ABSTRACT
The mycelium of mushrooms, like all fungal cells, lacks chlorophyll and consequently is unable to utilize carbon dioxide, mineral ions, and water for photosynthesis as do green plants. Nutritionally, mushrooms are heterotrophs and obtain their nutrients by absorbing soluble inorganic and organic materials from substrates such as wood logs, manure composts, or other organic synthetic composts. Recall that in Chapter 4 we referred to this as absorptive or osmotrophic nutrition and mentioned the role of extracellular enzymes in breaking down insoluble compounds such as polysaccharides into smaller, soluble substances. Once organic compounds have entered the fungal cell, they can be converted to the various sugars, polysaccharides, proteins, lipids, purines, pyrimidines, vitamins, etc. required for the vital activities and structural needs of the fungus. The fungi are endowed with exceptional metabolic capabilities; many of them are able to grow and reproduce when supplied with a sugar as carbon source, a nitrogen source, various minerals, possibly a vitamin, and water. The carbon source provides the skeletal carbon for organic compounds and the energy for the anabolic processes. The nitrogen is essential for amino acids and, therefore, for proteins and enzymes. The minerals such as phosphorus, sulfur, magnesium, and potassium have a variety of functions, and the vitamins function as coenzymes.
