gom1

Useful fungi
29
A key question is: Why do fungi make medicines that are so
beneficial to humans? Fungi live in competitive environments
and they cannot easily move to new niches when competition
for resources is high. They therefore need to defend their
patch, and one means of fighting off competitor fungi or
bacteria is the production of antibiotics. The majority of
the fungal chemical compounds in Figure 3 are antibiotics
that inhibit the growth of either bacteria or fungi. Even the
immunosuppressant drugs cyclosporine, mycophenolic acid
and myriocin (which are not used as antibiotics) display
potent antifungal activity [21–23] , as does the statin drug
lovastatin [24] . This suggests that the role of these chemical
compounds in nature is to protect the fungi that produce
them from microbial competitors, and this role is exploited
by humans – we benefit from the fundamental biochemical
similarities between fungi and humans. This also explains
why antifungal chemical compounds such as statins have
unintended benefits in human medicine [25,26] . Similarly,
biochemical pathways that control activation of immune cells
in humans are also present in fungi [27–29] .
Humans can also benefit from compounds that are
produced by fungi to enable them to invade the bodies of
other organisms. Cyclosporine and myriocin, both of which
act as immunosuppressants in humans, are produced by
fungal species that are able to invade insects’ bodies.
The fungus Tolypocladium inflatum, which produces
cyclosporine, is able to infect beetle larvae – an infected
larva actually becomes the base of the fungus from which
the spore-bearing structure emerges [30] . Similarly, the fungus
Isaria sinclairii, which produces myriocin, infects cicada
larvae [31] (see Box 1). It has been suggested that for these
fungi to survive inside insect larvae, they must produce
immunosuppressant chemical compounds to evade the
host’s immune system. Experiments with insect larvae
models do indeed show that cyclosporine and myriocin cause
immunosuppression in insect larvae [32,33] . This example
demonstrates the importance to drug discovery of tapping
into new and unusual sources of fungi, such as those that
live inside insects and plants [34,35] .
APPLICATIONS OF FUNGAL ENZYMES
Enzymes are natural molecules that catalyse
(cause or speed up) chemical reactions.
A particularly important use of enzymes is
in industry, where they are changing the way
industrial chemical processes are conducted. Industrial
processes that would normally require high temperatures
or harsh chemicals can be carried out under far milder
conditions using enzymes [36] and fungi have proved a useful
source: 60% of the enzymes used in industry come from
fungi and 70% of these are derived from just seven fungal
species (see Figure 4).
In natural environments, fungi produce efficient
cellulase enzymes to break down wood and leaves into
digestible components and this makes them ideal for paper
manufacturing, where wood needs to be broken down into
a soft pulp. Cellulase enzymes produced by species of
Trichoderma and Humicola are used to speed up the
pulping process thereby reducing water usage [37,38] .
FIGURE 2: THE MAJOR GENERA OF CULTIVATED
EDIBLE MUSHROOMS
85% of cultivated edible mushrooms come from just five
genera: Lentinula (A), Pleurotus (B), Auricularia (C), Agaricus
(D) and Flammulina (E)
A
B
C
D
E