Mechanism Of Nonylphenol Degradation By Transcriptomic Analysis And Effect Of Bacteria-algae Degradation

Environmental hormones(also known as environmental disrupting chemicals)can interfere with the normal hormone levels of organisms and have potential threats to human health.Nonylphenol(NP)and bisphenol A(BPA)are two common environmental hormones that have attracted wide attention in recent years because they can enrich in marine organisms and transmit in the food chain.This study investigated the effects of different concentrations of NP and BPA on Chlorella pyrenoidosa(C.pyrenoidosa)growth(cell density and chlorophyll a content),photosynthetic activity(Fv/Fm),superoxide dismutase(SOD)activity,peroxidase(POD)and malondialdehyde(MDA)content.The results showed that different concentrations of NP and BPA inhibited the growth and photosynthetic activity of C.pyrenoidosa,and the inhibitory effects were positively correlated with the concentration of pollutants.Photosynthetic activity of C.pyrenoidosa was significantly inhibited when the concentration of NP and BPA treatment was up to 8 mg/L.However,the photosynthetic activity could recover gradually with culture time,indicating that C.pyrenoidosa is a species with high NP and BPA tolerance.The variation in the activities of SOD and POD suggested that NP and BPA caused oxidative stress in C.pyrenoidosa,which was efficiently increased SOD and POD activities to resist oxidative stress.Furthermore,the elevated MDA content in algae under all treatments indicated that both NP and BPA caused oxidative damage to C.pyrenoidosa.By measuring the degradation percentage of NP by C.pyrenoidosa and infer the structure of degradation products of NP,the degradation ability and mechanism of NP by C.pyrenoidosa were discussed.Based on the differentially expressed genes of the transcriptome also provide a molecular evidences for C.pyrenoidosa to respond to NP stress and NP degradation mechanism.After culturing for 120 h,the NP degradation efficiency of C.pyrenoidosa was 88.7%,59.1%,49.2% and 47.6% in the 2 mg/L,4 mg/L,6mg/L,and 8 mg/L treatment groups,respectively.The structure of metabolites analysis showed that all NP degradation productions contain complete benzene rings and benzene cyclic alkyl groups substituents have hydroxyl or carboxyl,indicating that the biodegradation of NP originated from the long alkyl chain of NP.In addition,the differentially expressed genes of C.pyrenoidosa under NP exposure and the enrichment of these genes on GO and KEGG metabolic pathways were analyzed by transcriptome analysis.The results of GO molecular function enrichment analysis showed that C.pyrenoidosa significantly up-regulated the genes related to antioxidant enzymes and superoxide dismutase to resist NP stress,and the over-expression of oxyreductase-related genes may play a role in promoting NP degradation.The results of KEGG metabolic pathway enrichment analysis showed that the expression of genes related to basic metabolic pathways in C.pyrenoidosa such as fatty acid biosynthesis,starch and sucrose metabolism,amino sugar and nucleotide sugar metabolism were inhibited by NP,besides the expression of photosynthetic activity-related genes were inhibited.Transcriptome analysis provided a basis molecular evidence for the stress response of C.pyrenoidosa under NP exposure as well as the NP degradation mechanism.In addition,in order to explore more effective NP biodegradation materials,the Acinetobacter sp.Tust-DM21 and C.pyrenoidosa were used to construct a bacteria-algae system.The experiment of NP degradation by the bacteria-algae system showed that Tust-DM21 and C.pyrenoidosa could grow together and improve the degradation efficiency of NP.The degradation efficiency of this system was as high as 56.0% under the conditions of p H 8.0,temperature 28℃,NP concentration of 30 mg/L,and bacteria-algae ratio of 1:2.In summary,as a common green algae,C.pyrenoidosa has strong adaptability and tolerance to NP and BPA,and can effectively remove NP and degrade it.Transcriptome analysis provides a theoretical basis for studying the tolerance and degradation mechanism of NP in C.pyrenoidosa.The mixed degradation of Tust-DM21 and C.pyrenoidosa can effectively improve the efficiency of NP degradation.Therefore,the system can be used as a biodegradable material for NP and applied to the environmental treatment of sewage containing NP.