Physiological Responses And Molecular Mechanism Of Pycnoporus Sanguineus To The Stress Of Co-existed Tetrabromobisphenol A (TBBPA) And Hexavalent Chromium

Tetrabromobisphenol A?TBBPA?and Cr?VI?are two ubiquitous co-exsited pollutants in the e-waste dismantling regions.The environmentl problems caused by these concomitant pollutants have received increasing attention due to their high toxicity,strong persistence and mobility.Bioremediation is a promising method for the removal of toxic and harmful pollutants in the environment.In recent years,white rot fungi have been considered as a prospective alternative of the bioremediation in future due to its unique lignin degradation enzyme system and desired ability to eliminate heavy metals.Currently,the numerous researches about the bioremediation of contaminated environments using white rot fungi were primarily concerned with the remediation effect and mechanism,scarce study is underway to explore the physiological responses and molecular mechanism of white rot fungi under pollutants stress.Given this,in present study,Pycnoporus sanguineus,a typical species of white rot fungi,was chosen as a model strain.The objective of this work was to investigate the bioremoval of TBBPA and Cr?VI?combined pollutants by P.sanguineus and reveal the physiological response characteristic and the changes of proteomic profile of P.sanguineus in response to the stress of co-existed TBBPA and Cr?VI?.The detailed conclusions are as follows:?1?The removal efficiencies of TBBPA and Cr?VI?depended on the pH of reaction system,inoculum size and the initial concentration of pollutants.The removal efficiencies of Cr?VI?and TBBPA reached above 90%and 85%within 72 h and 48 h separately when the inoculum size was 4%?v/v?and pH was ranged from 3 to 5.With the increase of the initial concentration of Cr?VI?from 5 to 40 mg/L,the removal efficiency of Cr?VI?and TBBPA decreased from 92.5%and 75.4%to 30.6%and 44.8%,respectively.TBBPA of low concentration??10 mg/L?promoted the bioremoval of Cr?VI?and TBBPA,but exerted inhibition at high concentration?15-20 mg/L?.The extracellular enzymes of P.sanguineus played an important role in TBBPA degradation,the maximum degradation rate of 5 mg/L TBBPA by extracellular enzymes was 46.4%within 12 h.Cr?VI?could suppress the activities of MnP and Lac,thus posing an inhibition on TBBPA degradation.The maximum degradation rate of TBBPA by extracellular enzymes declined from 38.8%to 5.8%when Cr?VI?concentration increased from 5 to 40 mg/L,respectively.The addition of cytochrome P450inhibitor led to the decrease of TBBPA removal efficiency,suggesting cytochrome P450 also taken a part in the degradation of TBBPA by P.sanguineus.?2?High concentration of Cr?VI???20 mg/L?could obviously inhibit the fungal growth,organic acid secretion,cell viability and the activities of Na⁺/K⁺-ATPase,Ca²⁺/Mg²⁺-ATPase and T-ATPase and cause the cell membrane damage,fungal mycelia deformation and the release of cell inclusion.P.sanguineus had high resistance to TBBPA,TBBPA had nearly no influence on the fungal growth,cell viability,surface micromorphology and internal microstructure of the cell of P.sanguineus.Moreover,high level of TBBPA?15and 20 mg/L?obviously promoted the synthesis of intracellular proteins and improved the activities of Na⁺/K⁺-ATPase,Ca²⁺/Mg²⁺-ATPase and T-ATPase within the first 48 h of the reaction for enhancing the transportation and transformation of TBBPA.?3?The contents of ROS,H₂O₂,·OH and O₂^·-significantly increased after treatment with high level of Cr?VI???20 mg/L?.Cr?VI?-induced ROS resulted in the lipid peroxidation,as indicated by a noticeable increment of MDA content throughout the experiment.With the increment of Cr?VI?concentration,SOD and CAT activities along with GSH content increased within the first 24 h,but decreased afterward due to the impairment of the antioxidant system casued by Cr?VI?-induced ROS.Cr?VI?-induced oxidative stress further resulted in the mitochondrial depolarization,the enhancement of mitochondrial permeability,the release of cytochrome c and metacaspase activation,which ultimately led to the apoptosis of P.sanguineus cell.The DNA fragmentation and nuclear condensation and fragmentation were also observed in Cr?VI?-induced apoptotic cell.High concentration of Cr?VI???20mg/L?also brought about the disturbances of ion homeostasis in P.sanguineus,which was featured by K⁺effluxes and the overload of cytoplasmic and mitochondrial Ca²⁺.?4?Some ATP-binding cassette?ABC?transporters were obviously induced by these pollutants to accelerate the transportation,transformation and detoxification of TBBPA and Cr?VI?.Cr?VI?could inhibit the bioremoval of its organic co-pollutants TBBPA through suppressing the expression of several key proteins related to the metabolism of TBBPA by P.sanguineus,including two cytochrome P450s,pentachlorophenol 4-monooxygenase and glutathione S-transferases.Furthermore,Cr?VI?possibly reduced the cell vitality and growth of P.sanguineus by enhancing the expression of imidazole glycerol phosphate synthase as well as by decreasing the abundances of proteins associated with tricarboxylic acid cycle and purine metabolism.Cysteine synthase and cysteine desulfurase were found to down-regulate and up-regulate separately in Cr?VI?-containing treatments,thereby resulting in a reduction of glutathione biosynthesis after long-term exposure of Cr?VI?.Cr?VI?also inhibited the expression of peptidyl prolyl cis/trans isomerases,thus causing the damage of cell membrane integrity.Additionally,some important proteins participated in the resistance to Cr?VI?toxicity were observed to up-regulate,including heat shock proteins,26S proteasome,peroxiredoxins and three critical proteins implicated in S-adenosyl methionine synthesis,which contributed to reducing the hazard of Cr?VI?to P.sanguineus.In current study,we illuminated the mechanisms involved in the biotransformation of co-exsited TBBPA and Cr?VI?by P.sanguineus together with the physiological responses of P.sanguineus to the stress of these two concomitant pollutants at the cellular and proteic level.The results of this research will provide a theoretical and applied basis for the developing and popularizing white rot fungi-based bioremediation of the environments co-contaminated with brominated flame retardants and heavy metals,which is vital when attempting to better control the pollution in the e-waste dismantling regions through intensifing and regulating the microbial remediation.