Fungus Postia Placenta Research Articles

Exposure of Pinus elliottii wood treated with titanium dioxide to the fungus Postia placenta and photodegradation

It was impregnated commercial titanium dioxide into Pinus elliottii wood, aiming to increase its durability against the attack of brown rot fungus Postia placenta and photodegradation caused by ultraviolet radiation. The samples were put under 8 bar pressure for 3 hours at different concentrations of TiO2 (0.5%, 0.25%, 0.124% and 0%-control). To evaluate the effect of the fungus on the wood, the test was carried out according to ASTM D2017-05 and UNE-EN 113:1996 with modifications. The photodegradation was performed by exposing a tangential section to ultraviolet radiation for 400 hours, and the colorimetric parameters were periodically evaluated. Statistically, the treatments with TiO2 did not differ among themselves, but were much lower than the control, showing the effectiveness of this product in protecting the wood against the attacks of degraders. As for the photodegradation, the treated wood remained practically unchanged, differently from the control that had a darkening accelerated mainly in the first 50 hours. With this information, it can be stated that TiO2 treated wood is able to hinder the fungus access to the cell wall, to inhibit its growth and to create a barrier that protects the polymers from photodegradation, increasing its durability and emerging as a potential alternative for wood treatment.

Fluorescence in situ mRNA hybridization for gene expression detection in a wood decay fungus

Wood-degrading fungi efficiently decompose wood using a series of steps that are regulated across time and space. RNA sequencing with “bulk” sampling method has indicated processes controlled at the transcription level at different decay stages and locations along hyphal networks. To further understand these regulatory mechanisms, a high-resolution technique for gene expression determination is required. In this work, Fluorescence In Situ Hybridization (FISH) of mRNA was tested and optimized in the ‘brown rot’-type (carbohydrate-selective; lignin-rich residues) model fungus Postia placenta to image gene expression at the hyphal scale, <10 μm. The mRNA of one housekeeping gene Tef1α and three wood-decaying genes Cel28a, Cel5b and Qrd1 were tested in hyphae grown in liquid nutrients and wood substrate. The 20 bp-long DNA probes were successfully delivered intracellularly to give sufficient hybridization signal for imaging. Ahead of hybridization, permeabilization by lyticase and proteinase K treatments proved to be the critical step to increase probe and mRNA accessibility. Tyramide signal amplification was used after hybridization to enhance signal. This gave qualitative measures of mRNA of the four target genes, which were generally in line with previous expression patterns generated from coarser-scale RNA-seq and qRT-PCR studies. These techniques developed here were not without challenges, and future optimization using multiple probe fragments for each mRNA molecule is proposed.

Reference genes for accurate normalization of gene expression in wood-decomposing fungi

Wood-decomposing fungi efficiently decompose plant lignocellulose, and there is increasing interest in characterizing and perhaps harnessing the fungal gene regulation strategies that enable wood decomposition. Proper interpretation of these fungal mechanisms relies on accurate quantification of gene expression, demanding reliable internal control genes (ICGs) as references. Commonly used ICGs such as actin, however, fluctuate among wood-decomposing fungi under defined conditions. In this study, by mining RNA-seq data in silico and validating ICGs in vitro using qRT-PCR, we targeted more reliable ICGs for studying transcriptional responses in wood-decomposing fungi, particularly responses to changing environments (e.g., carbon sources, decomposition stages) in various culture conditions. Using the model brown rot fungus Postia placenta in a first-pass study, our mining efforts yielded 15 constitutively-expressed genes robust in variable carbon sources (e.g., no carbon, glucose, cellobiose, aspen) and cultivation stages (e.g., 15 h, 72 h) in submerged cultures. Of these, we found 7 genes as most suitable ICGs. Expression stabilities of these newly selected ICGs were better than commonly used ICGs, analyzed by NormFinder algorithm and qRT-PCR. In a second-pass, multi-species study in solid wood, our RNA-seq mining efforts revealed hundreds of highly constitutively expressed genes among four wood-decomposing fungi with varying nutritional modes (brown rot, white rot), including a shared core set of ICGs numbering 11 genes. Together, the newly selected ICGs highlighted here will increase reliability when studying gene regulatory mechanisms of wood-decomposing fungi.

Correction: Morphological Characterization and Quantification of the Mycelial Growth of the Brown-Rot Fungus Postia placenta for Modeling Purposes.

[This corrects the article DOI: 10.1371/journal.pone.0162469.].

Potential of teak heartwood extracts as a natural wood preservative

This study aimed to evaluate the preservative potential of teak (Tectona grandis) heartwood extracts against decay fungi. The waste obtained in the mechanical processing of 20-year-old teak wood was used to perform extractions in hot water and absolute ethanol. To evaluate the influence of teak extracts on the natural resistance of wood, a 10-year-old teak sapwood and Pinus sp. were used. To determine the concentration of the treatment solutions, a toxicity test to the brown rot fungus Postia placenta was performed. For the impregnation, a full-cell (Bethell) treatment was conducted. Biological assays with brown, white and soft-rot fungi were performed under laboratory conditions to test the efficiency of the teak extractive solutions. The solutions containing the absolute ethanol extractives promoted the best results in the decay resistance of the treated wood and significantly changed the resistance class of the respective treated species. The resistance to soft-rot fungi was not changed.

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

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.

Morphological Characterization and Quantification of the Mycelial Growth of the Brown-Rot Fungus Postia placenta for Modeling Purposes.

Continuous observation was performed using confocal laser scanning microscopy to visualize the three-dimensional microscopic growth of the brown-rot fungus, Postia placenta, for seventeen days. The morphological characterization of Postia placenta was quantitatively determined, including the tip extension rate, branch angle and branching length, (hyphal length between two adjacent branch sites). A voxel method has been developed to measure the growth of the biomass. Additionally, the tip extension rate distribution, the branch angle distribution and the branching length distribution, which quantified the hyphal growth characteristics, were evaluated. Statistical analysis revealed that the extension rate of tips was randomly distributed in space. The branch angle distribution did not change with the development of the colony, however, the branching length distribution did vary with the development of the colony. The experimental data will be incorporated into a lattice-based model simulating the growth of Postia placenta.

Strength properties and natural durability of Avocado (Persea americana Mill.) branch wood

This paper reports on mechanical properties and natural durability of avocado branch wood (Persea americana Mill.) with the objectives of providing a reliable property profile and to promote the rational use of this abundant yet largely neglected natural resource. The mechanical properties (static bending, compression, shear, impact bending) and hardness were determined in accordance with European standards (CEN). Natural durability was assessed according to the European standard EN 350-1 (agar block test) using the white rot fungi Trametes versicolor and Phanerochaete chrysosporium, and the brown rot fungus Postia placenta. Avocado trees yield a low to medium density (0,44-0,54-0,64 g/cm3 at 12% mc) branch wood with below average strength under static bending, compression and tension parallel to the grain and average values for longitudinal shear, impact bending and hardness. The wood is rated non-resistant (class 5 according to EN 350-1) and thus is not suitable for exterior applications unless treated. Considering its property profile and the small dimensions available, avocado wood is recommended for general carpentry, furniture, interior paneling, glue-boards for closets and cabinets, and glue-lams for indoor framework.

Molecular characterization of a novel thermostable laccase PPLCC2 from the brown rot fungus Postia placenta MAD-698-R

Laccase has been considered important for the degradation of lignocellulose by wood rot fungi. The properties and functions of laccase in white rot fungi have been investigated extensively, but those from brown rot fungi remain largely unknown. In this paper, a laccase isoform Pplcc2 from the brown rot fungus Postia placenta MAD-698-R was expressed heterologously in Pichia pastoris GS115, purified and the properties of the enzyme were determined. The molecular weight of the protein was determined to be 67 kDa using SDS-PAGE. It cannot oxidize syringaldazine (SGZ), but it can oxidize 2,2′-azino-di-(3-ethylbenzothialozin-6-Sulfonic acid) (ABTS) and 2,6-dimethoxyphenol (DMP). Specific activity for ABTS was 1960 ± 19 Unit/mg. The catalytic constant (kcat) was 1213 ± 18.3 s-1 for ABTS and 293.2 ± 21.9 s-1 for DMP. Km was 22.08 μM for ABTS and 11.62 μM for DMP. The optimal pH for the oxidation of ABTS and DMP was 3.5 and 5.0 respectively. The optimal temperature for the oxidation of ABTS and DMP was 60°C. This is the first identified thermo activated and thermostable laccase in brown rot fungi. This investigation will contribute to understanding the roles played by laccases in brown rot fungi.

Transcriptional profiles of laccase genes in the brown rot fungus Postia placenta MAD-R-698.

One of the laccase isoforms in the brown rot fungus Postia placenta is thought to contribute to the production of hydroxyl radicals, which play an important role in lignocellulose degradation. However, the presence of at least two laccase isoforms in this fungus makes it difficult to understand the details of this mechanism. In this study, we systematically investigated the transcriptional patterns of two laccase genes, Pplcc1 and Pplcc2, by quantitative PCR (qPCR) to better understand the mechanism. The qPCR results showed that neither of the two genes was expressed constitutively throughout growth in liquid culture or during the degradation of a woody substrate. Transcription of Pplcc1 was upregulated under nitrogen depletion and in response to a high concentration of copper in liquid culture, and during the initial colonization of intact aspen wafer. However, it was subject to catabolite repression by a high concentration of glucose. Transcription of Pplcc2 was upregulated by stresses caused by ferulic acid, 2, 6-dimethylbenzoic acid, and ethanol, and under osmotic stress in liquid culture. However, the transcription of Pplcc2 was downregulated upon contact with the woody substrate in solid culture. These results indicate that Pplcc1 and Pplcc2 are differentially regulated in liquid and solid cultures. Pplcc1 seems to play the major role in producing hydroxyl radicals and Pplcc2 in the stress response during the degradation of a woody substrate.

Efficacy of alternatives to zinc naphthenate for dip treatment of wood packaging materials

Research is being conducted to evaluate potential preservatives to replace zinc naphthenate (ZnN) for use in dip-treatment of wooden packaging materials. In this study, laboratory tests evaluated the efficacy of preservatives in protecting Southern pine and yellow poplar against decay fungi and termites. Nine preservatives were evaluated at one or two concentrations, and in some cases with two dip times. The results of this study indicate that higher concentrations of most of the preservatives evaluated will provide protection similar to or greater than that of ZnN. Four of the formulations provided protection equivalent to or greater than that of ZnN across all of the test organisms. Lower concentrations of some of the copper-based preservatives were less effective than ZnN in preventing colonization of Southern pine by the copper tolerant fungus Postia placenta, but most formulations were more effective than ZnN in protecting yellow poplar against white-rot fungi. The test formulations tended to be more effective than ZnN in preventing termite feeding on southern pine, but some were less effective than ZnN in protecting yellow poplar from termites. Efficacy was found to increase with preservative concentration in several cases, but did not increase with a longer dip time.

Ultrastructure and immunocytochemistry of degradation in spruce and ash sapwood by the brown rot fungus Postia placenta: Characterization of incipient stages of decay and variation in decay process

Aspects of the degradation of non-cellulosic polysaccharides (pectins, hemicelluloses) in spruce and ash sapwood by the brown rot fungus Postia placenta was investigated using transmission electron microscopy coupled with immunocytochemistry. Degradation of non-cellulosic polysaccharides and changes in ultrastructure were initiated in the compound middle lamella (CML)/middle lamella cell corner (MLcc) regions of xylem cells; sites that were remote from hyphal colonization in the cell lumen. Degradation of the S3 layer was also detected in both wood species at early stages of decay. Apart from early stages of attack, the degradation patterns differed greatly between spruce and ash. Spruce showed three patterns of hemicellulose degradation in the secondary cell walls of tracheids, while ash showed a single pattern in fibers. Spruce parenchyma cells also showed lower resistance to decay than tracheids, whereas ash parenchyma cells showed higher resistance than fibers. Together, degradation of xylem cells by P. placenta differs between spruce (softwood) and ash (hardwood) even though they show similar initial degradation in CML/MLcc regions and the S3 layer. The overall degradation patterns observed, particularly in spruce differ from previous ideas and generally accepted decay patterns produced by brown rot fungi in wood.

Identification and functional characterization of a novel fungal immunomodulatory protein from Postia placenta

In this study, a previously unknown fungal immunomodulatory protein (FIP), here called FIP-ppl, was identified from the basidiomycete fungus Postia placenta by searching its genome sequence database using known FIPs as baits, which was the first basidiomycete FIP to be identified outside the order of edible macro fungi. The gene FIP-ppl was synthesized and expressed in Escherichia coli to produce a glutathione S-transferase (GST) fusion protein. The fusion protein was purified on a GST affinity column and the protein tag was removed using in situ thrombin cleavage. The purified recombinant protein (rFIP-ppl) displayed hemagglutination activity toward rabbit red blood cells but not against human red blood cells. RFIP-ppl stimulated mouse splenocyte cell proliferation and enhanced interleukin-2 (IL-2) release. Antitumor assays indicated that rFIP-ppl had significant cell proliferation inhibitory activity and apoptotic effects in human tumor cells with more pronounced inhibiting proliferation and inducing apoptotic effects on gastric tumor cells (MGC823) than against hepatoma (HepG2) cells. This study confirms an alternative means of identifying, producing, and isolating new FIPs. It may provide convenient access to FIP-ppl with potential human therapeutic applications.

Postia placenta decay of acetic anhydride modified wood – Effect of leaching

It is well established that acetylation of wood by the use of acetic anhydride is able to impart a significant degree of decay resistance. The aim of this work was to study how a standardized leaching procedure with water (EN 84) affected the degradation of acetic anhydride modified samples by the brown rot fungi Postia placenta compared to no leaching prior to incubation. Three different levels (low, medium, and high) of acetic anhydride modified Southern yellow pine (SYP; Pinus spp.) were tested. The samples were harvested after 4 and 28 weeks. We compared changes in mass loss, wood moisture content, fungal DNA, and gene expression from five genes. If leaching changes the acetylated samples and makes them more susceptible for fungal deterioration, the expected effect would be higher levels of these parameters. Generally, leaching resulted in few differences between leached and nonleached samples at low levels of acetylation, while no changes were found for the highest acetylation level. No differences were found in gene expressions after 28 weeks. The possible protection of acetylated wood against oxidative fungal degradation is suggested to be interpreted in combination with the lowered wood moisture content.

Biological Durability of Oil Heat Treated Alder Wood

The article presents preliminary results of the biological durability of oil heat treated (OHT) alder wood (Alnus glutinosa) against pure cultures of rot fungi (Postia placenta and Trametes versicolor) in lab condi- tions. The modifi cation was performed by heating of specimens immersed in soya oil. There were four heating regimes of different duration (6 and 10 hours) at fi nal temperature of 180 and 200 oC. The increase in mass (MI) caused by modifi cation and mass loss of wood caused by fungal decay (ML) were determined. In addition, the natural durability of alder wood was determined and compared to the natural durability of beech wood as the reference wood species. After modifi cation of alder wood at 200 °C, MI was lower than after treatment at 180 °C. MI was also lower after 10 hours of treatment than after 6 hours of treatment. The results showed signifi cantly increased biological dura- bility of modifi ed alder wood against both tested fungi. The effect of OHT on increasing the biological durability of alder wood was higher against the fungus P. placenta. It seems that the fungus T. versicolor favours the remained oil after modifi cation causing higher mass loss. The results showed that alder wood, thermally modifi ed in soya oil by testing regimens, is not suitable for applications in use classes 3-5.

The activity of rot fungi (Postia placenta) during drying and rewetting cycles measured by isothermal calorimetry

Rot fungi are a major problem in the construction sector, and method to study under which moisture and temperature coefficients they grow are therefore of significant interest. Measurements of heat production rate have been made on wood samples with the brown rot fungus Postia placenta at different moisture contents (MCs). The results clearly show the heat production rate (a measure of respiration rate and fungal activity) is moisture‐dependent. For most cases, less heat was produced when the MC was decreased, and more heat was produced when the MC was increased. It was also found that when the MC increased after a dry period, the increase in activity was significantly delayed. However, if the moisture state was then kept constant at a high level, the activity slowly increased, showing that the fungi need time to recover back to the original activity level after drying. Isothermal calorimetry is a measurement technique well suited for the study of the activity of wood‐decaying fungi as a function of temperature and moisture content.

Influence of wood durability on the suppressive effect of increased temperature on wood decay by the brown-rot fungus Postia placenta

Abstract Local climate conditions have a major influence on the biological decomposition of wood. To examine the influence of different temperature regimes on wood decay caused by the brown rot fungus Postia placenta in wood with differing natural durability, sapwood (sW) and heartwood (hW) of Scots pine, inoculated mini-blocks were incubated for up to 10 weeks at temperatures conducive or above optimal to wood decay. We profiled mass loss (ML) and wood composition, and accompanying changes in wood colonization and transcript level regulation of fungal candidate genes. The suppressive effect of suboptimal temperature on wood decay caused by P. placenta appeared more pronounced in Scots pine hW with increased durability than in sW with low decay resistance. The differences between sW and hW were particularly pronounced for cultures incubated at 30°C: unlike sW, hW showed no ML, poor substrate colonization and marker gene transcript level profiles indicating a starvation situation. As brown rot fungi show considerable species-specific variation in temperature optima and ability to mineralize components that contribute to wood durability, interactions between these factors will continue to shape the fungal communities associated to wood in service.

Colocalizing incipient reactions in wood degraded by the brown rot fungus Postia placenta

Brown rot fungi are theorized to use both free radicals and enzymes to degrade wood. If these incompatible agents are employed in sequence (enzymatic after oxidative) in order to avoid interaction, this should be resolvable spatially in rotting wood. To assess this, we used thin spruce wafers as substrates, with the largest face the transverse plane. Propped wafers were colonized from the bottom (tangential to grain) by Postia placenta, using wood cell orientation and gravity to slow fungal egress and accentuate spatial gradients. After brief colonization, wafers were cut into 1-mm strips progressing up the wafer, and subsectioned for complementary analyses. Analyses included fungal growth, pH, cellulase activity, and wood modifications attributable to non-enzymatic mechanisms. Hyphae were imaged using confocal microscopy of fluorophore-tagged chitin. Dilute alkali solubility and lignin demethylation were measured as proxies (consequences) of carbohydrate depolymerization and lignin oxidation, respectively. Because P. placenta lacks genes for cellobiohydrolases, endoglucanase (EG) activity was measured. In composites of reassembled sections, hyphal fronts and apparent depolymerization preceded EG and lignin demethylation fronts by more than 6 mm. Although detection limits are a caveat when implicating novel fungal metabolites, results encourage and provide methodology for targeting this interesting leading edge of cellulolysis.

Fungal biodegradation of genetically modified and lignin-altered quaking aspen (Populus tremuloides Michx.)

AbstractBetter access to wood carbohydrates as a result of reduced, or altered, lignin is a goal of biopulping, as well as biofuel research. In the present article, woods from three transgenic trees and one wild-type quaking aspen (Populus tremuloidesMichx.) were analyzed in terms of mass loss of cellulose and lignin after incubation with lignocellulolytic fungi. The transgenic trees had reduced lignin content through transfer of an antisense -4CL gene, elevated syringyl/guaiacyl (S/G) ratio through insertion of a sense CAld5H gene and low lignin content and elevated S/G ratio through simultaneous insertion of -4CL and CAld5H genes, respectively. The lignocellulolytic fungi employed were a lignin-selective white rot fungusCeriporiopsis subvermispora, a simultaneous white rot fungusTrametes versicolorand a brown rot fungusPostia placenta. Reduced lignin degradation was observed in woods with increased S/G ratios indicating that this analytical feature influences decay resistance, regardless of the fungal decay mechanism.

Varietal difference in antifungal activity of some species of Agave

Crude leaf extracts of different Agave species were eluted out with the help of 80% methanol for their antifungal activity. The activity of A. americana, A. ferox, A. montana, A. marginata, and A. scabra were evaluated against brown rot fungi Postia placenta, the causal agent of wood decay of some economically important plants using a media poising method. The percent inhibition of hyphal growth was measured after the seventh day of incubation. A. montana shows the highest percent inhibition, 69.31%, of hyphal growth. These data suggested that the different Agave species analyzed have potential as antifungal agents with a broad range of activity. In the future they may be used as biocontrol agents to cure plant diseases without harming them.