Wood Decay by Brown-Rot Fungi: Changes in Pore Structure and Cell Wall Volume

Flournoy, Douglas S.; Kirk, T. Kent; Highley, Terry L.

doi:10.1515/hfsg.1991.45.5.383

Cited by 170 publications

(94 citation statements)

References 10 publications

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“…In distal sections of the P. placenta mycelium, the delayed and marked up-regulation of CAZys, specifically GHs, implies that cellulases and hemicellulases have a significant role in wood decay, contrary to the classical view that these enzymes cannot infiltrate the wood cell wall during brown rot (40). These CAZys include not only several previously characterized endoglucanases (29) but also numerous hemicellulases and carbohydrate esterases, many of which remain poorly characterized (e.g., feruloyl esterases, GH53 arabinogalactan endo-β-galactosidase).…”

Section: Discussionmentioning

confidence: 82%

Localizing gene regulation reveals a staggered wood decay mechanism for the brown rot fungus Postia placenta

Zhang

Presley

Hammel

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

168

214

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Wood-degrading brown rot fungi are essential recyclers of plant biomass in forest ecosystems. Their efficient cellulolytic systems, which have potential biotechnological applications, apparently depend on a combination of two mechanisms: lignocellulose oxidation (LOX) by reactive oxygen species (ROS) and polysaccharide hydrolysis by a limited set of glycoside hydrolases (GHs). Given that ROS are strongly oxidizing and nonselective, these two steps are likely segregated. A common hypothesis has been that brown rot fungi use a concentration gradient of chelated metal ions to confine ROS generation inside wood cell walls before enzymes can infiltrate. We examined an alternative: that LOX components involved in ROS production are differentially expressed by brown rot fungi ahead of GH components. We used spatial mapping to resolve a temporal sequence in Postia placenta, sectioning thin wood wafers colonized directionally. Among sections, we measured gene expression by whole-transcriptome shotgun sequencing (RNA-seq) and assayed relevant enzyme activities. We found a marked pattern of LOX up-regulation in a narrow (5-mm, 48-h) zone at the hyphal front, which included many genes likely involved in ROS generation. Up-regulation of GH5 endoglucanases and many other GHs clearly occurred later, behind the hyphal front, with the notable exceptions of two likely expansins and a GH28 pectinase. Our results support a staggered mechanism for brown rot that is controlled by differential expression rather than microenvironmental gradients. This mechanism likely results in an oxidative pretreatment of lignocellulose, possibly facilitated by expansin-and pectinase-assisted cell wall swelling, before cellulases and hemicellulases are deployed for polysaccharide depolymerization.B rown rot wood-degrading fungi release sequestered carbon from lignocellulose in forests (1) and have the unique ability to accomplish this without significantly removing the recalcitrant lignin that encases the structural polysaccharides. Accordingly, their decay mechanisms may provide a model for new biomass conversion technologies that not only function despite the presence of lignin but also yield lignin as a potentially useful coproduct (1-3). Deviating from their white rot ancestors, brown rot fungi have evolved mechanisms that are generally faster (4, 5) and more polysaccharide-specific because they circumvent lignin (4,(6)(7)(8). This enhanced efficiency is coupled with losses, not expansions, of key white rot genes, including many linked to lignin degradation and processive cellulose hydrolysis. For example, few brown rot fungi produce the cellobiohydrolases that are included in commercial synergistic glycoside hydrolase (GH) mixtures (9-12). These observations imply that brown rot fungi harbor novel pathways to improve saccharification yields.To explain why brown rot fungi are so efficient, despite their minimal toolkit of biodegradative enzymes, low-molecular-weight (LMW) oxidative agents have been proposed to operate in tandem with the enzymes. ...

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Section: Discussionmentioning

confidence: 82%

Localizing gene regulation reveals a staggered wood decay mechanism for the brown rot fungus Postia placenta

Zhang

Presley

Hammel

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

168

214

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“…The method was originally developed by Aggebrandt and Samuelson (1964) and modified by Stone and co-workers (Stone et al 1969;Scallan 1967, 1968a, b) to characterise pore volumes and pore size distributions in pulps in the water-swollen state. Since then, SET has been used to characterise both untreated (Ahlgren et al 1972;Farahani 2003;Feist and Tarkow 1967;Flournoy et al 1991Flournoy et al , 1993Forster 1998) and modified wood (Farahani 2003;Forster 1998). In SET, a water-saturated sample with known mass of water is placed in an aqueous solution of molecular probe solutes of a known size and concentration.…”

Section: Solute Exclusion Techniquementioning

confidence: 99%

“…In SET, a water-saturated sample with known mass of water is placed in an aqueous solution of molecular probe solutes of a known size and concentration. The typical sample is a cuboid of 20-30 mm side length and a thickness of 3-5 mm (Farahani 2003;Flournoy et al 1991Flournoy et al , 1993Forster 1998), although several older studies have used shavings, pulp, or milled wood (Ahlgren et al 1972;Feist and Tarkow 1967;Stone and Scallan 1968b). As solutes diffuse into the water within the sample, their concentration in the surrounding solution decreases.…”

Section: Solute Exclusion Techniquementioning

confidence: 99%

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

2017

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Water plays a central role in wood research, since it affects all material properties relevant to the performance of wood materials. Therefore, experimental techniques for characterising water within wood are an essential part of nearly all scientific investigations of wood materials. This review focuses on selected experimental techniques that can give deeper insights into various aspects of water in wood in the entire moisture domain from dry to fully water-saturated. These techniques fall into three broad categories: (1) gravimetric techniques that determine how much water is absorbed, (2) fibre saturation techniques that determine the amount of water within cell walls, and (3) spectroscopic techniques that provide insights into chemical wood-water interactions as well as yield information on water distribution in the macro-void wood structure. For all techniques, the general measurement concept is explained, its history in wood science as well as advantages and limitations.

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“…The initial fungal decay of wood cannot be exclusively induced by enzymes because these are not able to penetrate the cell wall. The diameters of cell wall micropores above the fibre saturation point (FSP) do not exceed 2 nm, while the hydrodymamic diameters of enzymes such as peroxidises, laccases, cellulases, or xylanases are not smaller than 4 nm (Flournoy et al 1991). Brown rot fungi are the only species that are able to degrade cellulose and hemicelluloses without prior removal of lignin.…”

Section: Introductionmentioning

confidence: 99%

“…Brown rot fungi are the only species that are able to degrade cellulose and hemicelluloses without prior removal of lignin. It was demonstrated that white rot decay led to a much higher increase in the cell wall pore diameter than brown rot decay did at the same mass loss (ML) level (Flournoy et al 1991(Flournoy et al , 1993. This specific decay pattern and the absence of exo-β-glucanases in several brown rot fungi (Highley and Dashek 1998) led to the conclusion that diffusion of low molecular weight (MW low ) agents might cause oxidative degradation of polysaccharides, resulting in strength loss prior to ML (Green et al 1991;Winandy and Morrell 1993;Green and Highley 1997).…”

Section: Introductionmentioning

confidence: 99%

Degradation of chemically modified Scots pine (Pinus sylvestris L.) with Fenton reagent

Xie¹,

Xiao²,

Mai

2014

Holzforschung

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Abstract:The Fenton reaction is supposed to play a key role in the initial wood degradation by brown rot fungi. Wood was modified with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and glutaraldehyde (GA) to various weight percentage gains in order to study if these types of modifications are able to reduce wood degradation by Fenton reagent. Veneers modified with higher concentrations (1.2 and 2.0 mol l -1 ) of both chemicals exhibited minor losses in mass and tensile strength during treatment with Fenton reagent, which shows restrained oxidative degradation by hydroxyl radicals. The decomposition rate of H 2 O 2 was lower in the Fenton solutions containing modified veneers than in those containing unmodified controls. More CO 2 evolved in systems containing unmodified veneers than in systems with modified veneers, indicating that modification protected wood from mineralisation. The reason for the enhanced resistance of modified wood to the Fenton reaction is attributed to impeded diffusion of the reagent into the cell wall rather than to inhibition of the Fenton reaction itself. The results show that wood modification with DMDHEU and GA is able to restrain the degradation of wood by the Fenton reaction and can explain why modified wood is more resistant to brown rot decay.

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Wood Decay by Brown-Rot Fungi: Changes in Pore Structure and Cell Wall Volume

Cited by 170 publications

References 10 publications

Localizing gene regulation reveals a staggered wood decay mechanism for the brown rot fungus Postia placenta

Localizing gene regulation reveals a staggered wood decay mechanism for the brown rot fungus Postia placenta

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

Degradation of chemically modified Scots pine (Pinus sylvestris L.) with Fenton reagent

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