Keywords Secondary metabolitesEndophytesTherapeutic applications
Bioprospecting
10.1 Introduction
Secondary metabolites are naturally derived substances from plants, animals, and
microorganisms (Baker et al. 2000 ). Plant secondary metabolites are known to pro-
vide protection from pathogen invasion to their host plant (Yang et al. 1994 ). As per
world health organization (WHO) estimates, 80% of the people in the developing
countries use traditional plant derived drugs for their primary health need. Moreover,
plant secondary metabolites have featured significantly in the treatment of many
diseases as well as used as base substances for the development of efficient drugs. For
example, Digitoxigenin, a steroid glycoside produced byDigitalis purpura,is the
oldest of the commonly used compounds in the treatment of heart diseases. After the
discovery of Penicillin, the wonder drug, followed by advancement in the fermen-
tation technology for cultivation of microbial cells, the potential of microbes as a good
source of secondary metabolites was recognized by world scientific community.
Microorganisms produce a range of secondary metabolites, many of them novel/new,
apparently as a part of survival/adaptation strategy to overcome constant metabolic
stress and challenging environmental conditions that they live and encounter con-
tinuously (Schutz 2001 ). On the other hand, despite the abundant biological diversity
of plants on earth, discovery of bioactive secondary metabolites has focused on
microorganisms which were mainly isolated from soil. Therefore, selection of the
ecological niche for isolation of the desired microbes is an important stage in new drug
discovery rather than using a totally random approach.
Throughout history, humans have used plants and plant-derived medicines to treat
all kinds of illnesses. However, extensive use of plant derived medicines has ques-
tioned the survival of many medicinally valuable and rare plant species. So it is a need
of hour tofind alternate sources and strategies for the production of bioactive
metabolites of plant origin. Approximately 0.4–0.5 million plant species exist on the
earth and, every plant inhabits/hosts one or other endophytic microorganism in its
internal tissues. Thus, this huge and relatively unexplored biodiversity can be tapped
for the search of novel microbiota significant for chemical and functional diversity.
De Bary ( 1866 )first coined and introduced the term“endophytes”. They are the
microbes that colonize inside the living internal tissues of the host plant without
causing any negative effect on them (Bacon and white 2000 ) and establish sym-
biotic relationship with their host. Among the endophytic microorganisms, the
endophytic fungi are highly diverse and are known to produce biologically active
and structurally diverse natural products of pharmaceutical importance. The
bioactive compounds isolated from endophytic fungi have been found to produce a
range of compounds/metabolites having diverse biological properties including
antimicrobial, antioxidant, antidiabetic, anticancer, antihypercholesterolemic, etc.
(Ruma et al. 2013 ). Use of endophytic fungi as a source of therapeutically important
214 S.I. Mohammed et al.