Chapter 1
Introduction: the fungi and
fungal activities
This chapter is divided into the following major sections:- the place of fungi in the “Tree of Life” – setting the
scene - the characteristic features of fungi: defining the fun-
gal kingdom - the major activities of fungi as parasites, symbionts
and saprotrophs - fungi in biotechnology
Fungi are a unique group of organisms, different from
all others in their behavior and cellular organization.
Fungi also have an enormous range of activities – as
pathogens of crop plants or humans, as decomposer
organisms, as experimental “model organisms” for
investigating genetics and cell biology, and as producers
of many important metabolites. The uniqueness of fungi
is a prominent feature of this book, which adopts a
functional approach, focusing on topics of inherent
interest and broad significance in fungal biology.
The uniqueness of fungi is reflected in the fact that
they have the status of a kingdom, equivalent to the
plant and animal kingdoms. So, fungi represent one of
the three major evolutionary branches of multicellular
organisms.
In terms of biodiversity, there are estimated to
be at least 1.5 million different species of fungi, but
only about 75,000 species (5% of the total) have been
described to date. For comparison, there are estimated
to be 4.9 million arthropod species and about 420,
seed plants (Hawksworth 2001, 2002).
If the estimate of the number of fungal species is
even remotely accurate then we still have much to learn,
because even the fungi that we know about playmany important roles. To set the scene, we can men-
tion just a few examples:- Fungi are the most important causes of crop dis-
eases, responsible for billions of dollars worth of
damage each year, and for periodic devastating
disease epidemics. - Fungi are the main decomposersand recyclers of
organic matter, including the degradation of cellu-
lose and wood by the specialized enzyme systems
unique to fungi. - Fungi produce some of the most toxic known
metabolites, including the carcinogenic aflatoxins
and othermycotoxinsin human foods and animal
feedstuffs. - With the advance of the acquired immune
deficiency syndrome (AIDS) and the increasing role
of transplant surgery, fungi are becoming one of
the most significant causes of death ofimmuno-
compromised andimmunosuppressed patients.
Fungal diseases that were once extremely rare are
now commonplace in this sector of the population. - Fungi have an enormous range of biochemical
activitiesthat are exploited commercially – notably
the production of antibiotics (e.g. penicillins),
steroids(for contraceptives), ciclosporins(used as
immunosuppressants in transplant surgery), and
enzymes for food processing and for the soft drinks
industry. - Fungi are major sources of food. They are used
for bread-making, for mushroom production, in sev-
eral traditional fermented foods, for the production
of Quorn™mycoprotein – now widely available in
supermarkets and the only survivor of the many
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