White rot fungi produce unique extracellular oxidative enzymes that degrade lignin, as well as related compounds found in explosive contaminated materials, pesticides, and toxic wastes. To elucidate the genetic basis of this technologically important behavior, we have sequenced the thirty million base-pair genome of the white rot fungus Phanerochaete chrysosporium to high draft using a whole genome shotgun method. This is the first basidiomycete genome to be sequenced.
Lignin plays a key role in the carbon cycle as the most abundant aromatic compound in nature, providing the protective matrix surrounding the cellulose microfibrils of plant cell walls. This amorphous and insoluble polymer lacks stereoregularity and, in contrast to cellulose and hemicellulose, it is not susceptible to hydrolytic attack. Although lignin is a formidable substrate, its degradation by certain fungi was recognized and described nearly 125 years ago. Collectively referred to as white rot fungi (since they degrade brown lignin, and leave behind white cellulose), these are the only microbes capable of efficient depolymerization and mineralization of lignin. All are basidiomycetes, a fungal group that includes both edible mushrooms as well as plant pathogens such as smuts and rust.
Phanerochaete chrysosporium has been the most intensively studied white rot fungus. White rot fungi secrete an array of peroxidases and oxidases that act non-specifically via the generation of lignin free radicals, which then undergo spontaneous cleavage reactions. The non-specific nature and exceptional oxidation potential of the enzymes has attracted considerable interest for application in bioprocesses such as organopollutant degradation and fiber bleaching.
Phanerochaete chrysosporium has several features that might make it very useful. First, unlike some white rot fungi, it leaves the cellulose of the wood virtually untouched. Second, it has a very high optimum temperature (about 40 °C), which means it can grow on wood chips in compost piles, which attain a very high temperature. These characteristics point to some possible roles in biotechnology.
- Computational analysis of the Phanerochaete chrysosporium v2.0 genome database and mass spectrometry identification of peptides in ligninolytic cultures reveal complex mixtures of secreted proteins. Vanden Wymelenberg A, Minges P, Sabat G, Martinez D, Aerts A, Salamov A, Grigoriev I, Shapiro H, Putnam N, Belinky P, Dosoretz C, Gaskell J, Kersten P, Cullen D. Fungal Genetics and Biology - Volume 43, Issue 5, May 2006, Pages 343-356 [doi:10.1016/j.fgb.2006.01.003]
- The Phanerochaete chrysosporium secretome: database predictions and initial mass spectrometry peptide identifications in cellulose-grown medium. Wymelenberg AV, Sabat G, Martinez D, Rajangam AS, Teeri TT, Gaskell J, Kersten PJ, Cullen D. Journal of Biotechnology - Volume 118, Issue 1, 2 July 2005, Pages 17-34 [DOI:10.1016/j.jbiotec.2005.03.01]
- Genome sequence of the lignocellulose degrading fungus Phanerochaete chrysosporium strain RP78. Martinez D, Larrondo LF, Putnam N, Gelpke MD, Huang K, Chapman J, Helfenbein KG, Ramaiya P, Detter JC, Larimer F, Coutinho PM, Henrissat B, Berka R, Cullen D, Rokhsar D. Nature Biotechnology 22, 695 - 700 (2004) [DOI: 10.1038/nbt967]