9.5 Bioactive Metabolites from Endophytic Fungal Origin
from Different Ecological Niches
Although the discovery of endophytic fungi dates as far back as the early 1900s,
they did not receive much attention until the recent realization of their pharma-
ceutical and ecological significance (Gunatilaka 2006 ). Recent developments of
screening technologies have revealed that endophytic fungi are an outstanding
source of biologically active compounds with promising medicinal and agricultural
applications (Aly et al. 2011 ).
Tropical rainforest ecosystems are the richest ecosystems in the world containing
more than half of the Earth’s biota (Wilson 1988 ). The extreme biological diversity
of tropical rainforests ultimately implies the chemical diversity resulting from the
constant chemical innovations that exist in such ecosystems (Strobel and Daisy
2003 ). In tropical rainforests, the resources are limited due to the high species
diversity, therefore competition among species is high, and the selection pressure is
at its peak (Strobel and Daisy 2003 ). These factors eventually make rainforests a
potentially productive source for the discovery of novel molecular structures and
biologically active metabolites (Redell et al. 2000 ; Strobel and Daisy 2003 ).
Specific endophytes may have evolved within endemic plant species in areas of
high plant endemicity with moist, warm, and geographically isolated climates
(Strobel 2003 ; Strobel and Daisy 2003 ). This has been reported in rainforests of
Venezuela, Central America, monsoonal areas of Australia, golden triangle of
Thailand, Papua New Guinea, Madagascar, and upper Amazon regions
(Mittermeier et al. 1999 ). Novel endophytic fungal taxa and series of new bioactive
compounds have been discovered from each of the above areas (Mittermeier et al.
1999 ).
On the other hand, Strobel ( 2003 ) has stated plants growing in extremely moist
conditions or plants growing in rainforests which have a more or less constant 90–
100% relative humidity are prone to attack by certain extremely pathogenic fungi,
thus specialized defensive mechanisms in such plants are necessary for their sur-
vival. Accordingly, such disease defences may have offered by endophytes asso-
ciated with the plant (Strobel 2003 ). A comparative study using statistical data,
revealed that tropical plant endophytes provide more active natural products and a
larger number of secondary metabolites in comparison to that of temperate plant
endophytes (Bill et al. 2002 ).
The metabolite demethylasterriquinone B-1, L-783,281(1), isolated from an
endophyticPseudomassarisp. collected from an African rainforest tree has acted as
an antidiabetic agent (Strobel et al. 2004 ; Zhang et al. 1999 ). Unlike insulin, this
non-peptide secondary metabolite (L-783,281) does not get ineffective in the
digestive tract and thus can be a lead for an orally ingested drug for diabetes.
Similarly, Ambuic acid(2)is an antifungal agent isolated from a common rainforest
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