Escuela de Lenguas UNLP/Academic Writing/Biology/Wood-rotting fungi

Wood-rotting fungi

Fungi are particularly important as agents of decomposition in terrestrial and aquatic environments. They can degrade woody substrate which contains cellulose, hemicellulose and lignin, and many other natural or anthropogenic materials. Saprotrophic fungi are classified into three groups according to their mode of attack on the woody cell wall: soft-rot fungi, brown-rot fungi and white-rot fungi.

Soft-rot fungi (SRF): They grow on wood, producing superficial damage. Their hiphae penetrate the thin lignin layer and access to the cellulose-rich layer, which is enzymatically degraded. The diffusion of these enzymes produces rhomboidal cavities leaving a characteristic pattern of decay. The wood loses resistance and turns into damp and porous. Several Ascomycota and mitosporic species, such as Chaetomiun globosum and Daldinia concentrica (Moore-Landecker, 1996) cause soft rot.

Brown-rot fungi (BRF): They are mainly Basidiomycota, including common species such as Schizophyllum commune, Fomes fomentarius, Serpula lacryman and Gloephyllum trabeum. They degrade hemicellulose and cellulose, leaving the lignin more o less intact as a brown decaying wood, which is the reason for the name “brown-rot”. Brown-rot fungi degrade cellulose by a diffusable cellulolytic system, involving the production of hydrogen peroxide and manganese ions.

White-rot fungi (WRF): They are more numerous than brown-rot fungi, and are represented in all the main group of Basidiomycota (Agaricomycotina) and in some of the Ascomycota namely the Xylariaceae. The main feature of WRF is their ability to degrade lignin by extracellular oxidative enzymes (lignin peroxidase, manganese peroxidase and laccase). The term “white rot” is used to describe the bleached appearance of the wood. The wood takes on a spongy, stringy or laminated structure where lignin, cellulose and hemicellulose are degraded. Interestingly, lignin is broken down to obtain cellulose as a carbon source for growth (Anastasi et. al., 2013). They are able to use nitrogen efficiently. WRF include species such as Phanaerochaete chrysosporium, Pleurotus ostreatus, Trametes versicolor, Coriolus versicolor, Irpex lacteus and Xylaria hypoxylon.

Bioremediation using wood-rotting fungi

The decontamination of soil and water from pollutants using microorganisms (bacteria, fungi or plants) is known as bioremediation. Wood-rotting fungi, speciality white-rot fungi, have potential for bioremediation of land contaminated by persistent xenobiotic pollutants. It has been estimated that some 30% of the literature on fungal bioremediation is concerned with WRF. The main reason why WRF can degrade a wide range of compounds is their release of extracellular lignin-modifying enzymes. These enzymes can act upon various molecules that are broadly similar to lignin. The white- rot fungus Phanerochaete chrysosporium is an ideal model for mycoremediation (bioremediation by fungi), since it is more efficient than other fungi or microorganisms in degrading toxic or insoluble materials. As several studies have demonstrated, WRF are a promising tool for bioremediation. However, more research must be performed in order to improve full-scale application.

Bibliography:

• Anastasi, A., V. Tigini and G. C. Varese. 2013. Chapter 2: The Bioremediation Potential of Different Ecophysiological Groups of Fungi. Pp 29-49. In: Goltapeh, E.M. et al. (Eds.). Fungi as Bioremediators, Soil Biology 32. Springer Science & Business Media. Berlin.
• Baldrian, P. 2008. Wood-inhabiting ligninolytic basidiomycetes in soils: Ecology and constraints for applicability in bioremediation. Fungal ecology I (2008) 4–12. doi:10.1016/j.funeco.2008.02.001
• Deacon, J. W. 2006. Fungal biology. 4th ed. Blackwell Publishing. Edinburgh, UK. 384 pages.
• Gadd, G. M. 2001. Fungi in Bioremediation. Cambridge University Press. Cambridge, UK. 24 pages.
• Moore-Landecker, E. 1996. Fundamentals of the Fungi. 4th ed. Benjamin-Cummings Pub Co. 574 pages.
• Pointing SB, 2001. Feasibility of bioremediation by white-rot fungi. Applied Microbiology and Biotechnology 57: 20–33.
• Rhodes, C. J. 2014. Mycoremediation (bioremediation with fungi) – growing mushrooms to clean the earth. Chemical Speciation & Bioavailability. 26:3. 196-198. DOI: 10.3184/095422914X14047407349335
• Singh, H. 2006. Mycoremediation: fungal bioremediation. Wiley, Hoboken. 592 pages. ISBN: 978-0-471-75501-2