21st Century Guidebook to Fungi

Fungi make crucial contributions to all ecosystems because of their abilities as decomposers. One of the most important kingdom-specific characteristic of fungi is that they obtain their nutrients by external digestion of substrates. In the real world, though there is some digestion of inorganic substrates (see Section 1.7), the bulk of the substrates that fungi recycle are the remains of animals and, most particularly, plants. In this chapter we give an account of the ways in which fungal hyphae obtain, absorb, metabolise, reprocess and redistribute nutrients.

In doing this, fungi obviously contribute to recycling and mineralisation of nutrients and in what follows we will describe the enzyme systems that enable this activity. Our description is relatively brief and more details can be found in the premier text on fungal physiology (Jennings, 2008). For clarity we have to describe separately the enzyme systems involved, and in an order that we have chosen for descriptive purposes. This introduction is intended to convey the impression that for most fungi in most circumstances the initial nutritional step is the excretion of enzymes able to convert polymers to the simple sugars, amino acids, carboxylic acids, purines, pyrimidines, etc., that the cell can absorb. Also, in most circumstances most fungal mycelia will be carrying out all of these biochemical changes simultaneously.