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CHAPTER 7: FUNGAL
METABOLISM AND FUNGAL PRODUCTS
This chapter is divided into the
following major sections:
how fungi obtain
energy in different environmental
conditions
co-ordination of metabolism: how the
pathways are balanced
the mobilisable and storage compounds of
fungi
the synthesis of chitin and lysine
the pathways and products of secondary
metabolism
Sample text:
In this
chapter we discuss the basic metabolic pathways of fungi,
as a basis for understanding how fungi grow on different
types of substrate and in different environmental
conditions. We also cover some of the distinctive and
unusual aspects of fungal metabolism, including the
production of a wide range of secondary metabolites of
commercial and environmental significance, such as the penicillin
antibiotics and important mycotoxins like the highly
carcinogenic aflatoxins and the toxic ergot
alkaloids. Some of the material in this chapter will
be familiar, basic biochemistry. But it is presented in
the specific context of fungal biology.
Chapter 7 images. Click on
the thumbnails
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Fig. 7.1
Fig. 7.6
Fig. 7.10
Fig. 7.13
Fig. 7.20a
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Fig. 7. 2
Fig. 7.7
Fig. 7.14
Fig. 7.15
Fig. 7.20b
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Fig. 7.3
Fig. 7.4
Fig. 7.8
Fig. 7.11
Fig. 7.16
Fig. 7.17
Fig. 7.20c
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Fig. 7.5
Fig. 7.9
Fig. 7.12
Fig. 7.18
Fig. 7.19
Fig. 7.20d
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| Table 7.1. Some secondary
metabolites derived from different pathways and
precursors |
| Precursor |
Pathway |
Metabolites;
representative organisms |
| Sugars |
|
Few, e.g. muscarine
(Amanita muscaria)
kojic acid (Aspergillus spp.) |
| Aromatic amino acids |
Shikimic acid |
Some lichen acids |
| Aliphatic amino acids |
Various, including
peptide synthesis |
Penicillins (P.
chrysogenum, P. notatum)
Fusaric acid (Fusarium spp.)
Ergot alkaloids (Claviceps, Neotyphodium)
Lysergic acid (Claviceps purpurea)
Sporidesmin (Pithomyces chartarum)
Beauvericin (Beauveria bassiana)
Destruxins (Metarhizium anisopliae) |
| Organic acids |
TCA cycle |
Rubratoxin (Penicillium
rubrum)
Itaconic acid (Aspergillus spp.) |
| Fatty acids |
Lipid metabolism |
Polyacetylenes
(Basidiomycota fruitbodies and hyphae) |
| Acetyl-CoA |
Polyketide |
Patulin (Penicillium
patulum)
Usnic acid (many lichens)
Ochratoxins (Aspergillus ochraceus)
Griseofulvin (Penicillium griseofulvum)
Aflatoxins (A. parasiticus, A.
flavus) |
| Acetyl Co-A |
Isoprenoid |
Trichothecenes (Fusarium
spp.)
Fusicoccin (Fusicoccum amygdali)
Several sex hormones: sirenin, trisporic
acids, oogoniol, antheridiol
Cephalosporins (Cephalosporium and
related fungi)
Viridin (Trichoderma virens) |
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Table 7.2. Some representative
mycotoxins in foodstuffs
|
Toxin
|
Representative fungi
|
Foodstuff
|
Effects
|
| Aflatoxins |
Aspergillus
flavus
A. parasiticus
|
Peanuts, oilseeds |
Nephrotoxic,
hepatocarcinomas |
| Ergot alkaloids |
Claviceps
purpurea
|
Cereals, grasses |
Neurotoxic |
| Fuminosins |
Fusarium
moniliforme |
Maize |
Human oesophageal
cancer in Africa?
|
| Ochratoxin A |
Some Aspergillus
and
Penicillium spp.
|
Grain crops |
Nephrotoxic, kidney
carcinoma |
| Patulin |
Penicillium
expansum,
Aspergillus clavatus
|
Apples |
Contact oedema,
haemorrhage |
| Sporidesmin |
Pithomyces
chartarum |
Grass |
Facial eczema of
sheep, cattle
|
| Sterigmatocystin |
Aspergillus spp.
|
Grain, oilseeds |
Hepatocarcinogen |
| Trichothecenes |
Fusarium spp.
Stachybotrys chartarum
|
Cereals |
Abortive,
blistering, oestrogenic |
| Zearalenone |
Fusarium
|
Cereals |
Vulvovaginitis |
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