Degradation Characteristics And Mechanism Of 17?-estradiol From Wastewater By Candida Utilis CU-2 And Lactobacillus Casei LC-1

Aquaculture wastewater discharge is an important way of estrogens exposure to the environment,which has attracted more and more attention of scholars around the world.Biodegradation is an important method to remove estrogens from the environment.However,there are few comparative studies on the removal efficiency of estrogens by different types of microorganisms,especially fungi and bacteria that widely exist in the water environment.In this study,17?-estradiol(E2)was used as a typical representative of estrogens.The removal efficiency,influencing factors,degradation kinetics,degradation pathway and degradation mechanism of E2 by fungi(Candida utilis CU-2)and bacteria(Lactobacillus casei LC-1)were systematically investigated.The results showed that E2 could be effectively degraded by Candida utilis CU-2and Lactobacillus casei LC-1 in the presence of sucrose,glucose or sodium acetate,and the degradation rate of E2 was close to 97%at the initial concentration of 10?M.However,when E2 was used as a single carbon source,the biodegradation efficiency of the two strains to E2 was only 20%,indicating that the degradation of E2 by the two strains was a co-metabolic process.In addition,it was found that 0.6 g/L sucrose and 35?were more conducive to the biodegradation of E2,while excessive sucrose could significantly inhibit the biodegradation of E2.The degradation of E2 by the two strains followed the first-order kinetics under the condition of 0?10 g/L sucrose.Through the analysis of intermediate products,twelve E2 degradation products were identified,and it was found that Candida utilis CU-2 and Lactobacillus casei LC-1had the same degradation products which were mainly produced by methylation and hydroxylation,among which C₁₄H₂₂O₄(m/z:[M+H]⁺=255)was the product with the lowest carbon content.According to the degradation products and previous studies,five biodegradation pathways of E2 were proposed.The micronucleus test of vicia faba root-tip showed that the toxicity of degradation solution to vicia faba root-tip became lower and lower with the decrease of E2 concentration during the degradation process,which indicated that the toxicity of E2 degradation products to the environment was less.According to the results of whole genome sequencing,eleven enzymes related to E2 degradation were identified,including dehydrogenase,oxidase and hydratase.These enzymes play an important role in the process of E2 degradation,such as redox and ring cracking.To our knowledge,there are few reports about the removal of E2 by Candida utilis CU-2 and Lactobacillus casei LC-1.The results show that Candida utilis CU-2 and Lactobacillus casei LC-1 are efficient estradiol-degrading microorganisms,providing a promising biological treatment method for the removal of E2 from aquaculture wastewater,and revealing the biological mechanism of E2 degradation.