Identification of the EdcR Estrogen-Dependent Repressor in Caenibius tardaugens NBRC 16725: Construction of a Cellular Estradiol Biosensor

In this work, Caenibius tardaugens NBRC 16725 (strain ARI-1) (formerly Novosphingobium tardaugens) was isolated due to its capacity to mineralize estrogenic endocrine disruptors. Its genome encodes the edc genes cluster responsible for the degradation of 17β-estradiol, consisting of two putative operons (OpA and OpB) encoding the enzymes of the upper degradation pathway. Inside the edc cluster, we identified the edcR gene encoding a TetR-like protein. Genetic studies carried out with C. tardaugens mutants demonstrated that EdcR represses the promoters that control the expression of the two operons. These genetic analyses have also shown that 17β-estradiol and estrone, the second intermediate of the degradation pathway, are the true effectors of EdcR. This regulatory system has been heterologously expressed in Escherichia coli, foreseeing its use to detect estrogens in environmental samples. Genome comparisons have identified a similar regulatory system in the edc cluster of Altererythrobacter estronivorus MHB5, suggesting that this regulatory arrangement has been horizontally transferred to other bacteria.