Molecular characterization of a new gene cluster for steroid degradation in Mycobacterium smegmatis

摘要: The C-19 steroids 4-androstene-3,17-dione (AD), 1,4-androstadiene-3,17-dione (ADD) or 9α-hydroxy-4-androstene-3,17-dione (9OH-AD), which have been postulated as intermediates of the cholesterol catabolic pathway in Mycobacterium smegmatis, cannot be used sole carbon and energy sources by this bacterium. Only ΔkstR mutant constitutively expresses genes repressed KstR regulator can metabolize AD ADD with severe difficulties but still 9OH-AD, suggesting that these compounds are not true side products pathway. However, we found some M. smegmatis spontaneous mutants mapped PadR-like (MSMEG_2868) efficiently all steroids. We demonstrated PadR allow expression a gene cluster named C-19+ (MSMEG_2851 to MSMEG_2901) encoding steroid degrading enzymes, expressed under standard culture conditions. has apparently evolved independently from upper kstR-regulon, both clusters converge on lower kstR2-regulon responsible for metabolism C D rings. Homologous only other actinobacteria steroids, remarkably it is absent tuberculosis.