Study On The Remediation Of Cadmium-contaminated Rice Soils By Serratia Sp.X10

Because of human industrial activities,excessive mining,and extensive use of phosphorus-containing fertilizers and pesticides,a large amount of cadmium has flowed into the environment.Chinese Cd-production ranks first in the world,and the area of cadmium pollution has reached 220,000 km²,so the situation of cadmium pollution has become increasingly severe.Microbial remediation is different from traditional remediation methods with the characteristics of emerging green and efficient,and has been studied.In this study,the strain X10 with high cadmium resistance was isolated from a cadmium-contaminated soil in Shaoguan,Guangdong Province.The MIC of this strain for Cd²⁺reached 5 m M,and it could remove 0.2 m M Cd²⁺in LB medium for 96 hours.The strain X10 is a facultative anaerobic bacteria that can produce H₂S,urease and biofilm.It can not only remove Cd²⁺in the medium,but also increase the p H of the medium to 8.8.Microscopy and Fourier Transform Infrared Spectroscopy（FTIR）found that the surface of the bacterial membrane of the strain can adsorb a certain amount of Cd²⁺,and after adding Cd²⁺,it can stimulate the strain to produce more biofilm;after the strain X10 adsorbs Cd²⁺,black particles appear in the periplasmic space of bacteria,indicating that Cd²⁺can accumulate in the periplasmic space of bacteria in a certain amount;before and after removing Cd²⁺,the change of the infrared absorption peak of the group shows that-OH,-NH₂ and-CN involve the Cd adsorption process,which also reflects the role of proteins and other substances in the bacterial membrane in the process of removing Cd²⁺.In the paddy pot experiment,the cadmium content in each part of the rice with the bacteria-added treatment was significantly（P<0.05）lower than the non-bacteria treatment.The Cd content in the brown rice was 0.16 mg/kg,which decreased by 78.7%.The cadmium content in roots,shoots and husks decreased significantly（P<0.05）by78.6%,57.1%,and 68.3%,respectively.The MDA content and CAT enzyme activity of rice in the bacteria-added treatment group during the rice filling stage decreased significantly（P<0.05）,indicating that the rice in the bacteria-added treatment was in a smaller stress environment and suffered less cadmium toxicity.Regarding the soil cadmium content,compared with the treatment with non-bacteria,the fraction that is easily used by plants in the added bacteria treatment group decreased by 32%,and the fraction that was difficult to be used by plants in the bacteria treatment increased by262%.The analysis of soil diversity in the rhizosphere of potted rice showed that the addition of strain X10 did not affect the original soil microbial community.In the paddy field,the cadmium content in roots,shoots,husks and brown rice dropped significantly（P<0.05）by 22%,62.8%,66.5%and 44.9%.Compared with the blank treatment plot without bacteria addition,the available fraction of cadmium in the soil with the X10 treatment decreased by 39%,and the difficult-to-use fraction of cadmium increased by 256%.In a word,Serratia sp.X10 in this study has a good cadmium removal ability and can significantly reduce the cadmium content in various parts of rice.Furthermore,strain X10 significantly reduced available Cd content and increased unavailable Cd content and in the rhizosphere soil compared to un-inoculated control.