Study On The Cultivation Of Sulfur-Oxidizing Functional Bacteria And Remediation Of Cadmium Contaminated Soil

Soil is the basis for the survival of humans and other organisms.With the continuous development of industrialization and urbanization,a large amount of cadmium（Cd）enters the soil.Cd-contaminated soil is an urgent ecological problem to be solved.There is an urgent need to find a green,economic,and efficient remediation method to reduce the damage caused by Cd-contaminated soil.Traditional physical,chemical,and phytoremediation techniques have the disadvantages of large amount of engineering,high cost,and easy to produce secondary pollution.However,with the development of biological science,microbial technology has been widely used in soil remediation in recent years.In this study,sulfur-oxidizing functional bacteria were used to treat Cd-contaminated soil by microbial leaching.Firstly,the native sulfur-oxidizing functional bacteria were enriched from Cd-contaminated soil,and then continuously passaged and adaptively cultured.The changes in physicochemical properties of the sulfur-oxidizing functional bacteria and the removal efficiency of Cd from the soil were studied by gradually expanding the culture.Then,the Cd-contaminated soil was repaired under the condition of short time stirring and high solid-liquid ratio system.The basic physical and chemical indexes of the repaired soil,the contents of total Cd and available Cd（DTPA-Cd）,the removal efficiency of Cd and the percentage of Cd fraction were measured and analyzed.Using microbial high-throughput sequencing,we analyzed microbial diversity,bacterial community structure,and species richness in the restored soil.The correlation between microorganisms and soil changes was elucidated by correlation analysis.Key findings were as follows:（1）There is a significant negative correlation between the p H of the sulfur oxidation functional bacterial solution and the contents of ORP,EC and T-Fe,while the T-Cd content has a significant positive correlation with the contents of T-Mn and T-Fe.There was no significant difference in the removal efficiency of Cd from the contaminated soil between the continuous acclimated culture and the staged culture under the 1%treatment,but there were significant differences with the increase of time in the 10%,40%and 70%treatments.In addition,the removal efficiency of acclimation culture treatment is always higher than that of subsection culture treatment.The higher the solid-liquid ratio,the more obvious this situation is.（2）The addition of sulfur-oxidizing functional bacteria significantly reduced the contents of total Cd and DTPA-Cd in soil,with the removal efficiency of 39.6%and 64.5%,respectively.The removal efficiency of Cd increased with the decreases of soil p H.Sulfur-oxidizing functional bacteria increased the contents and availability of nutrients(available N,available P,total N,total K,exchangable Ca^2-,and available Mn)in soil,which reduced the uptake of Cd by rice tissues and effectively promoted rice growth.（3）Firmicutes（55.4%）and Proteobacteria（43.9%）were the dominant microbial phyla in the sulfur-oxidizing functional bacteria.Soil remediation with sulfur-oxidizing functional bacteria increased the relative abundance of Acidobacteria,while decreased the relative abundance of Proteobacteria.Sulfur-oxidizing functional bacteria did not change the composition of soil microbial community,but only changed the proportion of local bacterial species.（4）Soil microbial community was positively correlated with soil p H,but negatively correlated with soil ORP,available P and available Mn.Sulfur-oxidizing functional bacteria can increase the removal amount of Cd fraction soil by regulating soil p H and relative abundance of microorganisms,reducing the availability and availability of Cd in soil,thereby reducing the uptake of Cd by rice tissues,and improving soil nutrient levels,thereby increasing rice yield.