ChoD and HsdD can be dispensable for cholesterol degradation in mycobacteria.

Cholesterol degradation is achieved through a complex metabolic pathway that starts with the oxidation of the 17-alkyl side chain and the steroid ring system. In bacteria, the oxidation of the 3β-hydroxyl group and isomerization of the resulting cholest-5-en-3-one to cholest-4-en-3-one is catalyzed by hydroxysteroid dehydrogenase (HsdD) or cholesterol oxidase (ChoD). Genes encoding both enzymes were annotated in both fast and slow growing mycobacteria, however the enzymatic activity was confirmed for HsdD, exclusively. Here, we used homologous recombination to engineer multiple mutants, and directly show that both ChoD and HsdD are dispensable for cholesterol degradation in fast-growing Mycobacterium smegmatis mc(2)155 and slow-growing Mycobacterium tuberculosis H37Rv strains. The mutants deffective in the synthesis of ChoD, HsdD or both enzymes were able to grow in minimal media supplemented with cholesterol as a sole source of carbon and energy. Multiple mutants, defective in synthesis of ChoD, HsdD and ketosteroid dehydrogenase (KstD), showed attenuated growth in minimal medium supplemented with cholesterol and accumulated cholesterol degradation intermediates: androstendion (AD) and 9-hydroxy androstendion (9OHAD).