16 alpha-dehydration of corticoids by bacteria isolated from rat fecal flora.

Two strains (No. 144 and No. 146) of rat intestinal anaerobic bacteria, phenotypically similar to Eubacterium lentum, were isolated and found capable of 16 alpha-dehydrating corticoids. The initial step in the 16 alpha-dehydration of 16 alpha-hydroxyprogesterone was dehydration at the C-16 and C-17 position with the accumulation of 16-dehydroprogesterone. This step required the side chain at C-17. In bacterial cultures the 16-dehydroprogesterone was then slowly reduced to iso-progesterone. 16 alpha-Hydroxypregnanolone was also converted to iso-pregnanolone by these bacteria. 16 alpha-Dehydratase was easily demonstrated in cell fractions of strain No. 144 incubated either aerobically or anaerobically. The same extracts did not convert 16-dehydroprogesterone to iso-progesterone under similar assay conditions. 16 alpha-Dehydration occurred at all substrate concentrations tested (20 to 200 micrograms/ml) provided the pH of the growth medium was between 6 abd 8 and the Eh below -130 mV. Strain No. 146 had both 16 alpha-dehydration and 21-dehydroxylation activities. The two enzymes functioned independently. A role for intestinal bacteria in the biotransformation of biliary 16 alpha-hydroxylated steroids and subsequent excretion in the urine is proposed.