Endophytic fungi: A potential source of bioactive compounds

Endophytic fungi are ubiquitous in nature and reside intercellular or intracellular in the plants, at least for a portion of their lives without causing apparent symptoms of infection. Almost all plants are known to harbor endophytes. The choice of the plant to be used for exploring endophytes for bioactive compounds is important. Secondary metabolites serve in multiple physiologic functions, many of which are common to both plants and microorganisms, and in a way it is intuitive that the same or similar compounds can be produced by ecologically associated entities. Thus, the aim to exploit botanical diversity for the discovery of novel drugs has led to the finding of microbial strains able to synthesize bioactive compounds which previously considered as typical plant products. In the last 25 years, the general evidence that all plants are inhabited by endophytic microorganisms, but in newer finding it was revealed that the latter are also capable of producing plant metabolites, which are considered as a major factor influencing the establishment and evolution of mutualistic interrelations. Therefore, medicinal plants which are known to be used since centuries as an alternative source of medicine are valuable source for bioprospecting endophytes. The fossil record indicates that plants have been associated with endophytic [1] and mycorrhizal [2] fungi for > 400 million year and was likely associated when plants colonized land, thus playing a long and important role in driving the evolution of life on land. For treating infectious diseases, bioactive natural products and their derivatives have historically served as a major source of therapeutic agents [3]. Endophytes have proven to be a rich source of novel natural compounds with structural diversity possessing a wide-spectrum of biological activities. However, fungi isolation in pure cultures has been limited. Less than 5% fungal isolates have been successfully isolated into pure cultures out of over one million fungal endophytes existed in the nature [4]. Endophytic fungi isolated from medicinal plants are more likely exhibit pharmaceutical potentials.