Abstract
Steroid estrogens modulate physiology and development of vertebrates. Biosynthesis of C18 estrogens from C19 androgens by the O2-dependent aromatase is thought to be irreversible. Here, we report a denitrifying Denitratisoma sp. strain DHT3 capable of catabolizing estrogens or androgens anaerobically. Strain DHT3 genome contains a polycistronic gene cluster emtABCD differentially transcribed under estrogen-fed conditions. emtABCD encodes a cobalamin-dependent methyltransferase system conserved among estrogen-utilizing anaerobes; emtA-disrupted strain DHT3 can catabolize androgens but not estrogens. These data, along with the observed androgen production in estrogen-fed strain DHT3 cultures, indicate the occurrence of a cobalamin-mediated estrogen methylation to form androgens. Consistently, the estrogen conversion into androgens in strain DHT3 cell-extracts requires methylcobalamin and is inhibited by propyl-iodide, a specific inhibitor of cobalamin-dependent enzymes. The identification of the cobalamin-mediated estrogen methylation thus represents an unprecedented metabolic link between cobalamin and steroid metabolism and suggests that retroconversion of estrogens into androgens occurs in the biosphere.
Footnotes
The authors declare no conflict of interest.
