Screening Of Cadmium Tolerant Strains And Their Absorption And Bioaccumulation Properties For Cd²⁺

In recent years,the impact of cadmium(Cd)pollution on aquatic ecosystems and human health has become increasingly serious,which had received great attention from the government and extensive attention of researchers.Among the existing water body Cd pollution treatment technologies,the microbial method is considered to be an effective and environmentally friendly low-cost method,but lacks high-tolerance strains and systems for in-depth adsorption and absorption characteristics studies.Therefore,the screening of cadmium-tolerant strains and their research on the absorption and bioaccumulation characteristics of Cd2+ have important theoretical and practical significance.Two cadmium-tolerant strains were selected from Cd-contaminated soil,and the characteristics of adsorption and bioaccumulation of Cd2+were systematically studied.The results can provide theoretical basis and technical support for the application of microbial remediation in water pollution control.The main conclusions are as follows:(1)Two strains of Cd-resistant Gram-negative bacteria X-A and X-D were selected from Cd-contaminated soil and preliminarily identified by 16SrDNA sequence analysis.The X-A strain is Burkholderia cepacia,GenBank accession number:MK418965;X-D strain is Ralstonia sp.,GenBank accession number:MK418966.(2)The tolerance threshold of X-A and X-D strains for Cd2+was 850 mg/L(plate culture)and 700 mg/L(liquid culture).The suitable growth conditions for X-A strain were:temperature 30?,rotation speed 120 r/min,pH 7.0;the suitable growth conditions of X-D strain were:temperature 25?,rotation speed 150 r/min,pH 5.0.(3)The optimum conditions for the adsorption of Cd2+by X-A strain are:dosage 0.1 mg/L,adsorption time 3 h,pH 7.0,temperature 40?;the optimal conditions for adsorption of Cd2+by X-D powder are:dosage 0.1 mg/L,adsorption time 2 h,pH 6.0,temperature 30?.The adsorption amount of Cd2+by X-A and X-D powders under optimal conditions was 166 mg/g and 198 mg/g,respectively.The adsorption process of Cd2+ by bacteria powder is more consistent with the Langmuir isotherm adsorption model and belongs to single layer adsorption.The adsorption of Cd2+ by bacteria powder is more in line with the second-order kinetic equation.Comparing the changes of SEM,EDS and F TIR before and after adsorption,it was found that the surface of the powder could adsorb Cd2+,and there was ion exchange between Cd2+and Na+and Mg2+.The adsorption of Cd2+ by the powder mainly through the hydroxyl,carbonyl and amide groups contained in the surface.A group such as a phosphate group is complexed with Cd2+.(4)The suitable conditions for strain X-A to bioaccumulation Cd2+in growth are as follows:initial concentration of Cd2+400 mg/L,culture temperature 30?,rotation speed 120 r/min,culture time 72 h,pH 5.0;The suitable conditions for X-D strain were:initial concentration of Cd2+ 400 mg/L,culture temperature 35?,rotation speed 120 r/min,culture time 96 h,pH 6.0.The suitable amount of Cd2+bioaccumulation by X-A strain(57 mg/g)was greater than that of X-D strain(46 mg/g).Subcellular component analysis showed that the Cd2+accumulation ratio of each component in the process of Cd2+uptake was as follows:the cell wall was the largest,the organelle was the second,and the soluble component was the smallest.The strain utilizes the ability of the cell wall to accumulate and transport the organelle to the cell wall to enhance its ability to adapt and absorb Cd2+.