Microbial degradation of the phytosterol side-chain to 24-oxo products

A mutant of the potent sterol degrader Mycobacterium fortuitum (ATCC 6842) has been isolated which is defective in its ability to degrade both the steroid nucleus and sterol side-chains that are branched at the 24-position. Bioconversions of phytosterol mixtures by this mutant resulted in the accumulation of the novel 24-oxo intermediates 9-hydroxy-27-nor-4-cholestene-3,24-dione (II) and 9-hydroxy-26,27-dinor-4-cholestene-3,24-dione (III). Under the same conditions, cholesterol is degraded mainly to 9-hydroxy-4-androstene-3,17-dione (I) by this organism.