Suspensions of washed, resting‐stage cells ofClostridium bifermentanswere incubated with cholic acid under a variety of conditions in an attempt to manipulate the competing 7α‐dehydroxylation and 7α‐dehydrogenation reactions. Important variables thus identified were then tested in batch fermentation. Sodium thioglycollate was observed to inhibit dehydrogenation and to delay dehydroxylation. Zinc ion inhibited both dehydrogenation and dehydroxylation. In the presence of EDTA, near quantitative 7α‐dehydrogenation was achieved with no associated dehydroxylation. Finally, the presence of air in the fermenter headspace enhanced both transformations, possibly through an effect on the redox potential of
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