A native bacterial consortium degrades estriol in domestic sewage and activated sludge via the 4,5- seco pathway and requires estriol to retain its biodegradation phenotype

Estriol (E3) is one of the natural steroid estrogens commonly detected in wastewater. Although microbial biodegradation is a key process for removal of steroid estrogens during wastewater treatment, estriol biodegradation, and biotransformation mechanisms, as well as the involved bacterial consortia remain to be revealed. We enriched three E3-degrading bacterial consortia from raw sewage (inflow wastewater) and sludge samples. These consortia were able to utilize E3; however, individual strains isolated from the consortia could not grow on E3 as the sole carbon source. Instead, they transformed E3 to 16α-hydroxyestrone (16α-OH-E1) as a key product. The E3-transforming bacteria were affiliated with the genera Hydrogenophaga, Microbacterium, and Gordonia. The inflow (IF)-consortium utilized estrone (E1), estradiol (E2), in addition to E3 individually and as a mixture in minimal medium, raw sewage, and activated sludge microcosms, whereas the synthetic estrogen ethinylestradiol (EE2) was not degraded. Degradation of E3 was initiated by transformation to E1 via transient formation of 16α-OH-E1 and then proceeded via the 4,5-seco pathway. The community structure of the IF-consortium strongly shifted toward Croceicoccus estronivorus, which dominated the community after 10 days of incubation. The IF-consortium lost the E3 biodegradation phenotype upon growth on dimethylsulfoxide in the absence of estrogens. We conclude that complete degradation of E3 proceeds via the 4,5-seco pathway and requires concerted action of several community members of the IF-consortium at different time intervals and depending on the substrate and product concentrations. However, functional resilience of the consortium is a crucial factor that needs to be carefully addressed.