**3. Conclusion**

Due to microorganisms' abundant multienzyme systems, microbial transformation possesses advantages against chemosynthesis of environmental friendliness, mild reaction conditions, and high *stereo*-, *regio*, and *chemo*-selectivities as well as in improving conversion rates and reducing cost. Thus, microbial transformation technique is being increasingly used to structurally modify natural and synthetic compounds.

The hydrolytic and reductive capabilities of microorganisms have been known and are currently used in preparative and industrial reactions. Various classes of bioactive organic compounds have been subjected to enzymatic transformation to obtain more active and less toxic substances or to elucidate their metabolic pathways.

For example, biotransformation-derived steroids are used for a wide range of pharmacotherapeutic purposes, such as anti-inflammatory, immunosuppressive, progestational, diuretic, anabolic, as neurosteroids, and as contraceptive. Researchers continue to discover more useful steroid compounds and to isolate microorganisms that can perform the structural transformations desired. New technologies such as genomics, metanogenomics, gene shuffling, and DNA evolution provide valuable tools for improving or adapting enzyme properties to the desired requirements.

An alternative may be extremophilic microorganisms such as biocatalysts for countless future industrial applications that are more environmentally friendly.
