Fungal decay resistance and durability of organosilicon-treated wood

The potential use of organosilicons as protective agents against basidiomycetes attack of wood used in outdoor applications was investigated using Scots pine sapwood and beech specimens. Both mini-blocks and EN 113 specimens were subjected to brown-rot and white-rot fungi. A dose–response could be observed showing that with higher weight percentage gain of the organosilicon, the resistance (i.e., efficacy) against fungi increased. At relatively low weight percentage gains, which are assumed to be economically feasible, Scots pine could be partly protected against decay by Postia placenta and Coniophora puteana and beech could be partly protected against decay by C. puteana and Trametes versicolor. Full protection was achieved by some silicons for Scots pine sapwood against C. puteana and for beech against T. versicolor. The most promising products were a solvent-based mixture of the alkoxysilanes methyltrimethoxysilane (MTM) and octyltriethoxysilane (OTES) and a water-based micro-emulsion of polydimethylsiloxane (PDMS) and triethoxysilane (TES) when applied above 20 and 30% weight gain for Scots pine and above 30 and 40% weight gain for beech. A water-based mixture of dimethylmethylhydrogen siloxane (DMS) and N-octyltriethoxysilane (n-OTES) was able to protect beech at weight gains above 30%.     

Immunological characterization of lignocellulose degradation

Polyclonal antibodies produced to the brown-rot fungus Poria placenta have been used with fluorescence microscopy to detect fungal hyphae colonizing wood. In addition, an enzyme-linked immunosorbent assay (ELISA) has been used to detect and quantify the extent of fungal decay in wood. ELISA values correlated with percent weight loss associated with fungal degradation and the assay was able to detect fungal colonization ten days after inoculation in solid wood. Monoclonal antibodies to extracellular metabolites of P. placenta have been produced and are being characterized. Monoclonal antibodies have also been produced to native and partially deglycosylated Mn2 peroxidase. The use of immunological probes to monitor and characterize the decay process is discussed.     

Cellulose Degradation by Cellulose-Clearing and Non-Cellulose-Clearing Brown-Rot Fungi

Cellulose degradation by four cellulose-clearing brown-rot fungi in the Coniophoraceae—Coniophora prasinoides, C. puteana, Leucogyrophana arizonica, and L. olivascens—is compared with that of a non-cellulose-clearing brown-rot fungus, Poria placenta. The cellulose- and the non-cellulose-clearing brown-rot fungi apparently employ similar mechanisms to depolymerize cellulose; most likely a nonenzymatic mechanism is involved.     

Study of the structure of biodegraded wood using the water vapour sorption method

The dynamics of the biodegradation of wood by brown-rot fungi (Coniophora puteana, Poria placenta, and Gloephyllum trabeum) was investigated by the water vapour sorption method. The change in wood microstructure characteristics (specific surface and concentration of surface hydrophilic centres) with increasing exposure time correlated with reduction in mass and change in composition. Two-to-eight-nanometer-wide micropores, whose size and volume depended on the fungal species and exposure time, appeared in the wood. Methodological aspects of the application of sorption methods should be taken into account in the interpretation of the results.     

Degradation of extractive-free lignocelluloses by Coriolus versicolor and Poria placenta

Summary The wood-decay fungi Coriolus versicolor, a white-rot fungus, and Poria placenta, a brown-rot fungus, were grown on an extractive-free lignocellulose prepared from quackgrass (Agropyron repens). Their abilities to decompose this lignocellulose were compared to their abilities to decompose softwood (Picea pungens) and hardwood (Acer rubrum) lignocelluloses. The two fungi were grown on malt-extract dampened lignocelluloses at 28°C for up to 12 weeks. Replicate cultures were periodically harvested and lignocellulose decomposition was followed by monitoring substrate weight loss, lignin loss, and carbohydrate loss. Coriolus versicolor decomposed the lignin and carbohydrate components of the grass lignocellulose as efficiently as the softwood and hardwood lignocelluloses. Poria placenta, however, was not an efficient degrader of either lignin or carbohydrate in the grass lignocellulose. Poria placenta readily decomposed carbohydrate components of the softwood lignocellulose but not the hardwood lignocellulose.Paper number 81520 of the Idaho Agricultural Experiment Station     

Decay and termite resistance of medium density fiberboard (MDF) made from different wood species

Medium density fiberboard (MDF) production worldwide is increasing due to the development of new manufacturing technologies. As a result, MDF products are increasingly utilized in traditional wood applications that require fungal and insect resistance. This study evaluated the ability of white and brown rot fungi and termites to decompose MDF consisting of different wood species by measuring weight loss. Furnish in the boards was prepared from heart and sapwood portions of pine (Pinus nigra Arnold var. pallasiana), beech (Fagus orientalis Lipsky), and European oak (Quercus robur L.) species. Fungal decay resistance tests were performed according to ASTM D 2017-81 standard method using two brown-rot fungi, Gloeophyllum trabeum (Pers. ex Fr.) Murr. (Mad 617), Postia placenta (Fries) M. Larsen et Lombard (Mad 698), and one white-rot fungus, Trametes versicolor (L. ex Ft.) Pilat (Mad 697). MDF and wood specimens were also bioassayed against the eastern subterranean termite, Reticulitermes flavipes (Kollar) in order to determine termite resistance of the specimens. MDF specimens containing oak and mixed furnish demonstrated increased durability against decay fungi. Only pine, oak, and mixed MDF specimens met the 25% or less weight loss limit to be classified resistant according to ASTM D 2017-81 standard method. Overall, MDF specimens made from oak showed better performance than oak solid wood specimens. Accelerated aging according to ASTM D 1037-96a standard method before fungal bioassay decreased fungal resistance of the specimens. In contrast to the fungal bioassay, MDF specimens made from beech and mixed furnish showed decreased weight losses from termite attack after 4 weeks. However, none of the MDF specimens were resistant to termite attack. In severe conditions, the MDFs may require the incorporation of chemical biocides prior to board production for increasing the resistance of MDF to termite attack.     

Temporal changes in wood crystalline cellulose during degradation by brown rot fungi

The degradation of wood by brown rot fungi has been studied intensely for many years in order to facilitate the preservation of in-service wood. In this work we used X-ray diffraction to examine changes in wood cellulose crystallinity caused by the brown rot fungi Gloeophyllum trabeum, Coniophora puteana, and two isolates of Serpula lacrymans. All fungi increased apparent percent crystallinity early in the decay process while decreasing total amounts of both crystalline and amorphous material. Data also showed an apparent decrease of approximately 0.05 Å in the average spacing of the crystal planes in all degraded samples after roughly 20% weight loss, as well as a decrease in the average observed relative peak width at 2θ = 22.2°. These results may indicate a disruption of the outer most semi-crystalline cellulose chains comprising the wood microfibril. X-ray diffraction analysis of wood subjected to biological attack by fungi may provide insight into degradative processes and wood cellulose structure.     

Comparative natural durability of five wood species from Mozambique

The objective of this study was to evaluate the natural durability of five lesser-utilized wood species from Mozambique. Both laboratory methods and field tests were applied for assessing wood decay of muanga (Pericopsis angolensis), metil (Sterculia appendiculata), namuno (Acacia nigrescens), ncurri (Icuria dunensis), and ntholo (Pseudolachnostylis maprounaefolia). Laboratory tests involved soft-, brown-, and white-rot fungi and termites. Heart- and sapwood of ncurri and ntholo were exposed in above-ground field tests; additionally, all species were exposed to in-ground contact tests. The results indicated that namuno, muanga, ncurri, and ntholo are resistant to soft-, brown- and white-rot fungi and the termite species Reticulitermes grassea and Mastotermes darwiniensis. Comparatively, soft-rot caused more severe decay on the studied wood species than did basidiomycete fungi. The brown-rot fungi Coniophora puteana, Gloeophiyllum trabeum, and Postia placenta caused less decay on the tested species than did the white-rot Trametes versicolor. Metil was not resistant to any of the mentioned hazards. Therefore, this species is not recommendable for exterior use if untreated.     

Fungal bioleaching of metals in preservative-treated wood

Twenty-four brown-rot and 10 white-rot fungi were screened to evaluate their applicability for detoxification of preservative-treated wood impregnated with copper and chromium (CC) salts. Brown-rot fungi generally showed higher tolerance towards copper inhibition than white-rot fungi. Additionally, brown-rot fungi were found to accumulate considerable quantities of oxalic acid (up to 44.3 mM) in liquid medium, while white-rot fungi generally accumulated only traces of this organic acid. Oxalic acid is a strong organic acid capable of complexing a variety of heavy metals. Four Antrodia vaillantii and two Poria placenta brown-rot strains that displayed both a high copper tolerance and a high oxalic acid production were selected for further study. The brown-rot fungi effectively decayed wood containing up to 4.4% CC causing corrected mass losses of up to 24.3% in 4 weeks. Fungal treatment was also found to promote extensive leaching of chromium (up to 52.4%), but only moderate leaching of copper (15.6% or less). These results indicate the potential of solid-state fermentation with copper-tolerant fungi for the remediation of preservative-treated wood. Improving the solubility of copper will be an important challenge for future research.     

Characterization of main sulfur source of wood-degrading basidiomycetes by S K-edge X-ray absorption near edge spectroscopy (XANES)

The main wood degraders in aerobic terrestrial ecosystems belong to the white- and brown-rot fungi, where their biomass can be created on wood decay only. However, total sulfur (S) concentration in wood is very low and only little is known about the different sulfur compounds in wood today. Sulfur-starved brown-rot fungi Gloeophyllum trabeum and Oligoporus placenta were incubated on sterilized pine wood blocks whereas Lentinus cyathiformis and the white-rot fungi Trametes versicolor were incubated on sterilized beech wood blocks. After 19 weeks of incubation, the S oxidation status was analyzed in wood, in degraded wood, and in biomass of wood-degrading fungi by synchrotron based S K-edge XANES, and total S and sulfate were quantified. Total sulfur and sulfate content in pine wood blocks were approximately 50 and 1 ??g g⁻¹, respectively, while in beech wood approximately 100 and 20 ??g g⁻¹ were found, respectively. Sulfur in beech was dominated by sulfate-esters. In contrast, pine wood also contained larger amounts of reduced S. Three out of four selected fungi caused a reduction of the S oxidation state in wood from oxidized S (sulfate-ester, sulfate) to intermediate S (sulfonate, sulfoxide) or reduced S (thiols, e.g., proteins, peptides, enzyme cofactors). Only O. placenta shifted thiol to sulfonate. Growth experiments of these fungi on selective minimal media showed that in particular cysteine (thiol), sulfonates, and sulfate enhanced total mycelium growth. Consequently, wood-degrading fungi were able to utilize a large variety of different wood S sources for growth but preferentially transformed in vivo sulfate-esters and thiol into biomass structures.     

Blockboard with boron-treated veneers: laboratory decay and termite resistance tests

This study is evaluated by measuring the weight loss, and the ability of white- and brown-rot fungi and termites to attack untreated and boron-treated blockboard manufactured using untreated fir (Abies bornmulleriana M.) strips sandwiched between Ekaba (Tetraberlinia bifoliolata Harms.) veneers at final assembly. The veneers were treated with either boric acid or disodium octoborate tetrahydrate, or mixtures of these chemicals, and blockboard specimens were subjected to fungal decay resistance tests performed according to the Japanese Industrial Standard (JIS) A-9201 method using the brown-rot fungus Fomitopsis palustris (Berkeley et Curtis) Murrill and the white-rot fungus, Trametes versicolor (L. ex Fr.) Quel. Blockboard specimens were also tested against the subterranean termite Coptotermes formosanus Shiraki to determine termite resistance. Blockboard specimens with boron-treated veneers demonstrated increased durability against decay fungi and termite attack. However, sealing of untreated fir strips before decay resistance tests helped reduce significantly the weight losses in blockboard with either untreated or boron-treated veneers. Although blockboard is usually used in indoor applications, incorporation of boron-based biocides may be required for increasing resistance to fungal decay and termite attack and giving fire retardancy.     

Localisation and characterisation of incipient brown-rot decay within spruce wood cell walls using FT-IR imaging microscopy

Spruce wood that had been degraded by brown-rot fungi (Gloeophyllum trabeum or Poria placenta) exhibiting mass losses up to 16% was investigated by transmission Fourier transform infrared (FT-IR) imaging microscopy. Here the first work on the application of FT-IR imaging microscopy and multivariate image analysis of fungal degraded wood is presented and the first report on the spatial distribution of polysaccharide degradation during incipient brown-rot of wood. Brown-rot starts to become significant in the outer cell wall regions (middle lamellae, primary cell walls, and the outer layer of the secondary cell wall S1). This pattern was detected even in a sample with non-detectable mass loss. Most significant during incipient decay was the cleavage of glycosidic bonds, i.e. depolymerisation of wood polysaccharides and the degradation of pectic substances. Accordingly, intramolecular hydrogen bonding within cellulose was reduced, while the presence of phenolic groups increased.     

Selection of white-rot fungi for biopulping

Different rates of wood decay and ligninolytic activity were found in wood decayed by various white-rot fungi. Chemical and ultrastructural analyses showed wood decayed by Coriolus versicolor consisted of a nonselective attack on all cell wall components. Lignin degradation was restricted to the cell wall adjacent to hyphae or around the circumference of cell lumina. Decay by Phellinus pini, Phlebia tremellosus, Poria medullapanis and Scytinostroma galactinum was selective for lignin degradation. Secondary walls were void of lignin and middle lamellae were extensively degraded. A diffuse attack on lignin occurred throughout all cell wall layers. Variation in ligninolytic activity was found among strains of Phanerochaete chrysosporium. Differences in weight loss as well as lignin and polysaccharide degradation were also found when wood of different coniferous and deciduous tree species was decayed by various white-rot fungi.     

Evaluation of possible decay and termite resistance of particleboard containing waste tire rubber

Particleboard specimens produced by adding waste tire rubber particles were assayed against white- and brown-rot fungi and termites in laboratory conditions. Particleboards were manufactured from a mixture of pine and poplar particles bonded with two different resins (melamine/urea formaldehyde [MUF] and polyisocyanate [PI]) by adding waste tire rubber particles at three different levels (10%/90%, 20%/80%, and 30%/70% by weight of waste tire rubber/wood). The particleboard specimens with waste tire rubber were not generally resistant against four fungi tested. Only MUF-containing specimens showed considerably better performance in decay resistance tests using the brown-rot fungus, Postia placenta; however, addition of waste tire rubber into those specimens did not provide resistance in comparison with control specimens without tire rubber. Formosan termites were also able to degrade particleboard specimens with waste tire rubber.     

Fungal accumulation of metals from building materials during brown rot wood decay

This study analyzes the accumulation and translocation of metal ions in wood during the degradation performed by one strain of each of the three brown rot fungi; Serpula lacrymans, Meruliporia incrassata and Coniophora puteana. These fungi species are inhabitants of the built environment where the prevention and understanding of fungal decay is of high priority. This study focuses on the influence of various building materials in relation to fungal growth and metal uptake. Changes in the concentration of iron, manganese, calcium and copper ions in the decayed wood were analyzed by induced coupled plasma spectroscopy and related to wood weight loss and oxalic acid accumulation. Metal transport into the fungal inoculated wood was found to be dependent on the individual strain/species. The S. lacrymans strain caused a significant increase in total iron whereas the concentration of copper ions in the wood appeared decreased after 10 weeks of decay. Wood inoculated with the M. incrassata isolate showed the contrary tendency with high copper accumulation and low iron increase despite similar weight losses for the two strains. However, significantly lower oxalic acid accumulation was recorded in M. incrassata degraded wood. The addition of a building material resulted in increased weight loss in wood degraded by C. puteana in the soil-block test; however, this could not be directly linked specifically to the accumulation of any of the four metals recorded. The accumulation of oxalic acid seemed to influence the iron uptake. The study assessing the influence of the presence of soil and glass in the soil-block test revealed that soil contributed the majority of the metals for uptake by the fungi and contributed to increased weight loss. The varying uptake observed among the three brown rot fungi strains toward the four metals analyzed may be related to the specific non-enzymatic and enzymatic properties including bio-chelators employed by each of the species during wood decay.     

Metabolic activities and ultrastructure imaging at late-stage of wood decomposition in interactive brown rot - white rot fungal combinations

Basidiomycota brown rot fungus (Fomitopsis pinicola) and two white rot fungi (Phlebia radiata, Trichaptum abietinum) were cultivated on thin slices of spruce wood individually and in interspecies combinations. Within 12 months, F. pinicola substantially decomposed spruce wood observed as mass loss, also in three-species combinations. However, white rot fungi through hyphal interactions negatively affected the brown-rot indicative iron reduction capacity of F. pinicola. Decay-signature gene expression in mycelial interaction zones indicated suppression of brown rot mechanism but stimulation of enzymatic white-rot lignin attack by P. radiata. Wood ultrastructure imaging showed white-rot dominance in the fungal combinations, whereas destructive brown-rot was evident with F. pinicola alone. Our results confirm the dynamic pattern of enzyme production in fungal combinations, and transition from brown to white rot decomposition metabolism during the late stage of wood decay after one year of interspecific interactions.     

Heartwood extractives and lignin content of different larch species (<Emphasis Type="Italic">Larix </Emphasis>sp.) and relationships to brown-rot decay-resistance

The extractive content of lignin and the brown-rot decay-resistance against Coniophora puteana and Poria placenta were studied in larch heartwood from different species and origin (Larix decidua var. decidua, L. decidua var. sudetica, L. kaempferi , L. × eurolepis). The study material consisted of 106 trees from a 39-year old provenance trial in France. The hot-water-soluble extractives were very variable (from5.66% to 20.50% of dry weight), but there was no significant variation between the investigated species and origins. In contrast, acetone extractives, the total amount of phenolics and lignin showed significant differences. The concentration of phenolics and lignin was significantly higher in L. kaempferi and in L. × eurolepis than in L. decidua. The total phenolics content was strongly correlated with decay-resistance in all investigated larch origins. A higher concentration of phenolics goes hand in hand with higher decay resistance and phenolics might therefore be a promising parameter to rapidly evaluate the level of decay-resistance in larch.     

Protecting wood from mould,decay, and termites with multi-component biocide systems

Biocides must be developed for controlling mould establishment on cellulose-based building materials. Accordingly, biocides intended for indoor applications must be non-toxic, non-volatile, odourless, hypoallergenic, and able to provide long-term protection under conditions of high humidity. Multi-component biocide systems were tested in American Wood-Preservers’ Association soil block tests for inhibition of brown-rot and white-rot decay fungi and American Society for Testing and Materials standard tests for inhibition of mould fungi and termites. Multi-component systems combining a borate base supplemented with either 0.1% azole or 0.5% thujaplicin, performed well against the two brown-rot fungi Postia placenta and Gloeophyllum trabeum; the white-rot fungus Coriolus versicolor; the three mould fungi Aspergillus niger, Penicillium chrysogenum, and Trichoderma viride; and the subterranean termite Reticulitermes flavipes (Kollar). It was concluded that for interior applications borate-based multi-component biocide systems can protect wood from decay fungi, mould fungi, and termites, and that a system containing thiabendazole provided protection at a lower retention than the other biocides in this study. Synergy was observed between the borate base and voriconazole in inhibition of mould.     

Characterisation of the initial degradation stage of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) sapwood after attack by brown-rot fungus <Emphasis Type="Italic">Coniophora puteana</Emphasis>

In our study, early period degradation (10 days) of Scots pine (Pinus sylvestris L.) sapwood by the brown-rot fungus Coniophora puteana (Schum.: Fr.) Karst. (BAM Ebw.15) was followed at the wood chemical composition and ultrastructurelevel, and highlighted the generation of reactive oxygen species (ROS). An advanced decay period of 50 days was chosen for comparison of the degradation dynamics. Scanning UV microspectrophotometry (UMSP) analyses of lignin distribution in wood cells revealed that the linkages of lignin and polysaccharides were already disrupted in the early period of fungal attack. An increase in the lignin absorption A₂₈₀ value from 0.24 (control) to 0.44 in decayed wood was attributed to its oxidative modification which has been proposed to be generated by Fenton reaction derived ROS. The wood weight loss in the initial degradation period was 2%, whilst cellulose and lignin content decreased by 6.7% and 1%, respectively. Lignin methoxyl (–OCH₃) content decreased from 15.1% (control) to 14.2% in decayed wood. Diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy corroborated the moderate loss in the hemicellulose and lignin degradation accompanying degradation. Electron paramagnetic resonance spectra and spin trapping confirmed the generation of ROS, such as hydroxyl radicals (HO^∙), in the early wood degradation period. Our results showed that irreversible changes in wood structure started immediately after wood colonisation by fungal hyphae and the results generated here will assist in the understanding of the biochemical mechanisms of wood biodegradation by brown-rot fungi with the ultimate aim of developing novel wood protection methods.     

Hydrogels obtained from an original catanionic system for efficient formulation of boron wood-preservatives

A new catanionic system associating amphiphilic carnosine (βAlaHisC8) and lauric acid forms supramolecular hydrogel at a very low concentration. This gel was investigated and we checked the validity of the concept of hydrogel utilization to reduce boron leachability and to develop new wood protection treatments. Impregnation with 5% aqueous borax solution (w/w) and 0.3% gelator agent (w/w) fosters improvement in the resistance of Scots pine sapwood subjected to water leaching toward the brown-rot fungus Poria placenta, while samples treated with 5% aqueous borax solution were partially degraded by the fungus. These results clearly indicate the effectiveness of hydrogel to retain boron in wood.