54 Khaled A. Selim, Mohamed M. S. Nagia and Dina E. El. Ghwas
bacteria, and live in the intercellular spaces of their hosts and this also true for
marine plants including algae or seagrasses and also for invertebrate animals
including soft corals and sponges. Almost all endophytes release bioactive
secondary metabolites which may be implicated in a host-endophyte
relationship (Selim et al., 2012). As a direct consequence of the natural role of
endophytic secondary metabolites, they may ultimately to have applicability in
medical field for improving the drug discovery (Selim et al., 2011 and 2012).
A worldwide scientific effort is to isolate endophytes and to study their natural
products is now under way (Strobel, 2003).
Overall, the rational responses for studying endophytes as promising
sources of new therapeutic agents is the fact that this field of the science is an
unexplored area of biochemical diversity. Additionally, the focus on
endophytes as a potential source for pharmaceutical industry is due to the
reality that the endophytes contribute to the host by providing protection to
them with a variety of secondary metabolites (volatiles, insecticidal,
antimicrobial, hormones-like compounds and .... etc.). Some of endophytic
metabolites may be of interest clinically since they possess antibacterial,
antifungal, antimalarial and other interesting biological activities (Verma et al.,
2009 and Selim et al., 2012). Finally, one of major concern to the
pharmaceutical companies is the toxicity of any potential probable drug to
human tissues. Apparently, plants as a pool of endophytic microbes are a
eukaryotic system in which the endophyte exists. The metabolites synthesized
by the endophytes may have less cell toxicity; otherwise, they could destroy
the target tissues of the host. Thus, the host itself has naturally served as a
selection system for microbes producing bioactive molecules with reduced
toxicity toward eukaryotes. Therefore, the endophytes consider being an
important source of novel natural compounds and a notable growing trend is
the characterization of endophytic secondary metabolites in drug discovery
(Strobel, 2003; Verma et al., 2009 and Selim et al., 2012).
9. PHARMACEUTICAL ACTIVATES OF ENDOPHYTES
Endophytic variability must be acquired during long term of interaction
with the host, by genetic crossing, or gene transfer, or simply with mutations
or by a set of unsubstantiated mechanisms yet such as genetic exchange with
its hosts. It appears that, endophytes represent microbial factories of bioactive
secondary metabolites. For this reason, extensive investigations have been
carried out for chemical screening of novel metabolites that may have