Bioactive Secondary Metabolites From Endophytic Fungi

New viral diseases, multidrug-resistant microorganisms, and infections by uncommon pathogens are emerging as new threats to human, plant, and animal health. Therefore, there is continuous need of discovery and development of new, safer, and effective drugs to combat these diseases. In the recent past, our drug discovery strategies heavily relied on microorganism where nearly 80% of the world's antibiotics have their origins. These microorganisms are mainly isolated from the soil and most of the world's soils have been screened out for the search of new microbes. Therefore, there is an urgent need to explore new microbial habitats for the microorganisms that produce novel bioactive compounds. “Endophytes” are the microorganisms which are present inside the living tissues of the plant by establishing a variety of relationships such as symbiotic, mutualistic, or parasitic with their host plants. In their relationship with the host plant, endophytes contribute to the plant by producing a plethora of substances that provide protection and survival benefits to the host plant. Endophytic fungi have been recognized as a novel source of bioactive secondary metabolites with diverse biological activities such as novel antibiotics, antimycotics, immunosuppressant, anticancer compounds, and so on to name a few. Their bioactive potential was first recognized when world's first multibillion dollar anticancer drug, paclitaxel (Taxol), was obtained from Taxomyces andreanae, an endophytic fungus isolated from the yew plant, Taxus brevifolia. However, it has been estimated that less than 1% of endophytic microorganisms are currently known, suggesting that a vast majority of them are yet to be discovered. Thus, endophytic microbes represent a potential source for the discovery of new and useful compounds, or new platforms for the organic synthesis of such compounds for the benefit of mankind. Moreover, plants located in the area of biodiversity hotspots of India, such as Eastern Himalaya, Western Ghats, and Andaman and Nicobar Island are believed to be host to novel endophytes with diverse chemical potential. The objective of the present article is to review the current state of information on the endophytes and their hosts, advances in isolation techniques, mode of cultivation, culture conditions, and biological activities of metabolites derived from endophytic microorganisms.