Tapping uncultured microorganisms through metagenomics for drug discovery

Natural products have been an important historical source of therapeutic agents. Microorganisms are major source of bioactive natural products, and several microbial products including antibiotics, anti-inflammatory, anti-tumour, immunosuppressants and others are currently used as therapeutic agents for human and  domestic animals. Most of these products were obtained from cultured environmental microorganisms. However, it is widely accepted that a very large majority of the microorganisms present in natural  environments are not readily cultured under laboratory conditions, and therefore are not accessible for drug  discovery. Metagenomics is a recent culture-independent approach that has been developed to access the  collective genomes of natural bacterial populations. It enables discovery of the diverse biosynthetic pathways encoded by diverse microbial assemblages that are known to be present in the environment but not-yet  cultured. Recently, several new bioactive molecules and proteins have been discovered using a metagenomic approach. This review highlights the recent methodologies, limitations, and applications of metagenomics for the discovery of new drugs. Moreover, it shows how a multidisciplinary approach combining metagenomics with other technologies can expedite and revolutionize drug discovery from diverse environmental microorganisms. Key words : Microbial diversity, metagenomics, natural products, drug discovery, microbial ecology.