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Chapter 12

Fungal interactions: mechanisms

and practical exploitation

This chapter is divided into the following major sections:

• the terminology of species interactions


• antibiotics and their roles in species interactions


• antibiotics and disease control by Trichoderma
  species


• hyphal interference: a classic example of applied bio-
  logical control


• mycoparasites: fungi that parasitize other fungi


• competitive interactions among fungi


• commensalism and mutualism among fungi

Microorganisms interact in many diverse ways. In this

chapter we consider some of the major types of inter-

action involving fungi, and the potential for exploiting

these interactions for practical benefit. We will also

discuss the use of several commercially available

biological control agents. (See Online resources for this

chapter.)

The terminology of species interactions

The terminology of species interactions is difficult,
but for most purposes we can distinguish three broad
categories of interaction among fungi:

1 The ability of one species to exclude another by
competition(sometimes called exploitation com-
petition), i.e. by being faster or more efficient in
exploiting a resource (space, substrate, etc.).
2 The ability of one species to exclude or replace
another by antagonism(sometimes called inter-

ference competitionor combat), i.e. by directly

affecting another organism through antibiotic pro-

duction, parasitism, etc.

3 The ability of two species to coexist (commensalism)

to the benefit of one or both (mutualism).

It must be emphasized that these types of interaction

grade into one another, because fungi can behave dif-

ferently in different situations.

Antibiotics and their roles in species

interactions

An antibiotic can be defined somewhat arbitrarily as a

diffusible secondary metabolite of one (micro)organism

that inhibits another (micro)organism at a concentra-

tion of 100μgml−^1 or less. This definition serves to

exclude general metabolic byproducts such as CO 2 or

organic acids. It restricts the term to specific highly

active compounds that affect specific cellular targets.

The best-known antibiotics from fungi are the peni-

cillins(Chapter 7), cephalosporins,and griseofulvin

(Chapter 15), which are used clinically to control bac-

teria or, in the case of griseofulvin, other fungi. Some

more recently discovered antibiotics include fusidic acid

from the mitosporic fungus Fusidium coccineum, which

is active against Gram-positive bacteria, fumagillin

from Aspergillus fumigatus, which is used to control par-

asitic protozoa in veterinary medicine, and sordarin,

from a species of Sordaria(Ascomycota) to control fun-

gal infections of humans.

These are only a few of the 1000 or more antibiotics

known to be produced by fungi. Most of the antibiotics

discovered in routine screens by chemical companies