Modern biotechnology has a steadily increasingModern biotechnology has a steadily increasing demand for novel genes for application in various industrial demand for novel genes for application in various industrial processes and development of genetically modifi ed organprocesses and development of genetically modifi ed organisms. Identifi cation, isolation and cloning for novel genes isms. Identifi cation, isolation and cloning for novel genes at a reasonable pace is the main driving force behind the at a reasonable pace is the main driving force behind the development of unprecedented experimental approaches. development of unprecedented experimental approaches. Metagenomics is one such novel approach for engendering Metagenomics is one such novel approach for engendering novel genes. Metagenomics of complex microbial comnovel genes. Metagenomics of complex microbial communities (both cultivable and uncultivable) is a rich source munities (both cultivable and uncultivable) is a rich source of novel genes for biotechnological purposes. The conof novel genes for biotechnological purposes. The contributions made by metagenomics to the already existing tributions made by metagenomics to the already existing repository of prokaryotic genes is quite impressive but nevrepository of prokaryotic genes is quite impressive but nevertheless, this technique is still in its infancy. In the present ertheless, this technique is still in its infancy. In the present review we have drawn comparison between routine cloning review we have drawn comparison between routine cloning techniques and metagenomic approach for harvesting novel techniques and metagenomic approach for harvesting novel microbial genes and described various methods to reach microbial genes and described various methods to reach down to the specifi c genes in the metagenome. Accomplishdown to the specifi c genes in the metagenome. Accomplishments made thus far, limitations and future prospects of this ments made thus far, limitations and future prospects of this resourceful technique are discussed. resourceful technique are discussed.

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An esterase-producing clone Aph2 was isolated from the Apharwat soil metagenomic library, a mountain peak in NW Himalayas. ORF 2 (Est Ac) of clone Aph2 corresponds to 271 aa protein and showed 26 % sequence similarity to carboxylesterase gene of Synechococcus sp. JA-2-3B. Est Ac contains nucleophilic Ser in S68-X-X-K71 motif of β-lactamases with Tyr Y103. The conserved sequences are common with family VIII carboxylesterase and class C β-lactamase sequences. Phylogenetic analysis revealed that Est Ac sequence is closely related to esterase than to β-lactamases. In silico 3D protein structure of Est Ac was generated using MODELLER software (9.10 version). Model was generated on the basis of carboxylesterase template (PDB:1CI8) of Est B (Burkholderia gladioli) and the stereochemical parameters of the model generated were satisfactory. Docking with diisopropyl-fluorophosphate confirmed catalytic activity of Ser68 present in S-X-X-K motif.

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