and degradation of a non-phenolic lignin model compound

The influence of aromatic phenolic and non-phenolic acids on manganese peroxidase (MnP)-dependent peroxidation of linoleic acid, and oxidation of a non-phenolic lignin model compound (LMC) was studied. Phenolic compounds inhibited both the MnP-dependent lipid peroxidation (LPO) and non-phenolic LMC degradation in the system. The antioxidant activity of the aromatic compounds in the enzymatic system with MnP-dependent LPO depends on the presence of the phenolic hydroxyl groups attached to the aromatic ring structure, the methoxylation of the hydroxyl group in the ortho position in diphenolics, and number of carbon atoms in the side chain. Natural phenolic compounds inhibit the oxidation of non-phenolic lignin in the system based on MnP-mediated LPO, but do not prevent it. This result indicates that MnP-mediated LPO may play an important role in lignin degradation even in the presence of the phenolic antioxidant compounds, and supports the possibility of the involvement of LPO in the degradation of lignin in wood.

Free radical versus electron-transfer routes of oxidation of hydrocarbons by laccase/mediator systems: Catalytic or stoichiometric procedures

The oxidation of CH bonds in alkylarenes can take place by dioxygen, under catalysis by the phenol-oxidase enzyme laccase, provided that suitable mediator compounds are added. The actual oxidation of the substrate is carried out by the oxidised form of the mediator, in a non-enzymatic step. The relative efficiency of four >NOH-type mediators (HBT, HPI, VLA, NHA) has been evaluated, and compared with that of the structurally different mediator ABTS. Laccase/mediator catalysed oxidations of non-phenolic substrates can proceed via two different mechanisms. Either on monoelectronic oxidation, by the oxidised form of mediator ABTS, or, by abstraction of hydrogen atom, by a >NO radical species derived from the >NOH-type mediators. The former mechanism requires substrates with a low oxidation potential; the latter mechanism requires substrates with relatively weak CH bonds. Electrochemical and thermochemical evidence is provided (i) to explain the failure in the oxidation of specific alkylarenes and (ii) in support to the rationalisation of the experimental findings. Particular emphasis is given to discuss the effect of the mediator-to-substrate molar ratio upon the efficiency of the oxidation procedure. In order to explain why, in previous literature studies, better results may have been obtained by using the mediator in more that stoichiometric amounts, we propose the concurrent formation of degradation products from the mediator, which could be responsible for the onset of alternative oxidation pathways. A better understanding of the natural role of laccase in the oxygen-dependent degradation of lignin in wood emerges from this study.

Laccase Immunolabelling and Microanalytical Analysis of Wood Degraded byLentinus edodes

Laccase has been studied recently in both pure enzymatic, and 'enzyme plus mediator' systems described for the degradation of lignin in wood and pulp. In this study we use TEM immunolabelling probes to label the laccase enzyme and determine where the enzyme is located during wood degradation by Lentinus edodes. Wood degraded by L. edodes was also observed using two-dimensional ultraviolet analysis to determine the extent of lignin degradation, and the relationship between lignin degradation and enzymatic action. Despite extensive degradation of lignin in the wood cell wall and cell corner region of the wood, no penetration of the laccase enzyme into the wood cell wall was observed during the first eight weeks of fungal attack. Degradation of the lignin fraction of the wood cell wall by compounds of lower molecular weight than enzymes is implicated by this work.

Assessment of the tumor-initiating potential of alpha, beta-unsaturated carbonyl compounds by 32P postlabeling quantification of DNA adducts in vivo.

α,β-Unsaturated carbonyl compounds are reactive bifunctional substances which react readily with biological macromolecules, e.g., proteins and DNA. They are important industrial chemicals and environmental pollutants, formed by combustion; they are also, however, biologically formed by microorganisms during wood lignin degradation, formation of humic and fulvic acid, and by plants and animals. These compounds are present in fruit juices and in other nonalcoholic and alcoholic beverages and even in drinking water (Eder et al. 1993). The endogenous formation of these compounds during lipid peroxidation but also by other physiological and pathophysiological processes is of high significance (Witz 1989). Benedetti et al. (1984) found concentrations of 4- hydroxynonenal of about 100 μM in tissues near peroxidating membranes and Koster et al. (1986) calculated concentrations of 4.5 mM in the lipid double layer during lipid peroxidation. Furthermore, these compounds can diffuse within the endoplasmatic reticulum where they are formed associated with the lipid core to the nucleus without cytosolic detoxication (Brambilla et al. 1986). But even cytosolic conjugation with glutathione or similar compounds does not necessarily lead to detoxication since this aldehyde thiol conjugation is reversible and the adducts can dissociate and regenerate the respective α,s- unsaturated carbonyl compounds at the target site (Witz 1989).

Analysis of lignin from oak casks used for the maturation of Scotch whisky

AbstractWood from four types of casks used for the maturation of Scotch whisky was analysed for free vanillin, syringaldehyde, vanillic and syringic acids and for milled wood lignin. Degradation of wood lignin by acidolysis was used to estimate the proportion of intact β‐aryl ether linkages present. The yield of milled wood lignin was unaffected by repeated cask use. A comparison of acidolysis yields and the analysis of spirit matured for 3 years in each of the four types of cask indicated that the majority of β‐aryl ether linkages in oak lignin are resistant to spirit hydrolysis and that cask exhaustion was not accompanied by significant delignification. Significant reductions in the concentrations of free guaiacyl and syringyl compounds were recorded for used casks and proved the best indicator of cask exhaustion.

Factors affecting lignin degradation in lignocellulose by Phanerochaete chrysosporium

Cultural conditions affecting lignin degradation by Phanerochaete chrysosporium in various lignocellulosic materials were studied in comparison to an isolated lignin preparation. With shallow mycelial cultures, the degradation of lignin in wood proceeded more slowly in a 100% O2-atmosphere than in an air atmosphere, indicating that pure oxygen was toxic to the fungus. The organism was able to degrade lignin efficiently even under 30% CO2 and 10% O2 concentrations. Evolution of 14CO2 from labelled lignocellulosic materials was shown not to be representative of total lignin degradation. Addition of glucose to the culture did not affect lignin degradation measured by 14CO2 evolution, whereas lignin degradation measured by Klason lignin method stopped completely (poplar) or slowed considerably (straw). Due to partial depolymerization of lignin to soluble products, measuring only the evolution of 14CO2 results in an underestimation of the total amount of lignin bioaltered. The soluble products from all of the tested lignocellulosic materials and from the isolated lignin had an average molecular weight of about 1,000 and the products could be further fractionated by ion exchange chromatography. The relative amount of these products could be varied from 15 to 45% from the original lignin.

Poplar Lignin Decomposition by Gram-Negative Aerobic Bacteria

Eleven gram-negative aerobic bacteria (Pseudomonadaceae and Neisseriaceae) out of 122 soil isolates were selected for their ability to assimilate poplar dioxane lignin without a cosubstrate. Dioxane lignin and milled wood lignin degradation rates ranged between 20 and 40% of initial content after 7 days in mineral medium, as determined by a loss of absorbance at 280 nm; 10 strains could degrade in situ lignin, as evidenced by the decrease of the acetyl bromide lignin content of microtome wood sections. No degradation of wood polysaccharides was detected. Lignin biodegradation by Pseudomonas 106 was confirmed by CO(2) release from labeled poplar wood, although in lower yields compared with results obtained through chemical analysis based on acetyl bromide residual lignin determination.

Polysaccharide Integrity as Related to the Degradation of Lignin in Wood by White-Rot Fungi

Polysaccharide Integrity as Related to the Degradation of Lignin in Wood by White-Rot Fungi