Microbial transformation of sterols to C19-steroids by Rhodococcus equi.

A wild-type strain of Rhodococcus equi, isolated from soil, degraded cholesterol, β-sitosterol, stigmasterol and mixed sterois to androst-4-ene-3,17-dione (AD) and androsta-1,4-diene-3,17-dione (ADD). A definite preference for a relatively simply structured cholesterol side chain was observed. Highest specific cholesterol side-chain cleavage was associated with active growth of the culture. Maximum yield of ADD was obtained when sodium acetate and cholesterol were incorporated together in the medium. Specific side-chain cleavage required the presence of 2,2'-dipyridyl, an inhibitor of ring cleavage.