Biohydrogenation of Sterols by Eubacterium ATCC 21,408—Nova Species

Biohydrogenation of Δ5‐steroids was studied in vitro by incubating various steroids with a pure culture of Eubacterium 21,408 in a brain‐thioglycollate medium under anaerobic conditions. 1 Eubacterium 21,408, a strictly anaerobic bacterium, was isolated from rat cecal contents. It differed from any previously described Eubacterium species by its requirements for a Δ5‐3β‐hydroxy steroid. 2 Eubacterium 21,408 reduced the 5,6‐double bond of cholesterol, campesterol, β‐sitosterol and stigmasterol, exclusively yielding the corresponding 5β‐saturated derivatives. Similarly, the 4,5‐double bond of allocholesterol was reduced to yield coprostanol. Neither the 7,8‐double bond in 7‐dehydrocholesterol or in lathosterol, nor the 22,23‐double bond in the side chain of stigmasterol were reduced. 3 In the absence of a 3‐hydroxyl function (e.g. in cholest‐5‐ene), when the 3‐hydroxyl function was in the 3α‐position (e.g. in epicholesterol) or was substituted (e.g. in 3β‐chloro‐cholest‐5‐ene and in cholesteryl esters), no saturation of the 5,6‐double bond was observed. 4 When incubated with Eubacterium 21,408, the carbonyl group of 4‐cholesten‐3‐one, was reduced to the corresponding 3β‐hydroxyl group along with saturation of the 4,5‐double bond. The bacterium also reduced the 3‐oxo group of cholestanone and coprostanone to a 3β‐hydroxyl group.