Fungal biodegradation of lignopolystyrene graft copolymers.

White rot basidiomycetes were able to biodegrade styrene (1-phenylethene) graft copolymers of lignin containing different proportions of lignin and polystyrene [poly(1-phenylethylene)]. The biodegradation tests were run on lignin-styrene copolymerization products which contained 10.3, 32.2, and 50.4% (wt/wt) lignin. The polymer samples were incubated with the white rot fungi Pleurotus ostreatus, Phanerochaete chrysosporium, and Trametes versicolor and the brown rot fungus Gloeophyllum trabeum. White rot fungi degraded the plastic samples at a rate which increased with increasing lignin content in the copolymer sample. Both polystyrene and lignin components of the copolymer were readily degraded. Polystyrene pellets were not degradable in these tests. Degradation was verified for both incubated and control samples by weight loss, quantitative UV spectrophotometric analysis of both lignin and styrene residues, scanning electron microscopy of the plastic surface, and the presence of enzymes active in degradation during incubation. Brown rot fungus did not affect any of the plastics. White rot fungi produced and secreted oxidative enzymes associated with lignin degradation in liquid media during incubation with lignin-polystyrene copolymer.     

Fungal biodegradation of lignopolystyrene graft copolymers.

White rot basidiomycetes were able to biodegrade styrene (1-phenylethene) graft copolymers of lignin containing different proportions of lignin and polystyrene [poly(1-phenylethylene)]. The biodegradation tests were run on lignin-styrene copolymerization products which contained 10.3, 32.2, and 50.4% (wt/wt) lignin. The polymer samples were incubated with the white rot fungi Pleurotus ostreatus, Phanerochaete chrysosporium, and Trametes versicolor and the brown rot fungus Gloeophyllum trabeum. White rot fungi degraded the plastic samples at a rate which increased with increasing lignin content in the copolymer sample. Both polystyrene and lignin components of the copolymer were readily degraded. Polystyrene pellets were not degradable in these tests. Degradation was verified for both incubated and control samples by weight loss, quantitative UV spectrophotometric analysis of both lignin and styrene residues, scanning electron microscopy of the plastic surface, and the presence of enzymes active in degradation during incubation. Brown rot fungus did not affect any of the plastics. White rot fungi produced and secreted oxidative enzymes associated with lignin degradation in liquid media during incubation with lignin-polystyrene copolymer.     

Lignin degradation by white rot fungi on spruce wood shavings during short-time solid-state fermentations monitored by near infrared spectroscopy

Due to their outstanding capability of degrading the recalcitrant biomacromolecule lignin, white rot fungi have been attracting interest for several technological applications in mechanical pulping and wood surface modification. However, little is known about the time course of delignification in early stages of colonisation of wood by these fungi. Using a Fourier transform near infrared (FT-NIR) spectroscopic technique, lignin loss of sterilised spruce wood shavings (0.4–2.0 mm particle size) that had been degraded by various species of white rot fungi could be monitored already during the first 2 weeks. The delignification kinetics of Dichomitus squalens, three Phlebia species (Phlebia brevispora, Phlebia radiata and Phlebia tremellosa), three strains of Ceriporiopsis subvermispora as well as the white rot ascomycete Hypoxylon fragiforme and the basidiomycete Oxyporus latemarginatus were determined. Each of the fungi tested was able to reduce the lignin content of spruce wood significantly during the first week. The amount of delignification achieved by the selected white rot fungi after 2 weeks ranged from 7.2% for C. subvermispora (FPL 105.752) to 2.5% for P. radiata. Delignification was significant (P = 95%) already after 3 days treatment with C. subvermispora and P. tremellosa. Activities of extracellular ligninolytic enzymes (laccase, manganese peroxidase and/or lignin peroxidase), expressed by each of the tested fungi, were determined. Lignin was degraded when peroxidase activity was detected in the fungal cultures, but only a low level of correlation between enzyme activities and the extent of delignification was found.     

Synergy between pretreatment lignocellulose modifications and saccharification efficiency in two brown rot fungal systems

Brown rot wood-degrading fungi distinctly modify lignocellulose and completely hydrolyze polysaccharides (saccharification), typically without secreting an exo-acting glucanase and without removing lignin. Although each step of this two-step approach evolved within the same organism, it is unknown if the early lignocellulose modifications are made to specifically facilitate their own abbreviated enzyme system or if enhancements are more general. Because commercial pretreatments are typically approached as an isolated step, answering this question has immense implication on bioprocessing. We pretreated spruce and pine blocks with one of two brown rot fungi, Gloeophyllum trabeum or Fomitopsis pinicola. Wood harvested at weeks 1, 2, 4, and 8 showed a progression of weight loss from time zero due to selective carbohydrate removal. Hemicellulose losses progressed faster than cellulose loss. This “pretreated” material was then saccharified with commercially relevant Trichoderma reesei cellulases or with cellulases from the brown rot fungi responsible for degrading the wood to test for synergy. With increased decay, a significant increase in saccharification efficiency was apparent but not limited to same-species enzyme sources. We also calculated total sugar yields, and calculations that compensate for sugars consumed by fungi suggest a shorter residence time for fungal colonization than calculations based solely on saccharification yields.     

Wood-decay type and fungal guild dominance across a North American log transplant experiment

We incubated 196 large-diameter aspen (Populus tremuloides), birch (Betula papyrifera), and pine (Pinus taeda) logs on the FACE Wood Decomposition Experiment encompassing eight climatically-distinct forest sites in the United States. We sampled dead wood from these large-diameter logs after 2 to 6 y of decomposition and determined wood rot type as a continuous variable using the lignin loss/density loss ratio (L/D) and assessed wood-rotting fungal guilds using high-throughput amplicon sequencing (HTAS) of the ITS-2 marker. We found L/D values in line with a white rot dominance in all three tree species, with pine having lower L/D values than aspen and birch. Based on HTAS data, white rot fungi were the most abundant and diverse wood-rotting fungal guild, and soft rot fungi were more abundant and diverse than brown rot fungi in logs with low L/D values. For aspen and birch logs, decay type was related to the wood density at sampling. For the pine logs, decay type was associated with the balance between white and brown/soft rot fungi abundance and OTU richness. Our results demonstrate that decay type is governed by biotic and abiotic factors, which vary by tree species.     

Evaluation of the selectivity of white rot isolates using near infrared spectroscopic techniques

Seventeen isolates from white rotted beech wood and six strains from a local culture collection were evaluated for their capability to delignify beech and spruce wood selectively. Six peroxidase-positive isolates were found using a colorimetric agar plate test (Poly R-478), and genetically identified by their internal transcribed spacer (ITS1) or 28S rDNA sequences. Colonised on beech and spruce wood veneers, some of the peroxidase-positive isolates caused selective white rot on both wood species. Weight loss and lignin content of the degraded veneers were estimated from FT-NIR spectra with established linear regression models and multivariate models based on partial least squares regression (PLSR). Weight loss of the samples was also determined gravimetrically. A measure for the relative selectivity of the strains for lignin degradation was formulated and the values were calculated. Two strains that were identified as Oxyporus latemarginatus and Trametes cervina exhibited high selectivity on spruce wood, but the lignin content of the decayed wood was higher than that degraded by the reference strain Ceriporiopsis subvermispora. One strain – identified as Phlebia tremellosa – led to a lower lignin content of beech wood but caused also comparably high weight loss and thus exhibited an overall lower selectivity. The NIR spectroscopic method proved to be convenient for the quick screening of selective white rot fungi. Furthermore, the results revealed that high selectivity for lignin degradation is much more pronounced in early degradation stages.     

Degradation of endocrine disrupting chemicals by genetic transformants with two lignin degrading enzymes in <Emphasis Type="Italic">Phlebia tremellosa</Emphasis>

A white rot fungus Phlebia tremellosa produced lignin degrading enzymes, which showed degrading activity against various recalcitrant compounds. However, manganese peroxidase (MnP) activity, one of lignin degrading enzymes, was very low in this fungus under various culture conditions. An expression vector that carried both the laccase and MnP genes was constructed using laccase genomic DNA of P. tremellosa and MnP cDNA from Polyporus brumalis. P. tremellosa was genetically transformed using the expression vector to obtain fungal transformants showing increased laccase and MnP activity. Many transformants showed highly increased laccase and MnP activity at the same time in liquid medium, and three of them were used to degrade endocrine disrupting chemicals. The transformant not only degraded bisphenol A and nonylphenol more rapidly but also removed the estrogenic activities of the chemicals faster than the wild type strain.     

Lignin degradation by white rot fungi on spruce wood shavings during short-time solid-state fermentations monitored by near infrared spectroscopy

Due to their outstanding capability of degrading the recalcitrant biomacromolecule lignin, white rot fungi have been attracting interest for several technological applications in mechanical pulping and wood surface modification. However, little is known about the time course of delignification in early stages of colonisation of wood by these fungi. Using a Fourier transform near infrared (FT-NIR) spectroscopic technique, lignin loss of sterilised spruce wood shavings (0.4–2.0 mm particle size) that had been degraded by various species of white rot fungi could be monitored already during the first 2 weeks. The delignification kinetics of Dichomitus squalens, three Phlebia species (Phlebia brevispora, Phlebia radiata and Phlebia tremellosa), three strains of Ceriporiopsis subvermispora as well as the white rot ascomycete Hypoxylon fragiforme and the basidiomycete Oxyporus latemarginatus were determined. Each of the fungi tested was able to reduce the lignin content of spruce wood significantly during the first week. The amount of delignification achieved by the selected white rot fungi after 2 weeks ranged from 7.2% for C. subvermispora (FPL 105.752) to 2.5% for P. radiata. Delignification was significant (P = 95%) already after 3 days treatment with C. subvermispora and P. tremellosa. Activities of extracellular ligninolytic enzymes (laccase, manganese peroxidase and/or lignin peroxidase), expressed by each of the tested fungi, were determined. Lignin was degraded when peroxidase activity was detected in the fungal cultures, but only a low level of correlation between enzyme activities and the extent of delignification was found.     

Comparing lignocellulose physiochemistry after decomposition by brown rot fungi with distinct evolutionary origins

Among wood‐degrading fungi, lineages holding taxa that selectively metabolize carbohydrates without significant lignin removal (brown rot) are polyphyletic, having evolved multiple times from lignin‐removing white rot fungi. Given the qualitative nature of the ‘brown rot’ classifier, we aimed to quantify and compare the temporal sequence of carbohydrate removal among brown rot clades. Lignocellulose deconstruction was compared among fungi using distinct plant substrates (angiosperm, conifer, grass). Specifically, aspen, pine and corn stalk were harvested over a 16‐week time series from microcosms containing Gloeophyllum trabeum, Fomitopsis pinicola, Ossicaulis lignatilis, Fistulina hepatica, Serpula lacrymans, Wolfiporia cocos or Dacryopinax sp. After quantifying plant mass loss, a thorough compositional analysis was complemented by a saccharification test to determine wood cell wall accessibility. Mass loss and accessibility varied depending on fungal decomposer and substrate, and trajectories of loss for hemicellulosic components and cellulose differed among plant tissue types. At any given stage of decomposition, however, lignocellulose accessibility and the fraction remaining of carbohydrates and lignin within a plant tissue type were generally the same, regardless of fungal isolate. This suggests that the sequence of plant component removal at this typical scale of characterization is shared among these brown rot lineages, despite their diverse genomes and secretomes.     

Screening Wood Decayed by White Rot Fungi for Preferential Lignin Degradation

A screening procedure in which scanning electron microscopy was used indicated that 26 white rot fungi selectively removed lignin from various coniferous and hardwood tree species. Delignified wood from field collections had distinct micromorphological characteristics that were easily differentiated from other types of decay. The middle lamella was degraded, and the cells were separated from one another. Secondary cell wall layers that remained had a fibrillar appearance. Chemical analyses of delignified wood indicated that the cells were composed primarily of cellulose. Only small percentages of lignin and hemicellulose were evident. Delignified wood was not uniformly distributed throughout the decayed wood samples. White-pocket and white-mottled areas of the various decayed wood examined contained delignified cells, but adjacent wood had a nonselective removal of lignin where all cell wall components had been degraded simultaneously. This investigation demonstrates that selective delignification among white rot fungi is more prevalent than previously realized and identifies a large number of fungi for use in studies of preferential lignin degradation.     

Evaluation of the selectivity of white rot isolates using near infrared spectroscopic techniques

Seventeen isolates from white rotted beech wood and six strains from a local culture collection were evaluated for their capability to delignify beech and spruce wood selectively. Six peroxidase-positive isolates were found using a colorimetric agar plate test (Poly R-478), and genetically identified by their internal transcribed spacer (ITS1) or 28S rDNA sequences. Colonised on beech and spruce wood veneers, some of the peroxidase-positive isolates caused selective white rot on both wood species. Weight loss and lignin content of the degraded veneers were estimated from FT-NIR spectra with established linear regression models and multivariate models based on partial least squares regression (PLSR). Weight loss of the samples was also determined gravimetrically. A measure for the relative selectivity of the strains for lignin degradation was formulated and the values were calculated. Two strains that were identified as Oxyporus latemarginatus and Trametes cervina exhibited high selectivity on spruce wood, but the lignin content of the decayed wood was higher than that degraded by the reference strain Ceriporiopsis subvermispora. One strain – identified as Phlebia tremellosa – led to a lower lignin content of beech wood but caused also comparably high weight loss and thus exhibited an overall lower selectivity. The NIR spectroscopic method proved to be convenient for the quick screening of selective white rot fungi. Furthermore, the results revealed that high selectivity for lignin degradation is much more pronounced in early degradation stages.     

六种白腐菌预处理对毛白杨木材酶水解效果的影响

通过化学分析和酶水解试验,研究了不同的白腐菌对毛白杨的预处理效果及不同组分的降解对酶水解的影响。毛白杨木片经6种白腐菌预处理30d后,各组分都发生了降解,其中半纤维素的损失最为显著,Trametes ochracea C6888引起半纤维素降解率高达47.19%,其次是纤维素和酸不溶木素的降解。在后续酶水解过程中,6种白腐菌处理后的样品显示出不同的水解模式,菌株Trametes ochracea C6888、T. pubescens C7571和T. versicolor C6915预处理效果最为显著,还原糖得率在整个酶水解过程中一直高于对照,其中T. ochracea C6888在水解96h后还原糖得率达到15.93%,比未处理样品提高了25%。分析酸不溶木素降解率及半纤维素降解率与还原糖得率的关系发现,不同菌株在作用同一种基质时,预处理效果差异显著,木质素和半纤维素的脱除都会影响木质纤维素的酶水解。     

Comparison of methods to evaluate the potential of fungal growth on decay of spruce wood after short-time treatment

Several analytical methods were compared to evaluate characteristic wood decaying fungi for their potential to depolymerise lignin on spruce wood particles. Wood samples were treated with the white rot fungi Phlebia brevispora, Ceriporiopsis subvermispora, Merulius tremellosus, Pycnoporus sanguineus, Trametes pubescens and with the brown rot fungus Gloeophyllum trabeum. The UV absorbancies of crude ethanol extracts, total extractives content from sequential extraction, ligninolytic enzyme activities, lignin solubilisation and decrease of lignin content were compared. It was shown, that, in early decay stages, UV absorbancies of crude ethanol extracts and total extractives content correlate well with lignin degradation, increase of acid soluble lignin and increased production of ligninolytic enzymes (total peroxidase). Lignin content was determined using FT-NIR spectroscopy as well as by wet-chemical analysis, indicating a very good correlation between the two methods. According to the different analytical methods, the tested fungi can be classified into three categories based on their characteristic behaviour: brown rot, “slow” and “fast” white rot.     

Lignocellulosic polysaccharides and lignin degradation by wood decay fungi: the relevance of nonenzymatic Fenton-based reactions

The brown rot fungus Wolfiporia cocos and the selective white rot fungus Perenniporia medulla-panis produce peptides and phenolate-derivative compounds as low molecular weight Fe³⁺-reductants. Phenolates were the major compounds with Fe³⁺-reducing activity in both fungi and displayed Fe³⁺-reducing activity at pH 2.0 and 4.5 in the absence and presence of oxalic acid. The chemical structures of these compounds were identified. Together with Fe³⁺ and H₂O₂ (mediated Fenton reaction) they produced oxygen radicals that oxidized lignocellulosic polysaccharides and lignin extensively in vitro under conditions similar to those found in vivo. These results indicate that, in addition to the extensively studied Gloeophyllum trabeum—a model brown rot fungus—other brown rot fungi as well as selective white rot fungi, possess the means to promote Fenton chemistry to degrade cellulose and hemicellulose, and to modify lignin. Moreover, new information is provided, particularly regarding how lignin is attacked, and either repolymerized or solubilized depending on the type of fungal attack, and suggests a new pathway for selective white rot degradation of wood. The importance of Fenton reactions mediated by phenolates operating separately or synergistically with carbohydrate-degrading enzymes in brown rot fungi, and lignin-modifying enzymes in white rot fungi is discussed. This research improves our understanding of natural processes in carbon cycling in the environment, which may enable the exploration of novel methods for bioconversion of lignocellulose in the production of biofuels or polymers, in addition to the development of new and better ways to protect wood from degradation by microorganisms.     

Lignin-modifying enzymes of the white rot basidiomycete Ganoderma lucidum

Ganoderma lucidum, a white rot basidiomycete widely distributed worldwide, was studied for the production of the lignin-modifying enzymes laccase, manganese-dependent peroxidase (MnP), and lignin peroxidase (LiP). Laccase levels observed in high-nitrogen (HN; 24 mM N) shaken cultures were much greater than those seen in low-nitrogen (2.4 mM N), malt extract, or wood-grown cultures and those reported for most other white rot fungi to date. Laccase production was readily seen in cultures grown with pine or poplar (100-mesh-size ground wood) as the sole carbon and energy source. Cultures containing both pine and poplar showed 5- to 10-fold-higher levels of laccase than cultures containing pine or poplar alone. Since syringyl units are structural components important in poplar lignin and other hardwoods but much less so in pine lignin and other softwoods, pine cultures were supplemented with syringic acid, and this resulted in laccase levels comparable to those seen in pine-plus-poplar cultures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of concentrated extracellular culture fluid from HN cultures showed two laccase activity bands (M(r) of 40,000 and 66, 000), whereas isoelectric focusing revealed five major laccase activity bands with estimated pIs of 3.0, 4.25, 4.5, 4.8, and 5.1. Low levels of MnP activity ( approximately 100 U/liter) were detected in poplar-grown cultures but not in cultures grown with pine, with pine plus syringic acid, or in HN medium. No LiP activity was seen in any of the media tested; however, probing the genomic DNA with the LiP cDNA (CLG4) from the white rot fungus Phanerochaete chrysosporium showed distinct hybridization bands suggesting the presence of lip-like sequences in G. lucidum.     

Fungal resistance of rubber wood modified by fatty acid chlorides

Decay resistance of Rubber wood (Hevea brasiliensis) esterified with three fatty acid chlorides (hexanoyl chloride (C6), decanoyl chloride (C10) and tetra-decanoyl chloride (C14)) was evaluated. Unmodified and modified wood samples were exposed to a brown rot (Polyporus meliae) and a white rot (Coriolus versicolor) fungus for 12 weeks. Unmodified rubber wood was severely decayed by P. meliae and C. versicolor, which was indicated by significant weight loss. The rate of decay by brown rot was higher than white rot. Modified wood samples exhibited very good resistant to brown and white-rot fungi. The degree of protection increased with increase in degree of modification. P. meliae, a brown rot fungus, removed structural carbohydrate component in unmodified wood selectively whereas, C. vesicolor showed preference to lignin. The FTIR spectra of modified wood exposed to fungi show no significant changes in relative peak intensities of lignin/carbohydrates indicating effectiveness of chemically modified wood in restricting chemical degradation. Chemical modification occurred more efficiently at carbohydrate portion of the wood. Therefore, it is more effective in retarding decay due to P. meliae.     

Progressive changes in cell wall components of Pinus radiata during decay

Progressive changes in solubility characteristics and lignin content of Pinus radiata sapwood were assessed when small blocks were subjected to decay by brown (Gloeophyllum trabeum) and white (Perenniporia tephropora) rot fungi. The brown rot species removed lignin in approximate proportion to weight loss up to 10%; thereafter the amount of lignin altered little. In contrast, the decline in lignin content was near linear for P. tephropora. Increases in solubility (particularly with hot water and dilute alkali), in sugar content and in the acidity of aqueous extracts were recorded in wood blocks decayed to 15–20% weight loss. While these effects were more pronounced in samples decayed by G. trabeum, it appears that with both organisms structural components were degraded faster than the products could be utilised. In this case, cell wall chemistry may not have been a major determinant of weight losses.     

Methane fermentation of Japanese cedar wood pretreated with a white rot fungus, Ceriporiopsis subvermispora

Methane fermentation of Japanese cedar wood was carried out after pretreatment with four strains of white rot fungi, Ceriporiopsis subvermispora ATCC 90467, CZ-3, CBS 347.63 and Pleurocybella porrigens K-2855. These fungi were cultivated on wood chip media with and without wheat bran for 4-8 weeks. The pretreated wood chip was fermented anaerobically with sludge from a sewage treatment plant. Pretreatments with C. subvermispora ATCC 90467, CZ-3 and CBS 347.63 in the presence of wheat bran for 8 weeks decreased 74-76% of beta-O-4 aryl ether linkages in the lignin to accelerate production of methane. After fungal treatments with C. subvermispora ATCC 90467 and subsequent 30-days methane fermentation, the methane yield reached 35 and 25% of the theoretical yield based on the holocellulose contents of the decayed and original wood, respectively. In contrast, treatment with the three strains of C. subvermispora without wheat bran cleaved 15-26% of the linkage and produced 6-9% of methane. There were no significant accelerating effects in wood chips treated with P. porrigens which has a lower ability to decompose the lignin. Thus, it was found that C. subvermispora, with a high ability to decompose aryl ether bonds of lignin, promoted methane fermentation of softwood in the presence of wheat bran.     

Lignin-Modifying Enzymes of the White Rot Basidiomycete Ganoderma lucidum

Ganoderma lucidum, a white rot basidiomycete widely distributed worldwide, was studied for the production of the lignin-modifying enzymes laccase, manganese-dependent peroxidase (MnP), and lignin peroxidase (LiP). Laccase levels observed in high-nitrogen (HN; 24 mM N) shaken cultures were much greater than those seen in low-nitrogen (2.4 mM N), malt extract, or wood-grown cultures and those reported for most other white rot fungi to date. Laccase production was readily seen in cultures grown with pine or poplar (100-mesh-size ground wood) as the sole carbon and energy source. Cultures containing both pine and poplar showed 5- to 10-fold-higher levels of laccase than cultures containing pine or poplar alone. Since syringyl units are structural components important in poplar lignin and other hardwoods but much less so in pine lignin and other softwoods, pine cultures were supplemented with syringic acid, and this resulted in laccase levels comparable to those seen in pine-plus-poplar cultures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of concentrated extracellular culture fluid from HN cultures showed two laccase activity bands (M_r of 40,000 and 66,000), whereas isoelectric focusing revealed five major laccase activity bands with estimated pIs of 3.0, 4.25, 4.5, 4.8, and 5.1. Low levels of MnP activity (~100 U/liter) were detected in poplar-grown cultures but not in cultures grown with pine, with pine plus syringic acid, or in HN medium. No LiP activity was seen in any of the media tested; however, probing the genomic DNA with the LiP cDNA (CLG4) from the white rot fungus Phanerochaete chrysosporium showed distinct hybridization bands suggesting the presence of lip-like sequences in G. lucidum.     

Diversity and decay ability of basidiomycetes isolated from lodgepole pines killed by the mountain pine beetle

When lodgepole pines (Pinus contorta Douglas ex Louden var. latifolia Engelm. ex S. Watson) that are killed by the mountain pine beetle (Dendroctonus ponderosae) and its fungal associates are not harvested, fungal decay can affect wood and fibre properties. Ophiostomatoids stain sapwood but do not affect the structural properties of wood. In contrast, white or brown decay basidiomycetes degrade wood. We isolated both staining and decay fungi from 300 lodgepole pine trees killed by mountain pine beetle at green, red, and grey stages at 10 sites across British Columbia. We retained 224 basidiomycete isolates that we classified into 34 species using morphological and physiological characteristics and rDNA large subunit sequences. The number of basidiomycete species varied from 4 to 14 species per site. We assessed the ability of these fungi to degrade both pine sapwood and heartwood using the soil jar decay test. The highest wood mass losses for both sapwood and heartwood were measured for the brown rot species Fomitopsis pinicola and the white rot Metulodontia and Ganoderma species. The sap rot species Trichaptum abietinum was more damaging for sapwood than for heartwood. A number of species caused more than 50% wood mass losses after 12 weeks at room temperature, suggesting that beetle-killed trees can rapidly lose market value due to degradation of wood structural components.