Screening Of Cadmium-Resistant Strains And Study On Cadmium Removal And Transformation Of Composite Bacteria Agent

In this study,the indigenous microorganisms on the contaminated site were screened and identified against heavy metal cadmium Cd²⁺strains,and the removal rate and morphological transformation of Cd²⁺were studied.At the same time,the effect of Morchella on the removal of heavy metal cadmium and morphological transformation was studied.Finally,the two were compounded into a composite inoculum.The fermentation conditions and synergy of the composite inoculum were studied,and the following results and progress were made.1.In this study,a Cd²⁺Bacillus subtilis JX-2019-3 was selected from a heavy metal contaminated site through preliminary screening and rescreening of soil samples.The morphological,physiological and biochemical characteristics of strain JX-2019-3 and the16Sr RNA gene sequence were systematically studied.The results showed that the Cd²⁺-resistant strain JX-2019-3 is a gram-positive bacteria with positive gelatin liquefaction and starch hydrolysis.The phylogenetic tree has the highest sequence homology with Bacillus subtilis,reaching 97.6%.It is identified as Bacillus subtilis JX-2019-3?Bacillus subtilis JX-2019-3?.2.In this study,the removal rate and morphological transformation of heavy metal Cd²⁺of Bacillus subtilis JX-2019-3 were explored through shake flask culture test and static soil culture test.The results show that:Bacillus subtilis JX-2019-3 strain has a good removal effect on Cd²⁺.When the temperature is 30?,the p H value is 6,and the inoculation amount is 5%,the removal effect is the best,and the removal rate reaches more than 60%;Bacillus subtilis JX-2019-3 promoted the conversion of Cd in contaminated soil from exchanged to other forms.Compared with the control,after 30 days of treatment,the exchanged Cd content was reduced by 15.22%.3.This study explored the efficiency of Morchella SN-6 to remove heavy metal Cd²⁺through shake flask culture test and static soil culture test.The results show that Morchella SN-6 strain has a good removal effect on Cd²⁺.The temperature is 26?,When the p H value is 7 and the inoculation amount is 6%,the removal effect is the best,and the removal rate is over 46%;Morchella SN-6 can promote the conversion of Cd in contaminated soil from exchange state to other forms.Compared with the control,exchange The state of Cd content is reduced by 19.29%.4.This study optimized and analyzed the culture conditions of the Bacillus subtilis JX-2019-3 and Morchella SN-6 composite strains through response surface design,and obtained the multiple regression model equation of biomass for key factors.Y=34.86-0.63A+0.054B+0.26C+0.16D+0.16AB+0.11AC+0.46AD+0.76BC-0.74BD+0.077CD-0.38A²-1.45B²-0.40C²-0.69D²The equation has a good degree of fit,in which A?carbon source?and D?bacterial ratio?,B?nitrogen source?and C?p H?and B?nitrogen source?and D?bacterial ratio?interact significantly.The fermentation conditions of Bacillus subtilis JX-2019-3 and Morchella SN-6composite strains are as follows:carbon source is soluble starch,nitrogen source is beef extract,p H is 6,and the ratio of bacteria is 1:2?JX-2019-3:SN-6?,at this time,the biomass is 17.61 g/L.The removal rate of Cd²⁺by the composite bacteria is about 80%,which is higher than that of the two bacteria alone.After the compound bacterial agent treatment,the exchanged Cd content decreased by 32.37%,and the organically bound Cd increased significantly.