Microbial Degradation of Estrogens in Engineered and Natural Polluted Environments in Bahrain

Abstract

Abstract: Microbial biodegradation is the main route for estrogen elimination from wastewater treatment plants (WWTPs) and polluted environments to avoid estrogens environmental hazard due to their endocrine-disruption and carcinogenic properties. However, information on the biodegradation of estriol (E3) and the synthetic estrogen ethinylestradiol (EE2) and involved microorganisms and their ecological relevance is very limited. In this study, raw sewage (inflow wastewater), activated sludge, and thickened sludge samples were collected from a municipal WWTP in Bahrain to isolate and characterize E3- and EE2-degrading microbial cultures. Three E3-degrading microbial consortia were obtained via enrichment culturing. The three consortia utilized E3 as a carbon source in minimal medium. On the contrary, pure bacterial cultures isolated from the consortia could not grow on E3 as the sole carbon source. Instead, they transformed E3 to 16a-OH-El as a key product. Phylogenetic analysis revealed that the E3-transforming bacteria were affiliated with the genera Hydrogenophaga, Microbacterium, and Gordonia. The inflow consortium (enriched from raw sewage) grew on and utilized E1, E2, in addition to E3 individually and as a mixture in minimal medium, raw sewage, and activated sludge microcosms; albeit EE2 was not degraded. Degradation of E3 by the inflow consortium proceeds via the 4,5-seco pathway, in which E3 is initially transformed to El. During E3 biodegradation in a 14-day experiment, the community structure of the inflow consortium underwent remarkable temporal changes. Up to day 6 of the biodegradation experiment, the inflow consortium was dominated mainly by the genera Achromobacter, Hyphomicrobium, Microbacterium, Cupriavidus, and Aminobacter. This community strongly shifted towards Croceicoccus estronivorus which dominated the community starting from day 8 till day 14. Growth of the inflow consortium on dimethylsulfoxide in the absence of estrogens eliminated E3-degrading members of the community, and the inflow consortium lost the E3 biodegradation phenotype. We conclude that natural estrogen-degrading microbial communities exist not only in activated sludge, but also in raw sewage. Complete mineralization of E3 requires concerted action of the several community members of the inflow 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. Time and substrate/products concentrations are important determinants of the community composition. Keywords: Estrogens, Estriol, Biodegradation, Activated sludge, 4,5-seco pathway, consortia.