Mycobacteria are able to degrade natural sterols and use them as a source of carbon and energy. Several genes which play an important role in cholesterol ring degradation have been described in Mycobacterium smegmatis. However, there are limited data describing the molecular mechanism of the aliphatic side chain degradation by Mycobacterium spp. In this paper, we analyzed the role of the echA19 and fadD19 genes in the degradation process of the side chain of cholesterol and β-sitosterol. We demonstrated that the M. smegmatis fadD19 and echA19 genes are not essential for viability. FadD19 is required in the initial step of the biodegradation of C-24 branched sterol side chains in Mycobacterium smegmatis mc²155, but not those carrying a straight chain like cholesterol. Additionally, we have shown that echA19 is not essential in the degradation of either substrate. This is the first report, to our knowledge, on the molecular characterization of the genes playing an essential role in C-24 branched side chain sterol degradation in M. smegmatis mc²155.
Keywords: M. smegmatis; cholesterol; microbial sterol degradation; sterol side-chain degradation; β-sitosterol.