Cadmium Resistance Mechanisms And Bioremediaion Potential Of A Bacteria Pseudomonas Sp.,AN-B15

With the rapid development of industry and agriculture,a large amount of heavy metal cadmium(Cd)has been discharged into the environment,resulting in a serious soil Cd pollution problem in China,which has seriously affected food security and endangered human health.Microbe-based remediation for heavy metal contaminated soils is a safe,economical,and simple technology.Plant growth-promoting bacteria can not only promote plant growth,but also prevent plants from absorbing heavy metals.Biochar can be used as a carrier of microorganisms,and also has a good remediation effect on heavy metal contaminated soil.Therefore,this study uses the plant growth-promoting bacteria Pseudomonas sp.,AN-B15 selected in our previous work to investigate its Cd resistance mechanisms and bioremediation potential.Moreover,the remediation mechanism by combination of biochar and strain AN-B15 was further investigated.Through wheat hydroponics,sand culture,and pot experiments,the effect of AN-B15 on the restoration of Cd pollution was studied.The research results provide theoretical basis and technical support for the safe use of Cd-contaminated farmland.(1)Functional bacteria AN-B15 has excellent Cd removal ability in liquid medium.MIC and EC50 of AN-B15 for Cd were 300.0 mg/L and 80.4 mg/L,respectively.In the liquid medium with the Cd concentration of 10-30 mg/L,the removal rate of Cd ranged from 59.10%to 93.56%.The initial pH has a significant effect on the growth of AN-B15 and the removal rate of Cd.When pH=5,the removal rate of Cd is the highest,reaching 74.28%.Desorption experiments showed that the removal of Cd by AN-B15 is mainly through biocomplex adsorption.Through TEM,XPS,XRD,FTIR analysis,bacteria AN-B15 mainly uses the functional groups hydroxyl,thio,carbonyl,and cyano groups on the extracellular polymer to complex and adsorb Cd,and also produce nano-Cd S particle precipitation.(2)The wheat hydroponic experiment found that compared with the Cd stress group,the AN-B15 strain inoculated significantly increased the root length,plant height,and plant weight of wheat by 50.33%,17.33%,and 26.42%,respectively,and significantly reduced the Cd content in the upper part of the wheat by 39.39%(p<0.05).The wheat sand culture experiment found that the inoculation of AN-B15 significantly increased the root length and root weight of wheat by 21.8%and 43.19%,and significantly reduced the Cd content in the ground and underground parts of wheat by 45.27%and 28.28%(p<0.05).In summary,it shows that AN-B15 can effectively reduce the toxicity and absorption of Cd to wheat.(3)The transcriptome analysis of AN-B15 showed that 1805 genes were differentially expressed,with up-regulated genes accounting for 22%and down-regulated genes accounting for 11%.Among them,the Czc ABC and Cad A genes related to Cd efflux and transport were significantly up-regulated,and the genes related to IAA and siderophore synthesis were also significantly up-regulated.they had no significant effect on the expression of ACC-deaminase and phosphorus-dissolving related genes.(4)Studies have shown that the combination of AN-B15 and biochar significantly improves the removal efficiency of Cd.When the Cd concentration is 50 mg/L and 100 mg/L,the Cd removal rate of biochar is 83.31%and 67.06%,respectively.When the bacteria AN-B15 is inoculated,the combined removal efficiency of biochar and AN-B15 increases to 96.67%and 91.32%.Analyses of XPS and XRD show that the bacteria AN-B15 can promote the precipitation of Cd CO₃,Cd(OH)₂,and Cd S to enhance the removal of Cd.Pot experiment results show that the combination of biochar and AN-B15 can promote wheat growth and reduce the Cd content of wheat roots.Compared with the CK+Cd control group,the root length and root weight of the bio+Cd and bio+Cd+AN-B15treatment groups increased by 20.35%,51.25%and 30.10%,90.00%,respectively,and the root Cd concentration decreased by 38.59%and 80.46%,respectively.Therefore,it is proved that the combined effect of biochar and AN-B15 has potential application value in the safe use of Cd-contaminated farmland soil.