Phanerochaete chrysosporium

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A Microbial Biorealm page on the genus Phanerochaete chrysosporium

Classification

Higher order taxa

Eukaryota; Fungi/Metazoa group; Fungi; Dikarya; Basidiomycota; Agaricomycotina; Agaricomycetes; Agaricomycetes incertae sedis; Corticiales; Corticiaceae; Phanerochaete

Species

NCBI: Taxonomy

Phanerochaete chrysosporium

Description and significance

Phanerochaete chrysosporium is the model white rot fungus because of its specialized ability to degrade the abundant aromatic polymer lignin, while leaving the white cellulose nearly untouched. Phanerochaete chrysosporium releases extracellular enzymes to break-up the complex three-dimensional structure of lignin into components that can be utilized by its metabolism. The extracellular enzymes are non-specific oxidizing agents (hydrogen peroxide, hydroxyl radicals) used to cleave the lignin bonds. [3]

Due to Phanerochaete chrysoporium specialized degradation abilities, extensive research is seeking ways to understand the mechanism in order to enhance the bioremediation of a diverse range of pollutants. Therefore, Phanerochaete chrysosporium is the first member of the Basidiomycetes to have its complete genome sequenced. [6]

Genome structure

Phanerochaete chrysoporium's genome consists of approximately 29.6-million base pairs arranged in ten linear chromosomes [6]. Genomic analysis provides structural, comparative, and functional information about the organisms.

P. chrysoporium’s importance in the field of biotechnology lead to the analysis P450 monooxygenase genes to provide information about the complex protein interactions and distinct components involved in the production of the polyaromatic degrading extracellular enzyme. In the P450 genes, microexons were detected to suggest the mechanisms of alternative splicing during transcription, which may explain this organism’s evolution of diverse metabolic activity. [7]

Cell structure and metabolism

Phanerochaete chrysosporium is a crust fungi, which forms flat fused reproductive fruiting bodies instead of the mushroom structure. This fungi exhibit an interesting pattern of septate hyphae, giving a stronger line of defense in times of distress. The hyphae network has some branching, with diameters ranging from 3-9 µm. At the ends of the hyphae rests chlamydospores, thick-walled spores varying from 50-60 µm. The conidiophore gives rise to round asexual blastoconidia, which are 6-9 µm in diameter. [1,2]

Degradation of lignin and polutants is made possible by the production of extracellular enzymes. Components such as lignin peroxidase and manganese peroxidase take part in the remediation of various pesticides, polyaromatic hydrocarbons, PCBs, TNT, carbon tetrachloride and various poisons. [8]

Metabolism of Lignin

Reseach in the degradation of lignin has resulted in numerous substituted benzene ring products. An important catalyst in these reactions are phenol-oxidizing enzymes. [9]

The process of lignin breakdown is carried out by means of cleavage reactions. These extracellular enzymes release free-radicals to initiate spontaneious break down to phenyl propane units in the Secondary metablism or stationary phase. [8]

Ecology

Due to Phanerochaete chrysosporium sustainability at moderate to higher temperatures, specifically 40 degrees celcius, this white-rot fungus can be found in forests ranging from North America, to areas of Europe and in Iran. [4] A main role it assumes is that of degradation of the complex lignin from various trees and plants. This process reduces lignin into less complex molecules, maintaining the cycle of the decomposer of plants.

Recent studies have revealed an association of a certain bacteria found in conjunction with this strain of fungi. Agrobacterium radiobacter was isolated as coexisting with the fungi, and very difficult to separate. [5] Discovery of how bacteria and fungi affect each other physiologically is yet to be conclusive, but further research could give further evidence of mutualism, and its affect on bioremdiation.

Pathology

Phanerochaete chrysosporium is a saprophytic fungus capable of organic breakdown of the woody part of dead plants. Therefore, plants that are in the process of dieing or dead serve as an optimal substrate for P. chrysosporium. Symptoms may include white patches of cellulose due to the disappearance of lignin from the plant structure.

This fungus is not a known pathogen of humans or animals.

Application to Biotechnology

Not only is Phanerochaete chrysosporium useful because of its biodegradation of harmful chemicals by means of extracellular enzymes, its ability to leave pure white cellulose has been important in the industry of paper. Biopulping would cut out the use of machines to remove brown lignin, which this fungi does naturally, all the while bleaching the cellulose left behind that goes into the mass production of paper. Incorporation of this natural alternative would limit the amount of pollution produced by machines previously designed for this very job, and also decrease the amount of chemicals used for the bleaching of paper. [11] Some limitations to the use of P. chrysosporium in the biopulping industry include the fact that pulp is a relatively low value product and aerating the fungi may be expensive, many fungi have low growth rates, and large wood chips are resistant to diffusion [12].

Current Research

Finding a way to degrade everyday plastics has been a concern for sometime now. Research has shown Phanerochaete chrysosporium to be a degrader of phenolic resins found in such plastics within particle board and Formica, the constitutent of many counters and table tops. Research ensues as other types of fungi are found to be inclined to degrade complex components of plastic. Tom Volk's Fungus of the Month for February 2007

References

1. Burdsall, H. (1985) Mycologia Memoir 10, 61-63.
2. Nakasone, K. (1990) Mycologia Memoir 15, 224-225.
3. Burdsall, H. (1974) Mycotaxon 1, 124.
4. Burdsall, H. (1985) Mycologia Memoir 10, 61-63
5. F. Seigle-Murandi, P. Guiraud, J. Croize, E. Falsen, and K. L. Eriksson, "Bacteria Are Omnipresent on Phanerochaete chrysosporium Burdsall." "Applied and Environmental Microbiology Journal." 1996 July; 62(7): p.2477–2481.
6. Martinez D et al., "Genome sequence of the lignocellulose degrading fungus Phanerochaete chrysosporium strain RP78.", Nat Biotechnol, 2004 Jun;22(6):695-700
7. Doddapaneni, Harshavardhan, Ranajit Chakraborty, and Jagjit Yadav. "Genome-Wide Structural and Evolutionary Analysis of the P450 Monooxygenase Genes (P450ome) in the White Rot Fungus Phanerochaete Chrysosporium : Evidence for Gene Duplications and Extensive Gene Clustering." BMC Genomics 6 (2005). 9 Mar. 2008.
8. Scow, Kate. "Lecture 6: Carbon Cycle." Winter, 2008.
9. Toshiaki Umezawa1, Fumiaki Nakatsubo1, and Takayoshi Higuchi1. "Lignin degradation byPhanerochaete chrysosporium: Metabolism of a phenolic phenylcoumaran substructure model compound." Archives of Microbiology, 131(2): March 1982.
10. Hammel, Kenneth E. "Mechanisms for Polycyclic Aromatic Hydrocarbon Degradation by Ligninolytic Fungi." Environmental Health Perspectives 103 (1995). 9 Mar. 2008.
11. Blanchette, Robert A., Todd A. Burns. "Selection of White-Rot Fungi for Biopulping." Department of Plant Pathology, University of Minnesota. Nov. 1987.
12. Kirk, K.T., Richard R. Burgess, and John W. Koning, Jr. "Use of Fungi in Pulping Wood: An Overview of Biopulping Research." Frontier Proceedings of Industrial Mycology symposium, Madison, WI. New York: Routledge, Chapman & Hall, 1992.