The Fungal Decay Of Wood 1 1

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  • The first mode of attack brings pectolytic enzymes which are produced from the tips of soft rot hyphae. This breaks down the pectic acid, holding the cells together, leading to cell separations and a partial degradation of the hosts cell wall. This degradation of the cell wall causes secretions of watery nutrient sources out of the cell giving rise to its soft watery appearance. Once a weak point in the cell wall is in place, the hyphae can penetrate through and then produce broader hyphae once inside. Then they produce the cellulase enzymes which cause generalized decay of cellulose in a rhomboidal shape
  • Brown rot fungi can operate in dryer conditions as they obtain their water from the breakdown of cellulose. Cellulase enzymes created by fungi, have little or no impact on the cellulose that it is attacking therefore the breakdown relies on the breakdown of the weaker hemicelluloses. This breakdown is actually an oxidation process in which hydrogen peroxide is formed. Hydrogen peroxide is a strong oxidiser and readily causes generalized decay, leaving the lignin intact, maintaining the general cell shape
  • White rot is capable of breaking down all major components of the wood. The fungi appear to use conventional cellulase enzymes to breakdown the hemicelluloses and cellulose, exposing the lignin. The lignin is very difficult to breakdown and white rot fungi is the only known living organism to do so. The lignin is a complex polymer but the fungi seem to only require a few enzymes to break its different chains down. Again this is an example of an oxidation process with strong oxidisers such as hydrogen peroxide, lignin peroxidase and laccase. The reactions themselves are very complicated but result is a ‘combustion’ of lignin framework. The resultant molecules can become fungi toxic to the fungi so it detoxifies it by polymerisation.
  • The Fungal Decay Of Wood 1 1

    1. 1. The Fungal decay of wood By Noel Wallis, James Welburn, Charlene Wenn and Matthew Wheeler
    2. 2. Abstract
    3. 3. Fungi involved in wood decay <ul><li>Wood decay bacteria can be grouped in different ways: </li></ul><ul><li>by their method of degrading wood </li></ul><ul><li>by their general biology, pathogens , parasites or saprotrophs </li></ul><ul><li>whether they are primary colonizers or secondary colonizers </li></ul><ul><li>There are 3 different types of wood decaying bacteria </li></ul>
    4. 4. Soft-rot fungi <ul><li>Degrade cellulose and hemicelluloses </li></ul><ul><li>Occur in wood of high water content and high nitrogen content. </li></ul><ul><li>Found in rotting window frames, wet floor boards and fence posts, etc </li></ul><ul><li>Some are common decomposers of cellulose in soil </li></ul><ul><li>(e.g. Chaetomium species) </li></ul><ul><li>They are the least specialised of the wood-rot fungi </li></ul>Figure 3. Soft rot of wood University of Minnesota (2006)
    5. 5. Brown-rot fungi <ul><li>Degrade the cellulose and hemicellulose </li></ul><ul><li>leave the lignin intact as a brown framework </li></ul><ul><li>6% of wood-decay fungi cause brown rots </li></ul><ul><li>All these fungi are members of the basidiomycota. They include dry-rot fungus </li></ul><ul><li>(Serpula lacrymans) and brown cubical rot of birch (Piptoporus betulinus) </li></ul>Figure 2. Brown rot in wood Australian Government (2006)
    6. 6. White-rot fungi <ul><li>These fungi degrade all major wood components (cellulose, hemicelluloses and lignin) </li></ul><ul><li>Wood becomes more fragile but remains white as it decays. </li></ul><ul><li>Caused by the two major root-rot pathogens of trees, the honey fungus </li></ul><ul><li>(Armillaria mellea ) and butt rot ( Heterobasidion annosum) , and also by many saprotrophic fungi, including turkey tail mushroom ( Coriolus versicolor). </li></ul>Figure 1. White rot in wood. Doe Joint genome insitute (2006)
    7. 7. Type of decay <ul><li>Wood rotting fungi are defined as; </li></ul><ul><li>“ those which can bring about significant weight lass and structural change in woody tissues”. </li></ul><ul><li>There are 3 types of wood decay each taking its name from the general appearance of the decayed wood. They are known as; </li></ul><ul><li>Brown rot </li></ul><ul><li>White rot </li></ul><ul><li>Soft rot </li></ul>
    8. 8. Type of decay Brown Rot only cellulose and other wood carbohydrates are utilized so the wood remains predominantly brown in colour . Fragile, powdery, brown cracks and clefts Consistency Drastic reduction of bending and impact strength Strength Cellulose and hemicellulose degradation Degradation Basidiomycetes -especially from the family of the Polyporaceae Fungi Especially in coniferous trees Host fungi
    9. 9. Type of decay White Rot Oxidation of lignin causes the wood to take on a white or bleached appearance. Ductile fracture. At the initial stage: slight increase in impact bending strength Brittle fracture. At the initial stage: great reduction of impact bending strength Strength Fibrous (stringy) Brittle Consistency First lignin and hemicellulose, later cellulose also Cellulose, lignin and hemicellulose Degradation Basidiomycetes and Ascomycetes Fungi Broad-leaved trees and conifers but seldom in conifers Broad-leaved trees Host Selective delignification Simultaneous rot
    10. 10. Type of decay Soft Rot Wood loses mechanical strength and becomes wet and spongy. Between brown and white rot High stiffness Brittle fracture Strength Brittle Consistency Cellulose and hemicellulose. Lignin strongly. Cellulose and hemicellulose. Lignin slightly. Degradation Basidiomycetes Deuteromycetes & Ascomycetes Fungi Extensive decay in living broad-leaved trees. Broad-leaved trees and conifers. Especially on wooden structures. Host New information Conventional picture
    11. 11. Fungal succession in decay of wood
    12. 12. Fungal succession in decay of wood
    13. 13. Fungal succession in decay of wood
    14. 14. Method by which soft-rot fungi breakdown wood <ul><li>Pectolytic enzymes produced, breaking down pectic acid, leading to partial degradation of cell wall </li></ul><ul><li>Degradation of wall leads to cell secretions of nutrients, explaining appearance </li></ul><ul><li>Hyphae then penetrate in the cell, growing broader, releasing cellulase enzymes </li></ul><ul><li>This causes generalized decay of cellulose in a rhomboidal shape </li></ul>
    15. 15. Method by which brown-rot fungi breakdown wood <ul><li>Cellulase enzymes created by fungi, have little impact on the cellulose </li></ul><ul><li>Breakdown relies on weaker hemicelluloses. This breakdown is actually an oxidation process in which hydrogen peroxide is formed. </li></ul><ul><li>Hydrogen peroxide is strong oxidiser and readily causes generalized decay, of cellulose </li></ul><ul><li>Leaves the lignin intact, maintaining the general cell shape </li></ul>
    16. 16. Method by which white-rot fungi breakdown wood <ul><li>White rot capable of breaking down all major components of the wood. </li></ul><ul><li>The fungi use conventional cellulase enzymes to breakdown hemicelluloses and cellulose, exposing lignin. </li></ul><ul><li>The lignin is complex polymer but the fungi only require a few enzymes to break it down. </li></ul><ul><li>Again an example of an oxidation process with strong oxidisers such as hydrogen peroxide, lignin peroxidase and laccase. </li></ul><ul><li>The resultant molecules can become fungi toxic to the fungi so it detoxifies it by polymerisation. </li></ul>
    17. 17. Conclusion
    18. 18. References <ul><li>Australian Government, Department of the Environment and Heritage. (2006). Brown rot in wood. [Online] URL: http://www.anbg.gov.au/fungi/images-captions/brown-rot-wood-0121.html </li></ul><ul><li>Site accessed 19/01/2007 </li></ul><ul><li>Blanket, R. 2006. Soft Rot </li></ul><ul><li>http://forestpathology.coafes.umn.edu/archaeologicalwood.htm </li></ul><ul><li>Site accessed 19/01/2007 </li></ul><ul><li>Brown rot jpg. 2007. </li></ul><ul><li>http://webs.wichita.edu/mschneegurt/biol103/lecture21/Brown_rot.gif </li></ul><ul><li>Site accessed 19/01/2007 </li></ul><ul><li>Deacon. J. (1997). The Microbial World: Armillaria mellea and other wood-decay fungi. [Online] URL: http://helios.bto.ed.ac.uk/bto/microbes/armill.htm </li></ul><ul><li>Deacon, J. 2006. Fungal biology. (Fourth edition). Blackwell Publishing. pp 217-235 </li></ul><ul><li>Dix, N. J. & Webster, J. 1995. Fungal Ecology. Chapman & Hall, London. P. 161 </li></ul><ul><li>Doe Joint Genome Institute. (2006). Why sequence white rot fungus?. [Online] URL: http://www.jgi.doe.gov/sequencing/why/whiterot.html </li></ul><ul><li>Ingold, C., & Hudson, H. 1993. The biology of fungi. (Sixth Edition). Chapman and Hall publishers. Pp146-160 </li></ul>
    19. 19. References <ul><li>Schwarze, F. W. M. R., Engels, J. & Mattheck, C. 2000. Fungal Strategies of Wood Decay In Trees. Springer, New York. pp. 185 </li></ul><ul><li>University of Minnesota. (2006). Microbes in trees and wood. [Online] URL: http://forestpathology.coafes.umn.edu/microbes.htm </li></ul><ul><li>World of fungi. 2007 </li></ul><ul><li>http://www.world-of-fungi.org/Mostly_Mycology/Lucy_Goodeve-Docker_bioremediation_website/whiterotfungi.htm </li></ul><ul><li>Site accessed 17/01/01 </li></ul>

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