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Year : 2001  |  Volume : 19  |  Issue : 4  |  Page : 171

Microbial biodiversity: Shotgun libraries to metagenome

Centre for Cellular & Molecular Biology, Uppal Road, Tarnaka, Hyderabad- 500 007, India

Correspondence Address:
Centre for Cellular & Molecular Biology, Uppal Road, Tarnaka, Hyderabad- 500 007, India

How to cite this article:
Shivaji S. Microbial biodiversity: Shotgun libraries to metagenome. Indian J Med Microbiol 2001;19:171

How to cite this URL:
Shivaji S. Microbial biodiversity: Shotgun libraries to metagenome. Indian J Med Microbiol [serial online] 2001 [cited 2021 Mar 2];19:171. Available from:

Prokaryotes have been around for more than 3.5 billion years. They were first identified by Leeuwenhoek 300 years ago and eversince they have occupied a pride of place in the biosphere. Despite this fact, microbial diversity as known today (5,000 species) is only a miniscule fraction of the actual biodiversity. The reason for knowing so little about microbes is attributed to the fact that these are tiny, microscopic and exhibit very little morphological variation. Further, the inability to establish pure cultures has been one of the major constraints in enumerating the extent of biodiversity. Thus there is a need to develop methods which would enable us to identify more than 95% of microorganisms that are normally not cultivated.
It is now possible to identify non-culturable bacteria by constructing “Shotgun Libraries”. Such libraries are constructed from DNA isolated directly from an environmental sample and thus represent DNA of all the microorganisms present in the sample and therefore could contain an assortment of rRNA genes present in all the microflora of the given sample. Sequencing of these genes would enumerate the total biodiversity of the sample since it would include both the culturable and non-culturable bacteria. This approach has now led to the identification of microbial biodiversity of diverse habitats and has provided compelling evidence for the existence of hitherto unknown microorganisms. Shotgun library is however limited in that it enumerates the extent of biodiversity but is deficient in that it does not provide information on the novel or unique genes present in the microbes. However, this access to the gross or total genetic information is now possible through the “Metagenome” approach.
Metagenome represents the genomes of the total microbiota found in nature and involves cloning of total DNA isolated from an environment sample in a bacterial artificial chromosome (BAC) vector and expressing the genes in a suitable host. Thus the metagenome approach apart from providing phylogenetic data based on 16S rRNA gene sequence analysis and enumerating the extent of microbial diversity, also provides access to genetic information of uncultured microorganisms. In fact metagenome libraries could form the basis for identification of novel genes from uncultured microorganisms. Recognising the potential of this approach molecular biologists and chemists from University of Wisconsin and Cornell University in the USA have under taken a project to establish the metagenome of “Whole-earth” (soil) to catalog genes for useful natural products such as streptomycin, actinomycin D, immunosuppressants and anticancer agents. Thus, it may not be too long before this approach is also customized to hunt for genes of interest in metagenomes from various habitats. 

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