Study On The Characteristics And Mechanism Of Pichia Guilliermondii ZJH-1 Reduction Of Cr(?)

Chromium(Cr)is a toxic heavy metal widely distributed in the natural environment and exists in the form of oxides formed in different valence states.Due to the special physical,chemical and biological characteristics,the solubility of chromium in water is very high.The most stable forms are Cr(?)and Cr(?).Cr(?)is highly toxic to biological cells and is a carcinogen of biological organisms.substance.In contrast.Cr(?)is less toxic and mutagenic than Cr(?).In addition,Cr(?)is an essential micronutrient for the human body.Therefore,eliminating chromium pollution in the environment can focus on reducing highly toxic and soluble Cr(?)to lowly toxic and insoluble Cr(?).Relative to the shortcomings of physical-chemical high cost,high energy and secondary pollution,microbial method is considered to be a green,low-cost and effective way.Based on this treatment advantage,this study conducted a systematic study on the characteristics and mechanism of the reduction of Cr(?)by yeast,and reached the following important conclusions:In this study.Cr(?)was used as a screening agent,and one strain of yeast capable of reducing Cr(?)was isolated from the intestinal fluid of long-term feeding of polyethylene plastic Indian rice borer(Plodia interpunctella(Hiibener))larvae.The strain ZJH-1,identified by morphological characteristics and molecular biology,showed that the strain was Pichia guilliermondii;the minimum inhibitory concentration(MIC)of the strain to Cr(?)was 17 mmol in solid medium/L and liquid medium 33 mmol/L:under the condition containing,50 mg/L Cr(?),the MICs of other heavy metals are Cu(?)13 mmol/L,Pb(?)6 mmol/L,Ag(?)4 mmol/L,Mn(II)16 mmol/L,Ni(?)3 mmol/L,Co(?)3 mmol/L,Cd(?)0.9 mmol/L and Hg(?)0.2 mmol/L;the optimal pH and temperature for reducing Cr(?)by strain ZJH-1 are 9.0 and 400C respectively;when the inoculation amount is 8%,the reduction effect of Cr(?)is the best;when glucose is used as electron donor,Cr(?)can be completely reduced within 48 h;Cu(?)can effectively promote the efficiency of strains to reduce Cr(?).Based on the above research the relationship between ZJH-1 anti-oxidation system and different concentrations of Cr(?)was further studied based on the resistance of ZJH-1 to Cr(?).Studies have shown that ZJH-1 is accompanied by an increase in reactive oxygen species(ROS).the activity of antioxidant enzymes(SOD,POD.GR.and CAT)in a bell-shaped curve during the reduction of Cr(?)at different concentrations,and malondialdehyde The content of MDA)increases with the increase of Cr(?)concentration.Finally,the location of chromate reductase(CChR)was determined by permeabilized cells.cell-free extract(CFE)and reduction of Cr(?)by cell debris,and the mechanism of ZJH-1 reduction of Cr(?)was further explored.The results showed that:CChR is mainly located in CFE:by analyzing the infrared absorption spectrum(FTIR)of the bacterial cell and the full-wavelength ultraviolet scanning of CFE,the analysis shows that the carboxyl,amide,hydroxide and other groups of the cell wall and CFE pass through Cr(?)and Cr(?)Complexation and participate in the hioremediation of Cr(?);the SDS-PAGE electrophoresis of CFE shows that after treatment with different concentrations of Cr(?),strain ZJH-1 has molecular weights of 15 kDa,18 kDa,35 kDa,62 kDa The 115 kDa protein expression increased significantly,indicating that the reduction of Cr(?)by ZJH-1 depends on the yeast secretase;with Cr(?)as the reducing substrate,the optimal temperature range of CChR is 40? and the optimal pH is 7.0,Cu2+can enhance the activity of CChR:at the optimal temperature and pH.the KmR of this strain is 0.40 ?mol and the Vmax is 14.48?mol/L/min.