الفهرس 
Introduction and Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
Estrogens are removed in urine and faeces as unemployed polar conjugates, whether produced naturally by humans and animals or used in personal care products. In raw sewage and during sewage treatment, bacterial enzymes can modify conjugates into unconjugated estrogens (active forms).
The estrogens that allocate the treatment processes are then discharged into the environment via wastewater. As a result, treated wastewater is regarded as one of the most abundant sources of estrogen in the environment. Over the past few decades, researchers have done numerous studies in both labs and the field to learn more about what happens to estrogens in wastewater treatment facilities.
Although it has been proposed that estrogens are predominantly eliminated during sewage treatment by biodegradation, there is little information about the bacteria responsible for estrogen breakdown. Several human gut bacteria and oral microorganisms have been shown in preliminary experiments to be capable of using 17 β-estradiol as the sole carbon source.
The aim of this study was to isolate and screen different E2-degrading bacteria from wastewater using culture-dependent methods. Also, to determine the biochemical and molecular characterization and construction of the phylogenetic tree of the isolated bacterial genome. Further to identify uncultivated bacteria that may be present in the collected wastewater samples using culture-independent methods. Finally, to evaluate the degradation efficiency of the isolated strains under various environmental conditions.
This investigation involved the analysis of wastewater samples and the identification of bacterial communities. A culture-dependent technique revealed five different Gram-negative bacterial strains named (ASc1, ASc2, ASc3, ASc4, and ASc5) isolated from wastewater as E2-degrading bacteria. Based on analysis of the 16S rRNA gene sequence, the isolates belonged to Bordetella sputigena, Stenotrophomonas tumulicola, Pigmentiphaga daeguensis, Stenotrophomonas pavaini, and Serratia marcescens.
Using the culture-independent technique, 28 bacterial phyla, 53 classes, 104 orders, 226 families, and 559 genera were discovered. Bacteroidetes, Firmicutes, and Proteobacteria, accounting for (18 – 56%) of the classified sequences, were the most abundant phyla in all sequences. Other notable bacterial phyla were Actinobacteria, Cyanobacteria, Chloroflexi, Caldithrix, and Chlamydiae, which were detected in a low proportion (0.001 – 1.1%) of the classified sequences.
At the class level, the dominant classes among Bacteroidetes were Bacteroidia, Flavobacteria, and Sphingobacteria. Bacteroidia represent (49.7%) of all sequences. Regarding the Firmicutes phylum, three main classes were found within this phylum: Clostridia, Bacillus and Erysipelotrichi. Clostridia account for (50.1) percent of all sequences, which is considered the highest dominant class, while Bacillus sequences account for (5.1%) on average. Regarding the Proteobacteria phylum, the majority of bacterial sequences belong to the Gammaproteobacteria, Epsilonproteobacteria, Betaproteobacteria, Deltaproteobacteria, and Alphaproteobacteria classes.
Regarding the degradation efficiency of the isolated strains, the order of degradation percentages was Serratia marcescens, Stenotrophomonas tumulicola, Stenotrophomonas pavanii, Bordetella sputigena, and Pigmentiphaga daeguensis, which were (71.2%), (69.4%), (66.4%), (65.5%), and (59%) respectively. Within 48 hours of incubation, bacterial co-cultures comprising (ASc5 and ASc2), (ASc5 and ASc4), (ASc5 and ASc1), and (ASc5 and ASc3) could swiftly breakdown about (93.6%), (90.2%), (86.2%), and (82.9%) of E2 as the only carbon source in enrichment cultures, respectively.
In the enrichment cultures, the isolated strains (ASc1, ASc2, ASc3, ASc4, and ASc5) showed a clear ability to breakdown E2 at ideal conditions of 50 mg. L-1 of E2 as the initial substrate concentration, pH 7.00, a temperature of 30 ºC and a 5% inoculation volume of the reaction system.
Recommendations
Because E2-degrading strains have demonstrated their ability to reduce the potential environmental risks posed by E2, the removal and biodegradation of ecosystem pollutants should be investigated further.
More knowledge of the entire microbial community found in sewage water will aid researchers in improving the efficacy of the biodegradation of environmental contaminants.