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. 2020 Dec 4;8(12):1931.
doi: 10.3390/microorganisms8121931.

Comparison of the Decay Behavior of Two White-Rot Fungi in Relation to Wood Type and Exposure Conditions

Ehsan Bari  1 , Geoffrey Daniel  2 , Nural Yilgor  3 , Jong Sik Kim  4 , Mohammad Ali Tajick-Ghanbary  5 , Adya P Singh  6 , Javier Ribera  7
Affiliations

Comparison of the Decay Behavior of Two White-Rot Fungi in Relation to Wood Type and Exposure Conditions

Ehsan Bari et al. Microorganisms. .

Abstract

Fungal wood decay strategies are influenced by several factors, such as wood species, moisture content, and temperature. This study aims to evaluate wood degradation characteristics of spruce, beech, and oak after exposure to the white-rot fungi Pleurotusostreatus and Trametesversicolor. Both fungi caused high mass losses in beech wood, while spruce and oak wood were more resistant to decay. The moisture content values of the decayed wood correlated with the mass losses for all three wood species and incubation periods. Combined microscopic and chemical studies indicated that the two fungi differed in their decay behavior. While T. versicolor produced a decay pattern (cell wall erosion) typical of white-rot fungi in all wood species, P. ostreatus caused cell wall erosion in spruce and beech and soft-rot type I (cavity formation) decay in oak wood. These observations suggest that P. ostreatus may have the capacity to produce a wider range of enzymes/radicals triggered by the chemical composition of wood cell walls and/or local compositional variability within the cell wall.

Keywords: Pleurotus ostreatus; Trametes versicolor; soft-rot and simultaneous white-rot; white-rot.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. No funding sources had any role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Mass loss (ML) and moisture content (MC) of wood decayed by the white-rot fungus Pleurotus ostreatus for 60 days incubation. Average of twelve replicates ± SD. t-test p < 0.05.
Figure 2
Figure 2
Mass loss (ML) and moisture content (MC) of wood decayed by the white-rot fungus Trametes versicolor for 60 days incubation. Average of twelve replicates ± SD. t-test p < 0.05.
Figure 3
Figure 3
Total FT-IR spectra of spruce wood samples exposed to T. versicolor (A) and P. ostreatus (B) for 60 days.
Figure 4
Figure 4
Total FT-IR spectra of beech wood samples exposed to T. versicolor (A) and P. ostreatus (B) for 60 days.
Figure 5
Figure 5
Total FT-IR spectra of oak wood samples exposed to T. versicolor (A) and P. ostreatus (B) for 60 days.
Figure 6
Figure 6
Morphology of fungal hyphae of P. ostreatus found in decayed beech and oak wood (A) and (B) fungal hyphae in beech were thin (arrow in A) with clamp connections (arrowheads in insets of B). (C,D) Fungal hyphae in oak were much thicker than that in beech (A,B). No clamp connections were noted (D) Scale bars: 30 µm.
Figure 7
Figure 7
LM observations of spruce wood decayed by P. ostreatus and T. versicolor. (A–C) Decay by P. ostreatus showing early stages of decay in both earlywood (EW; A,B) and latewood (LW, C). Note formation of decay zone (arrowheads) in some LW fibers (C). (D–F) Decay by T. versicolor showing more advanced stages of decay than P. ostreatus (A), particularly LW regions (F). Note formation of decay zones (arrowheads) in EW (E) and LW fibers (F). Scale bars: 20 µm.
Figure 8
Figure 8
LM observations of beech wood decayed by P. ostreatus and T. versicolor. The beech wood observed showed the presence of gelatinous fibers (arrows in B,E). (A–C) Decay by P. ostreatus showing fiber degradation by thinning of the cell wall from the lumen outwards. Note degradation of the middle lamella (ML) regions prior to complete degradation of the fiber secondary cell wall (arrowheads in B,C). (D–F) Decay by T. versicolor showing advanced stages of decay in fibers by thinning cell walls from the lumen outwards. Note, degradation of ML regions of fibers, with only remaining middle lamella cell corner (MLcc) regions (F). Degradation of the vessel (v) and axial parenchyma cell (ap) was less significant than fibers (F). Scale bars: 20 µm.
Figure 9
Figure 9
LM observations of oak wood decayed by P. ostreatus and T. versicolor. (A–C) Decay by P. ostreatus showing numerous cavities (arrowheads) in the secondary cell wall of (libriform) fibers (f, B) and (vasicentric) tracheids (vt, C). Cavities were frequently coalesced, with only remaining innermost cell walls (C). Note formation of cavities in the vessel (v) and axial parenchyma (ap) cell wall (arrows in C). (D–F) Decay by T. versicolor showing the degradation of fibers (E) and trachieds (C) by thinning of secondary cell wall from the lumen outwards. Note degradation of fibers through pits (arrows in E) and advanced stages of decay in the vessel and axial parenchyma cell walls (D,F). Scale bars: 20 µm.
Figure 10
Figure 10
TEM observations of oak wood decayed by P. ostreatus. Formation of cavities (asterisks) in the secondary cell wall of the (libriform) fiber (f, A), (vasicentric) tracheid (vt, B–D), and axial parenchyma cell (ap, C) with remnants of the innermost S3 layer (arrows in A–D). Note accumulation of electron-dense materials around fungal hyphae in cavities (arrowheads in A–C). Inset in (D) indicates fungal attack through intercellular spaces between tracheids associated with axial parenchyma cells. Scale bars: 1 µm.
Figure 11
Figure 11
TEM observations of oak wood decayed by T. versicolor. Thinning of the secondary cell wall of a (libriform) fiber (f, A), (vasicentric) tracheid (vt, B–D), and apical parenchyma cell (ap, D) from the lumen outwards. Note degradation of the middle lamella and the secondary cell wall through intercellular spaces and electron-lucent regions between tracheids associated with apical parenchyma cells (arrows in C,D). Pit membranes between tracheids showed high decay resistance and strong electron density (arrowheads in B,D). Scale bars: 1 µm.
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