Bioaccumulation Of Cadmium And Mechanism Of Burkholderia Cepacia GYP1 To The Cadmium Stress

Heavy metal pollution is an unavoidable environmental problem during the development of industrialization.Cadmium is one of the most toxic heavy metals,which posing a great threat to the ecosystem safety and human health.Bacterial remediation of heavy metal pollution has attracted the attention of many scholars because of its economic and security.In this study,we explored the Cd-tolerance and cadmium bioaccumulation ability under the oligotrophic environment of Burkholderia cepacia GYP1,which was isolated from contaminated farmland soil,and its micro-mechanism and molecular mechanism under cadmium stress.The study found that B.cepacia GYP1 has strong cadmium tolerance,which could grow in LB liquid medium containing 1000 mg/L Cd²⁺.It is resistant to a variety of heavy metals and the tolerance order was Cu>Pb>Ni?Zn>Cr>Cd>Co.In addition,GYP1 possessed highly accumulation capacity for cadmium reaching 116 mg Cd/g biomass?dry weight?.It had the bioaccumulation of 84.45 mg Cd/g dry biomass in 100 mg/L Cd²⁺medium at pH=6,and pH?3-6?just slightly affected the cadmium accumulation capacity of GYP1.GYP1 shows strong environmental adaptability.The mechanism of GYP1 Cd???accumulation under oligotrophic condition was investigated by different characterization methods.Zeta potential analysis of the bacterial surface showed that electrostatic adsorption played a role in the cadmium accumulation,especially in the initial phase of rapid adsorption.The results of ATR-FTIR analysis indicated that the functional groups such as carboxyl,amino,and phosphoryl groups on the outer membrane or EPS were involved in the removal of cadmium by complexation with them.The majority of cells could still maintain a complete structure even if interacting with 100 mg/L Cd²⁺for 7 days without nutrient supplement,which was verified by the results of the flow cytometry?FCM?.In addition,SEM-EDS and TEM-mapping observed the extracellular polymeric substance?EPS?on the cell surface,and cadmium signal was detected on both cell surface and intracellular.Cadmium distribution in subcellular fraction demonstrated that the uptake and distribution of cadmium varied with the increased amount of cadmium of GYP1 cell during the 7-day treatment time:the accumulation of cadmium was mainly on the outer membrane at the beginning?within 1day?,and the intracellular cadmium kept increased and held stable after 2 days,after that,the increased amount of cadmium mainly located extracellularly,related to the secreted EPS.While at low Cd²⁺concentration??20 mg/L?,cadmium removal was mainly depended on the intracellular bioaccumulation.The expression of GYP1 protein with and without cadmium stress was analyzed by iTRAQ-based quantitative proteomic.Compared with the control group?water?,there were 561differentially expressed proteins in GYP1 cells under 7-days cadmium stress,of which 284proteins were up-regulated and 277 proteins were down-regulated.Cells promoted the expression of Cd²⁺/Zn²⁺-exporting ATPase and type ? protein secretion system?T6SS?under cadmium stress to facilitate the Cd²⁺efflux and fix extracellular cadmium by secreting EPS.And GYP1 promoted the expression of glutathione S-transferase to enhance the complexation of Cd²⁺with glutathione,which could alleviate intracellular cadmium toxicity.The antioxidant system and DNA repair system were up-regulated,and the oxidative phosphorylation process was down-regulated to reduce the oxidative stress which was caused by cadmium.In addition,in order to provide the material basis and energy basis for cells under cadmium stress,cells accelerate the physiological processes of glycolysis,TCA cycle,pentose phosphate pathway,purine and pyrimidine metabolism,amino acid metabolism,which further increases its tolerance to cadmium.