Antioxidative Reaction Of White Rot Fungi In Wastewater Under Heavy Metal Stress

With its low cost and will not cause secondary pollution, microbialtreatment is widely used in the treatment of heavy metal con taminatedwastewater. White rot fungi are proven to be effective in adsorbing heavy metalsfrom wastewater. Heavy metals can induce physiological stress to cells bygenerating large numbers of ROS, including H2O2, O2, OH and othersubstances, these substances can cause oxidative damage to biological cells.Antioxidant defense system determines the fate of the cells, thus it is essentialto maintain the balance of oxidation and reduction reactions in cells. Cellularantioxidant defense system consists of a series of non-enzymes and enzymes.They are involved in metabolism, proliferation, transcription, signaltransduction and many other activities. However, so far, the understanding ofthe mechanism of oxidative defense system is still not complete. Theref ore,investigation of the role played by oxidative stress enzymes in the process ofheavy metals adsorption is necessary for understanding the regulatorymechanisms of heavy metal toxicity in white rot fungi.Based on former studies, we chose Phanerochaete chrysosporium, which isone of white rot fungi as an object to investigate the change of heavy metalsadsorption rates and extracellular protein concentration under certainconcentration of heavy metal and pH; we also used classic methods to exploreLiP, MnP, POD, CAT activity changes over time.We found the pH of the medium decreased with time. Under th e incubationof low concentrations of cadmium (0~50μmol/L) and lead (0~25μmol/L), pHdecreased distinctly. The removal rate of cadmium was higher than lead byPhanerochaete chrysosporium. The heavy metals adsorption process could bedivided into two stages, the first lasts about6h. In this stage, he avy metaladsorption rate rose fast. The second stage may last for many days, adsorptionrate slowed down and got stabilized at the8t hhour.The activities of intracellular POD, CAT and extracellular LiP, MnP weremeasured with classic method. Results sho wed that under incubation of50μmol/L Cd2+or25μmol/L Pb2+, activities of the four enzymes decreased firstand then increased. The reason may be that the addition of heavy metal caused the production of a large number of ROS, which can’t be removed promptly,thereby inhibiting the activity of the enzyme; we set up a series of concentrationof Cd2+(0~150μmol/L) and Pb2+(0~150μmol/L) to induce P. chrysosporium.The results showed that low concentration of metal ions could induceintracellular CAT and POD activities; well high concentration of heavy metalions would cause the irreversible damage to cells, resulting in the decrease ofenzyme activities. CYP450contents under Cd2+(50~150μmol/L) or Pb2+(50~100μmol/L) were greatly improved, whereby we conclude that too muchROS may stimulate the production of an intermediate product, which couldpromote the generation of CYP450and reduce intracellular ROS l evel. Thisstudy contributed to a better understanding of white rot fungi on heavy metaldetoxification mechanism, and also laid a theoretical foundation for effectiveuse of white rot fungi in heavy metal wastewater treatment.