The document discusses microbial biotransformation, which refers to biological processes in which microorganisms convert organic compounds into structurally modified reusable products through enzymatic reactions. It notes that biotransformation has several advantages over chemical synthesis, including specificity, mild reaction conditions, and reduced waste. Common biotransformation reactions include oxidation, reduction, hydrolysis, and isomerization. Examples of applications include producing steroids like testosterone and cortisone through microbial transformation, as well as transforming antibiotics, fatty acids, and degrading pollutants.