Until suitable methods for the isolation of specific micro-organisms for specific product were known, they were grown merely by providing optimum growth conditions for a given product, for example, nutrients, temperature, etc. In recent years, a revolutionary success has been made for the production of alcohols, vitamins, organic acids, ketones, enzymes, antibiotics, etc. on large scale by (i) characterization of strains, (ii) improvement of potential mutant and (iii) their further use for mass production of chemicals. It is the inherent ability of micro-organisms that they utilize a variety of organic substrates and result in a wide range of products through metabolic process. Owing to presence of biochemical diversity, micro-organisms have been commercially exploited by fermentation industry.