This cluster of papers focuses on the microbial transformation and degradation of steroids, particularly cholesterol, by various microorganisms such as Mycobacterium tuberculosis and actinobacteria. It explores the enzymatic processes involved in steroid metabolism, including the role of cholesterol oxidase and 3-ketosteroid dehydrogenases. The cluster also delves into the biotechnological applications and potential biotransformation of steroids for drug development.