| Bisphenol A(BPA) is an endocrine disruptor that has attracted attention because of its toxicity and detection at relatively high levels in aquatic environments.Here,we isolated and identified a BPA-and nonylphenol-degrading algal strain as Desmodesmus sp.using morphological and molecular analyses.We investigated how BPA affects Desmodesmus growth(optical density,OD680)and photosynthetic activity(Fv/Fm),and also investigated BPA detoxification and biodegradation by algal culture.In cultures with an initial OD680 of 0.2,even the highest level of BPA exposure(33 mg L-1)failed to significantly inhibit Desmodesmus sp.Additionally,at the highest BPA exposure,a slight suppression was observed in the early stages at a lower density(OD680 0.04)and near-complete inhibition was observed for the lowest density(OD680 0.008)until the final 10 d,when growth and photosynthesis had recovered.For the OD680 0.2 culture,Desmodesmus sp.removed almost all BPA at all tested concentrations,whereas OD680 0.008 and 0.04 cultures respectively removed 75% and 82.3% BPA at the highest BPA concentration.BPA metabolites and biodegradation products were identified by using of LC-HRMS and in light of previous studies.We identified BPA,BPA oxidative hydroxylated products of monohydroxybisphenol A and 2-hydroxy-3-hydroxymethybisphenol A in peak C and their glycosides such as BPA glycoside,monohydroxybisphenol A glycoside and 2-hydroxy-3-hydroxymethybisphenol A glycoside in peak A.In addition,we identified monophenols as the oxidation products of BPA and hydroxylated BPA,such as 4-isopropanol-phenol,4-isopropenyl-phenol,4-isopropanol-benzene-1,2-diol,4-isopropenyl-benzene-1,2-diol and 3-hydroxymethyl-4-(1-hydroxy-1-methyl-ethyl)-benzene-1,2-diol.Moreover,we demonstrated that BPA glycosides can revert to BPA,suggesting that environmental BPA glycoside concentrations should be evaluated when examining the impact of BPA.Transcriptome analysis by using GO and KEGG pathway database showed that algae may significantly upregulated oxidoreductases,glycosyltransferase encoding genes for BPA oxidative biodegradation and adding glycosyl for detoxification.Significant enrichment of photosynthesis-antenna proteins,photosynthesis,carbon metabolism,citrate cycle,DNA replication pathways and over-expressed enzyme transcripts involved in may be responsible for the potential of BPA tolerance,detoxification and biodegradation in this green algae.Transcriptome analysis can gave some insight to the molecular response of Desmodesmus sp.toward BPA exposure.Also we investigated the joint-toxicity of BPA and NP to green algae Desmodesmus sp.and the effect on the biodegradation capacity by co-treated with two endocrine disruptors.Results showed that high tolerance to NP toxicity were found.The highest level of NP exposure significantly inhibit the growth and photosynthetic activity of Desmodesmus sp.,however,recovery was observed also.This indicated that Desmodesmus sp is well-tolerant and well-adapted to NP toxicity.Co-treated with BPA and NP showed a synergistic toxic effect on the growth and photosynthesis.Existence of NP in the medium promoted the biodegration of BPA by this algae when compared to that of exposed to BPA only.However,on the contrary,biodegradation rate of NP was found to decrease than treated with NP only.This result suggested that green algae may choose to metabolize the more polar toxicant for detoxification.Nevertheless,green algae Desmodesmus sp was demonstrated to have the high potential of BPA and NP removal.Lastly,we suggest that the Desmodesmus sp.is suitable for BPA and NP removal from contaminated aquatic environments... |
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