A Comparative Study on the Biodegradation of 17β-Estradiol by Candida utilis CU-2 and Lactobacillus casei LC-1

Abstract

The release and fate of estrogens have attracted more and more public attention. Biodegradation is an important method for estrogen removal from the environment. However, few comparative studies concentrated on the degradation of 17β-estradiol (E2) by fungi and bacteria. In this study, the removal efficiencies of E2 by fungi (Candida utilis CU-2) and bacteria (Lactobacillus casei LC-1) were investigated through influencing factors, kinetics, and biodegradation pathways. The results demonstrated that both C. utilis CU-2 and L. casei LC-1 have the same degradation efficiency, and they can effectively degrade E2 (10 μM) with nearly 97% degradation efficiency. However, the biodegradation efficiency of the two strains only reached 20% when E2 was used as a sole carbon source, while it increased to 97% with 1.2 g/L sucrose, glucose, or sodium acetate supply, indicating the occurrence of co-metabolism. In addition, the results indicated that 35°C and 0.6 g/L sucrose favored the degradation. However, the addition of excessive carbon sucrose (10 g/L) significantly inhibited the biodegradation of E2. Besides, the degradation of E2 with ~0–10 g/L sucrose as co-substrate followed the first-order kinetics well. Through intermediate products analysis, 12 degradation products were identified, and they were mainly produced via hydroxylation and methylation, among others, among which C14H22O4 (m/z:[M + H]+ = 255) was detected as the product with the smallest amount of carbon in this study. Based on the detected products and previous studies, five biodegradation pathways were proposed. To our knowledge, there are few reports about the comparisons of E2 removal between fungi and bacteria. Moreover, the results confirmed that the strain CU-2 and the strain LC-1 may have similar degradation characteristics and metabolic mechanisms in the degradation of E2. This study may provide a promising bio-treatment method with low energy consumption for E2 removal from aqueous environments and help in understanding their biodegradation mechanisms.

Characterization and Degradation Pathways of Microbacterium resistens MZT7, A Novel 17β-Estradiol-Degrading Bacterium

“…Zhang et al also reported that the addition of carbon sources seemed to inhibit the degradation of E2, and concluded that strain FJ1 preferred the use of additional carbon sources over E2 [ 11 ]. There is also evidence that the efficiency of degradation of pollutants by degrading bacteria is influenced by the concentration of added carbon sources [ 24 ]. In the future, the mechanism of E2 degradation by strain MZT7 needs to be further studied.…”

“…At a retention time of 13.07 min, the substance P1 was identified as estrone (E1). In almost all studies on microbial degradation of E2, E1 has been detected as an intermediate metabolite [ 14 , 17 , 19 , 20 , 24 , 42 ], and it is the main degradation product of E2 [ 2 , 4 ]. Moreover, many studies suggest that microbial degradation of E2 begins first with the D-ring, where the hydroxyl group at C-17 is oxidized to a ketone group and E2 is converted to E1 [ 25 , 29 ].…”

“…However, most current research focuses on biological characteristics of functional bacteria, while little is known about the regulatory mechanisms and degradation genes involved in the degradation process [ 21 , 22 , 23 ]. To date, several possible estrogen biodegradation pathways have been proposed [ 11 , 14 , 21 , 23 , 24 ]. For example, it has been proposed that the E2 was dehydrogenized at C17 of ring D to yield estrone (E1) [ 25 ].…”

Investigating the Metabolism of Estrogens in Ligilactobacillus salivarius Strains Isolated from Human Milk and Vaginal Microbiota

“…The carbon backbone of steroids consists of four fused rings (named A to D) carrying different side substitutions (alcohol, ketone groups and carbon chains of up to ten carbon atoms). The oxidation of the steroid core and the degradation of side chains according to the fatty acid oxidation pathway are key reactions for their microbial degradation [ 54 , 55 ]. Although all our L. salivarius strains harbor seven genes encoding enzymes participating in estrogen metabolism, their capacity to degrade E2 differed significantly, suggesting that they may exhibit different regulatory pathways, as previously reported [ 56 ].…”

“…Although substrate specificity is variable among them, these works suggest that, under substrate induction, different enzymes of this family can catalyze the conversion of E2 into E1, although in our case, to a lesser extent. Other degradation pathways of E2 that do not involve the initial conversion into E1 have been proposed for Lactobacillus casei LC-1, although the exact mechanisms have not been elucidated yet [ 55 ]. It should be highlighted that estrogen-degrading mechanisms have been widely studied in microorganisms isolated from soil, sewage and water, where the concentration of environmental estrogens may be relatively high [ 61 , 62 ].…”