**6.3 Antibiotics discovery**

Since the discovery of first antibiotic there has been tremendous improvement in human health. However by traditional techniques we can tap only known antibiotics identified from known organisms. However, soil metagenomics presents a greater opportunity for discovery of vast number of antibiotics yet to be discovered. Researchers have isolated new antibiotics, one of such example is Turbomycin A and B from a metagenomic library of soil microbial DNA [83]. Some of them, isolated the genes encoding enzymes required for synthesis of other antibiotics e.g., Voget and co-workers found one amidase-positive clone while general screening of a soil metagenomic library for biocatalysts [84]. Amidases are used in the biosynthesis of β-lactam antibiotics [85]. Chang and Brady reported a gene cluster *bor* from soil that encodes indolotryptoline based compounds, a small and relatively rare family of natural products that exhibit potent activity against certain tumor cell lines [86]. Through activity-based screening of *E. coli* plasmid library from four agricultural soil samples 45 clones were isolated which were showing resistant to tetracycline, chloramphenicol, kanamycin, minocycline, gentamicin, amikacin, aminoglycosides, streptomycin and rifampicin [87].
