Common saprophytic fungi include brown rots such as Laetiporus and Phaeolus, white rots such as Pleurotus and Trametes, and litter decomposers such as Agaricus and Agrocybe. These fungi have one important fact in common. They decompose dead plants, the bulk of which is plant cell wall material. Cellulose and lignin make up plant cell walls, and are the two most abundant organic compounds on earth. Cellulose is a relatively simple polysaccharide, and even though very few animals have the enzymes to digest it, saprophytic fungi do, and have been using cellulose as an abundant food source for hundreds of millions of years. Lignin presents an entirely different set of problems for decomposers. It is a complex polyphenolic compound, having evolved in part precisely to protect plant cells from the ravages of fungal and insect attack. The complex mechanisms and enzymes employed by lignin-digesting fungi are finally beginning to be elucidated, and they are revealing some intriguing connections. Could fungal bioluminescence be tied to the process of lignin decomposition by white rot fungi? Could the synthesis of polyphenolic compounds of plants, animals and fungi be related to their protective, toxic, and/or medicinal potentials?
