Soft Rot Fungi Research Articles

Condensed conifer tannins as antifungal agents in liquid culture

Abstract In the last decades, many wood preservatives have been prohibited for their ecotoxicity. The present article is focusing on the conifer-derived condensed tannins as environment-friendly options for the substitution of artificial wood preservatives. Eight different tannin fractions were extracted from spruce cones, spruce barks, and pine cones. The parameters of tannin extraction, such as the methods of purification and concentration of active components in the extracts, have been investigated. The cone and bark extracts were tested for the growth inhibition of eight brown-rot fungi, three white-rot fungi, and four soft-rot fungi in liquid cultures. The cone tannins provided a more efficient fungal growth inhibition than bark tannins. Purification increased the antifungal properties of the extracts. The growth of brown-rot fungi was inhibited by the tannins already at low concentrations. However, the extracts were not effective against the white-rot or soft-rot fungi. More investigation is needed concerning the tannin source and the purification procedure of the extracts before tannins can be considered as an ecologically benign wood preservative.

In-vitro studies on wood degradation in soil by soft-rot fungi: Aspergillus niger and Penicillium chrysogenum

This paper focuses on the biodegradation of wood by two soft-rot fungi, Aspergillus niger and Penicillium chrysogenum, in soil which was artificially infested. The structural changes of pine and sycamore wood were evaluated by scanning electron microscope (SEM). Surprisingly, soft-rot fungi tolerate low moisture to cause extensive decay in the wood samples. The micrographs showed differences in hyphae colonization and wood degradation patterns between soft-rot species under this study; A. niger produced soft-rot decay type I (cavity formation) and soft-rot decay type II (erosion), while P. chrysogenum caused only soft-rot decay type II.

Selection and validation of enzymatic activities as functional markers in wood biotechnology and fungal ecology

The dead wood and forest soils are sources of diversity and under-explored fungal strains with biotechnological potential, which require to be studied. Numerous enzymatic tests have been proposed to investigate the functional potential of the soil microbial communities or to test the functional abilities of fungal strains. Nevertheless, the diversity of these functional markers and their relevance in environmental studies or biotechnological screening does still have not been demonstrated. In this work, we assessed ten different extracellular enzymatic activities involved in the wood decaying process including β-etherase that specifically cleaves the β-aryl ether linkages in the lignin polymer. For this purpose, a collection of 26 fungal strains, distributed within three ecological groups (white, brown and soft rot fungi), has been used. Among the ten potential functional markers, the combinatorial use of only six of them allowed separation between the group of white and soft rot fungi from the brown rot fungi. Moreover, our results suggest that extracellular β-etherase is a rare and dispensable activity among the wood decay fungi. Finally, we propose that this set of markers could be useful for the analysis of fungal communities in functional and environmental studies, and for the selection of strains with biotechnological interests.

The wood preservative potential of long-lasting Amazonian wood extracts

Investigations were carried out on the efficacy of extracts from seven Amazonian woods (Bagassa guianensis, Manilkara huberi, Sextonia rubra, Vouacapoua americana, Andira surinamensis, Handroanthus serratifolius, and Qualea rosea) with varying natural durability to reduce soft-rot degradation in a 6-wk soil-bed test. Six of the wood extracts had shown efficacy against soft-rot fungi. In particular, the preservation efficacies of B. guianensis, H. serratifolius, and S. rubra extracts were highly significant up to retention levels of 23, 25, and 12 kg m−3, respectively. Three extracts (A. surinamensis, H. serratifolius, and Q. rosea) were then tested against Gloeophyllum trabeum (brown rot) and Trametes versicolor (white rot), in an agar-block test. H. serratifolius wood extract was very efficient at protecting P. sylvestris samples at 5.1 kg m−3 against the brown rot. This extract could be used as a basis for new wood protectant formulations.

Durability of oak timber bridges – Impact of inherent wood resistance and environmental conditions

Premature failure of timber construction can have dramatic consequences, at worst threat to human life or physical condition. Timber components might perform unexpectedly poor due to insufficient protection by misuse, design, low work execution level, or due to low resistance of the material in use. However, information about the material resistance of prematurely failed structures is usually lacking. Therefore this study aimed on developing a method to display the relationship between damages occurring on structures in service and the resistance against wood-destroying fungi of the material used.Drilling cores taken from wooden structures were found to have the ability to serve as specimens in laboratory decay test when compared to standard specimens. Therefore, drilling cores were sampled from different components of six timber bridges in Hannover, Germany, made from English oak (Quercus robur L.). The cores were submitted to the white rot fungus Trametes versicolor and to soft rot fungi in terrestrial microcosms. The determined mass losses due to fungal decay were compared with the level of damage of the studied bridge components. The results indicated that the material-inherent resistance was responsible for damages rather than poor details of the construction. The methodological approach might be used to provide further knowledge about the relationship of timber in service and under ideal laboratory test conditions.

The Wood Rot Ascomycete Xylaria polymorpha Produces a Novel GH78 Glycoside Hydrolase That Exhibits α- l -Rhamnosidase and Feruloyl Esterase Activities and Releases Hydroxycinnamic Acids from Lignocelluloses

Soft rot (type II) fungi belonging to the family Xylariaceae are known to substantially degrade hardwood by means of their poorly understood lignocellulolytic system, which comprises various hydrolases, including feruloyl esterases and laccase. In the present study, several members of the Xylariaceae were found to exhibit high feruloyl esterase activity during growth on lignocellulosic materials such as wheat straw (up to 1,675 mU g(-1)) or beech wood (up to 80 mU g(-1)). Following the ester-cleaving activity toward methyl ferulate, a hydrolase of Xylaria polymorpha was produced in solid-state culture on wheat straw and purified by different steps of anion-exchange and size-exclusion chromatography to apparent homogeneity (specific activity, 2.2 U mg(-1)). The peptide sequence of the purified protein deduced from the gene sequence and verified by de novo peptide sequencing shows high similarity to putative α-L-rhamnosidase sequences belonging to the glycoside hydrolase family 78 (GH78; classified under EC 3.2.1.40). The purified enzyme (98 kDa by SDS-PAGE, 103 kDa by size-exclusion chromatography; pI 3.7) converted diverse glycosides (e.g., α-L-rhamnopyranoside and α-L-arabinofuranoside) but also natural and synthetic esters (e.g., chlorogenic acid, hydroxycinnamic acid glycoside esters, veratric acid esters, or p-nitrophenyl acetate) and released free hydroxycinnamic acids (ferulic and coumaric acid) from arabinoxylan and milled wheat straw. These catalytic properties strongly suggest that X. polymorpha GH78 is a multifunctional enzyme. It is the first fungal enzyme that combines glycosyl hydrolase with esterase activities and may help this soft rot fungus to degrade lignocelluloses.

Microbial degradation of waterlogged archaeological wood

Abstract Waterlogged archaeological wood is degraded very slowly compared to wood decay above ground. The special environmental conditions below ground, results in a prolonged decay process that under extremely low oxygen concentration only allow bacterial degradation of wood. The so-called erosion bacteria are described and waterlogged archaeological wood is defined. Soft rot fungi are other microbes that often are found active in more oxygenated aquatic environment. A short historic review on the understanding of waterlogged archaeological wood and the different decay processes is given and exemplified. Knowledge on decay processes is essential for development of conservation methods and in situ preservation of wooden cultural heritage.

RNA reveals a succession of active fungi during the decay of Norway spruce logs

Current knowledge of the succession of fungi in decaying wood is mostly based on fruit bodies and in vitro culture. Here, we investigated the changing community of metabolically active fungi during the decomposition of fallen Picea abies logs by directly extracting and barcode sequencing precursor rRNA. We also compared rRNA-derived amplicons of the 18S and ITS regions in 21 isolates and discuss the use of RNA as a marker of metabolically active fungi. The richness of active fungi, revealed as separated bands in DGGE, peaked in logs at an advanced stage of decay. Soft-rot fungi were common in the early stages but white- and brown-rot fungi became dominant as decay progressed. Ectomycorrhizal fungi were detected at an early stage, and they became the most abundant group in the late stages of succession. A comparison of rRNA-derived amplicons revealed that although ITS was detected in the form of precursor rRNA, introns within 18S rDNA were already spliced. As such, rRNA- and rDNA-derived amplicons would yield different profiles of active and total communities if profiling method is affected by amplicon length.

Fungal degradation of bamboo samples

Abstract The degradation of several Asian bamboo species by white-, brown-, and soft-rot fungi was investigated under laboratory conditions by means of different test methods. Severe deterioration was caused by all three fungi types. The bamboo species differed in durability. Samples from 6 months young culms decayed more than older ones. There were no significant differences between 1- and 3-year-old culms. Samples taken from the culm top were more vulnerable to decay than those from the bottom. Wet bamboo samples with soil contact were especially degraded by the white-rot fungus Schizophyllum commune, whereas the brown-rot fungus Coniophora puteana produced the greatest mass loss in drier samples. The sealing of bamboo crosscut ends reduced the rate of decay.

Biodegradation of polyurethane acrylate with acrylated epoxidized soybean oil blend elastomers by Chaetomium globosum

This paper studies the biodegradation features of a novel blend of polyurethane acrylate–acrylated epoxidized soybean oil-based cross-linked polyurethane elastomers in the presence of the soft-rot fungus Chaetomium globosum. After the specimens were incubated at 28 °C for 90 and 130 days, the degree of fungal damage was measured by analysis of weight loss and mechanical properties. The biodegradation of the films was also evidenced by SEM and FTIR spectroscopic studies. After fungal attack, the FTIR spectra indicate a degradation of urethane and ester groups of the polyurethane and especially of the ester groups from the modified soybean oil part. The polyurethane blend films exposed to fungal attack suffered a loss in strength of up to 55% and a loss in elongation of up to 80%, depending on the content of acrylated epoxidized soybean oil. The biodegradation of the blends was also confirmed by SEM analyses. The biodegradation results show that samples with a high content of acrylated epoxidized soybean oil are more biodegradable than mere polyurethane acrylate. These biodegradable polymer blends present an optimum balance of physical properties and biodegradable properties with the potential for application as eco-friendly biomaterials.

Anti-Fungal Activity Characterization of Four Rosinyl Quaternary Ammonium Salts

The anti-fungal activities of four self-prepared rosinyl quaternary ammonium salts (QAS), QASA, BQAS1, BQAS2 and DQAS, were evaluated with paper disc method in this paper. The result showed that, all the QAS of rosin were bioactive to the selected fungi, Irpex lacteus, Trametes versicolor, Phanerochaete chrysosporium, Gloeophyllum trabeum, Chaetomium globosum, and Paecilomyces variotii. There were obvious inhibition halos for all QAS to the fungi. The result proved that the QAS of rosin were broad-spectrum anti-fungal. Especially, to white rot fungus Trametes versicolor, brown rot fungus Gloeophyllum trabeum and soft rot fungus Chaetomium globosum, they were more effective. When the concentration reached 3.2% (w/w), the inhibition halo diameters all met or exceeded 25mm. Among these four anti-fungal derivatives of rosin, the Gemini QAS (BQAS1 and BQAS2) had bigger inhibition halo diameters than the others, which indicated that the Gemini QAS of rosin were more anti-fungal than the normal QAS of rosin.

Fungal colonization of coastal Douglas-fir following mechanical commercial thinning damage

Commercial-aged Douglas-fir trees mechanically damaged during commercial thinning activities were investigated to quantify fungal taxa present 14years after thinning. A total of 235 wood cores from 18 damaged and 18 non-damaged control trees were obtained. Fungi were isolated on malt extract agar and molecular methods were used to identify 48 taxa. Damaged Douglas-fir trees were more than twice as likely to contain wood-inhabiting fungi as undamaged trees (p=0.07) and contained more than 2.5 times more fungi (p=0.006). However, typical Douglas-fir stem-decay fungi were not isolated. Fungi present were mostly endophytes and no significant differences were found in frequencies of decay/non-decay soft-rot fungi between damaged and control trees (p=0.67). Likewise, no significant differences were found for the trend in number of fungi isolates over radial depth into the stem between damaged and control trees (p=0.29). Frequency of fungal isolates was non-linearly related to depth in the tree bole. Significant differences between damaged and control trees (p=0.03) was influenced by the data in the outermost 3mm. With the exception of these data, there were no significant differences between damaged and control trees in the radial trend in fungal frequency (p=0.37). Results of this study suggest that wounding in commercial-aged Douglas-fir may not contribute significantly to occurrence and species composition of wood inhabiting fungi over the period of a short-rotation final harvest. However, damage mitigation is recommended supported by a related study showing vertical discolouration affecting all wounded stems. © 2010 Blackwell Verlag GmbH.

Fungal deterioration of a Jesuit South American polychrome wood sculpture

Pigment samples obtained from a South American Jesuit wooden sculpture housed at the Museum of Natural Sciences in La Plata, Buenos Aires province, Argentina, were characterized using scanning electron microscopy and energy dispersive X-ray microanalysis and infrared spectroscopy. The red pigments were identified as vermilion and minium, while the mineral pigment green earth was identified for the first time in a Colonial artwork, together with calcite as the plaster. Two fungal species, Nigrospora sphaerica (Sac.) Mason and Chaethomium globosum Kunze, were isolated from a sample of wood, which was identified as Cedrela fissilis. Chaetomium is a known soft-rot fungus with the capacity to decay wood, but little is known about the effects of Nigrospora on wood. The presence of the two fungi in decayed areas of the wood suggests a contribution of both of them to the degradation of the sculpture.

Characterization of Fungal-Degraded Lime Wood by X-Ray Diffraction and Cross-Polarization Magic-Angle-Spinning 13C-Nuclear Magnetic Resonance Spectroscopy

X-ray diffraction, scanning electron microscopy (SEM), and solid-state cross-polarization magic-angle-spinning (CP/MAS) (13)C-NMR spectroscopy were applied to determine changes over time in the morphology and crystallinity of lime wood (Tilia cordata Miller) generated by the soft-rot fungi. Wood samples were inoculated with Trichoderma viride Pers for various durations up to 84 days. Structural and morphological modifications were assessed by comparing the structural features of decayed lime wood samples with references. Significant morphology changes such as defibration or small cavities were clearly observed on the SEM micrographs of lime wood samples exposed to fungi. Following the deconvolution process of the diffraction patterns, the degree of crystallinity, apparent lateral crystallite size, the proportion of crystallite interior chains, and the cellulose fraction have been determined. It was found that all crystallographic data vary with the duration of exposure to fungi. The degree of crystallinity and cellulose fraction tend to decrease, whereas the apparent lateral crystallite size and the proportion of crystallite interior chains increase with prolonged biodegradation processes. The most relevant signals in CP/MAS (13)C-NMR spectra were assigned according to literature data. The differences observed were discussed in terms of lignin and cellulose composition: by fixing the lignin reference signal intensity, the cellulose and hemicelluloses moieties showed a relative decrease compared to the lignin signals in decayed wood.

Dependence of fungal biodegradation of PEG/castor oil-based polyurethane elastomers on the hard-segment structure

In the context of protecting of the environment, this work studies the biodegradation of PEG-based polyurethane elastomer films in the presence of the soft rot fungus Chaetomium globosum, determined via the Petri-dish test. Using PEG with high-molecular weight (MW = 1500) as a chain extender led to polyurethane elastomers with lower physical crosslink density and higher swelling rates. The structural modifications in the hard-segment area (C O and N–H peaks) are considerable and were analyzed by FTIR spectroscopy. Biodegradation lowers the final mechanical properties, but increases yield points, especially in the case of polyurethane elastomers crosslinked with castor oil. Polyurethane elastomer samples showed visible degradation proved by the mechanical weakening of the films. Thus, breaking strains decrease from 670–1180% to 500–680% and tensile strengths decreased from 11.5–27.5 MPa to 4–11.5 MPa after 130 days of fungal biodegradation. The changes in the morphology of the polyurethane films surface were analyzed by SEM and have been found to exhibit increasing porous structure and fungal hyphae. The effects of the hard-segment composition of the polyurethane elastomers on the fungal biodegradation behaviour were investigated.

Novel bifunctional alpha-L-arabinofuranosidase/xylobiohydrolase (ABF3) from Penicillium purpurogenum.

The soft rot fungus Penicillium purpurogenum grows on a variety of natural substrates and secretes various isoforms of xylanolytic enzymes, including three arabinofuranosidases. This work describes the biochemical properties as well as the nucleotide and amino acid sequences of arabinofuranosidase 3 (ABF3). This enzyme has been purified to homogeneity. It is a glycosylated monomer with a molecular weight of 50,700 and can bind cellulose. The enzyme is active with p-nitrophenyl alpha-L-arabinofuranoside and p-nitrophenyl beta-D-xylopyranoside with a K(m) of 0.65 mM and 12 mM, respectively. The enzyme is active on xylooligosaccharides, yielding products of shorter length, including xylose. However, it does not hydrolyze arabinooligosaccharides. When assayed with polymeric substrates, little arabinose is liberated from arabinan and debranched arabinan; however, it hydrolyzes arabinose and releases xylooligosaccharides from arabinoxylan. Sequencing both ABF3 cDNA and genomic DNA reveals that this gene does not contain introns and that the open reading frame is 1,380 nucleotides in length. The deduced mature protein is composed of 433 amino acids residues and has a calculated molecular weight of 47,305. The deduced amino acid sequence has been validated by mass spectrometry analysis of peptides from purified ABF3. A total of 482 bp of the promoter were sequenced; putative binding sites for transcription factors such as CreA (four), XlnR (one), and AreA (three) and two CCAAT boxes were found. The enzyme has two domains, one similar to proteins of glycosyl hydrolase family 43 at the amino-terminal end and a family 6 carbohydrate binding module at the carboxyl end. ABF3 is the first described modular family 43 enzyme from a fungal source, having both alpha-L-arabinofuranosidase and xylobiohydrolase functionalities.

The biological behaviours of pine wood modified with linear chain carboxylic acid anhydrides against soft rot fungi

The work described in this paper has demonstrated that chemically modified Corsican pine sapwood with a homologous series of linear chain carboxylic acid anhydrides afforded bioprotection against soft rot decay. By varying the reaction time, various levels of modifications were obtained. The results indicated that the breakdown caused by fungi is reduced by chemical modification at these levels of modification. There was no significant reduction in feeding above 20% WPG (weight percent gain due to modification) suggesting that modification to WPGs greater this certain level did not cause additional protection. The type of anhydride employed had little influence on breakdown behaviour.

Thermal behavior of biodegraded lime wood

The effects of the soft-rot fungus Trichoderma viride Pers., on the thermal behavior of lime wood ( Tillia cordata Mill .) were investigated. The lime wood pieces were inoculated with the fungus over a 12-week period. At pre-established time intervals two samples were withdrawn from the medium and analyzed by thermogravimetry and differential calorimetry, and the results were correlated with mass loss. Fungal activity was indicated by continuous decrease of sample mass. Modification of the wood because of the presence of the fungus was evidenced by structural changes that affected its thermal properties, both in respect to the hydrophilicity of the wood (evidenced mainly in desorption process) and in its decomposition behavior. The shape of DTG curves depends on the exposure time of wood to the action of microorganisms. The peak temperature assigned to the decomposition of wood components increases, while the global kinetic parameters for the main peak decrease with increasing exposure time of the wood to the attack by microorganisms. The increased characteristic temperatures of water desorption and cellulose decomposition processes and lower thermal stability could be explained by newly formed structures, mainly the oxidized ones.

Characterization of fungal degraded lime wood by FT-IR and 2D IR correlation spectroscopy

Abstract The action of soft-rot fungus Chaetomium globosum has been studied. The decayed lime wood samples were observed for different periods of exposure. The degree of decay was determined by weight loss which was of 50.4% after 133 days. The samples were analyzed by FT-IR and 2D IR correlation spectroscopy. The intensity bands assigned to different vibrations from cellulose and hemicelluloses show a decrease, while the intensities of the bands assigned to C–O vibrations due to the formation of oxidized structures increase. At the same time, the intensity of the band assigned to C–O in metoxyl groups from lignin shows a decrease with increasing exposure time. The differences between reference and decayed wood spectra were examined in detail using 2D correlation spectroscopy and the second derivative analysis for two exposure time periods — of 0–70 days and 70–133 days. The formation of reactive species due to oxidation reactions induced by enzymes and the demethoxylation of the lignin structure was evidenced.

Evaluation of Compressive Strength of Decayed Wood in Magnolia obovata

To obtain the basic information needed to estimate the degree of decay from compressive strength measured using a Fractometer (CS), relationships between CS and the contents of chemical components were analyzed for Magnolia wood decayed by three types fungi (brown rot, white rot, and soft rot fungi) at various decay levels. Weight loss ratio was significantly, negatively correlated with CS in woods decayed by brown rot and white rot fungi. In addition, a relatively high correlation coefficient was recognized between CS and holocellulose or α-cellulose content, except for wood decayed by soft rot fungus. The results obtained showed that Fractometer can detect the decrease of CS at relatively early stage of decay.