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Chapter 6

Fungal nutrition

This chapter is divided into the following major sections:

• the basic nutrient requirements of fungi


• carbon and energy sources of fungi


• fungal adaptations for nutrient capture


• the breakdown of cellulose: a case study of extra-
  cellular enzymes


• mineral nutrient requirements: nitrogen, phosphorus,
  and iron


• efficiency of substrate utilization


• fungi that cannot be cultured

Fungi have quite simple nutritional requirements.

They need a source of organic nutrients to supply their

energy and to supply carbon skeletons for cellular

synthesis. But, given a simple energy source such as

glucose, many fungi can synthesize all their other cel-

lular components from inorganic sources – ammonium

or nitrate ions, phosphate ions and trace levels of other

minerals such as calcium, potassium, magnesium, and

iron. Fungi that normally grow in a host environment

or in other nutrient-rich substrates might require

additional components, but still the nutrient require-

ments of most fungi are quite simple.

Having said this, fungi need to capture nutrients from

their surroundings. The cell wall prevents fungi from

engulfing food particles, so fungi absorb simple, sol-

uble nutrients through the wall and plasma membrane.

In many cases this is achieved by releasing enzymes

to degrade complex polymers and then absorbing the

nutrients released by these depolymeraseenzymes.

Fungi produce a huge range of these enzymes, to

degrade different types of polymer. In fact, there is

hardly any naturally occurring organic compound that

cannot be utilized as a nutrient source by one fungus

or another.

In this chapter we consider the many adaptations

that fungi have evolved for nutrient capture.

The nutrient requirements of fungi

For routine laboratory culture, most fungi are grown

on media with natural components, such as potato-

dextrose agar(extract of boiled potatoes, with 2% w/v

glucose), malt extract agar(usually containing 2% malt

extract), or cornmeal (or oatmeal) agar– a culture

medium often used to promote sexual development.

Fungal growth media are usually slightly acidic (pH 5 – 6)

and rich in carbohydrates. This contrasts with bacterial

culture media such as “nutrient agar” (beef extract and

peptone) which are usually neutral or alkaline (pH 7– 8)

and rich in organic nitrogen. This difference reflects the

higher gross protein content of bacteria compared with

fungi. Other types of agar are used to culture specific

fungi or to promote specific developmental stages.

However, in order to determine the minimum

nutrient requirements, a fungus must be grown in

chemically defined liquid culture, because agar contains

impurities. Table 6.1 shows a typical minimal medium,

containing only mineral salts and glucose. Several

common fungi will grow on this medium. The main

exceptions are noted below.

• Some fungi need to be supplied with one or more
  vitamins, the most common requirements being for
  small amounts of thiamine, biotin, or both.