Fe(III)-Aided Novosphingobium sp. ES2–1 Regulates Molecular\nMechanisms of 17β-Estradiol\nBiodegradation

17β-estradiol (E2) is one of the strongest environmental\nestrogens threatening wildlife and human health globally. Microbial\ndegradation is an alternative strategy to remediate E2-contaminated\nsites and may be regulated by ubiquitous Fe(III) in eco-environments.\nWe have previously obtained a high-efficiency E2 degrader, Novosphingobium sp. ES2–1, and investigated\nits metabolic pathway in connection with monooxygenase EstO1-induced\nring-B opening; however, the molecular mechanisms of ring-A cleavage\nin E2 are sorely lacking, especially under Fe(III)-aided regulation.\nHere, an extradiol dioxygenase EstN1 from strain ES2–1 involved\nin the ring-A cleavage of E2 was reported. It catalyzed the 4,5-<i>seco</i> reaction of 4-hydroxyestrone (4-OH-E1, a key E2-oxidized\nintermediate) with the support of the electron transport chain consisting\nof ferredoxin EstN2 and ferredoxin reductase EstN3, resulting in a\nring-A <i>meta-</i>cleaved product. Interestingly, Fe(III)-assisted\nstrain ES2–1 consolidated the opening of rings A and B in E2\nby reinforcing the expression of <i>estO1</i> and <i>estN1</i> genes, consequently enhancing E2 metabolism. Compared\nto Fe(III) starvation, the biodegradation half-life of E2 was sharply\nreduced from 1.35 to 0.59 d after Fe(III) supplementation. Simultaneously,\nthe transcription of <i>estO1</i> and <i>estN1</i> genes increased clearly from 4.3 to 47.5 times and 6.6 to 246.8\ntimes after Fe(III) induction, respectively, accompanied by remarkable\nimprovement in the abundance of ring-A/B cleavage products and their\npyridine derivatives. These findings highlight the significance of\nFe(III) in regulating the microbial remediation of environmental estrogens\nat the molecular level.