Effect And Mechanism On Siderophore-producing Bacterium Pseudomonas Umsongensis CR14 Reduces Soil Available Cd And Inhibiting The Absorption Of Cd In Wheat

Soil heavy metal pollution caused by human activities has a significant impact on food safety production,and the increase in Cd input in the biological chain may threaten related ecosystems and human health.Relevant researchers are committed to finding environmen-tally friendly soil heavy metal pollution remediation methods,and microbial functional strains that reduce the absorption of heavy metals by plants have been widely reported.However,the effect and mechanism of bacteria in reducing soil available heavy metals are poorly understood.In this study,we screened functional strains that efficiently reduce soil available Cd,and studied the Cd inactivation effect and mechanism of the strains.The research results can provide a theoretical basis and practical basis for the safe production of wheat as a remediation agent for Cd pollution in farmland.In this study,a strain Pseudomonas umsongensis CR14 was screened from the rhizosphere soil of wheat contaminated by Cd,which is resistant to heavy metals and can effectively inactivate Cd in the soil.The effect of strain CR14 on the adsorption and immobilization of heavy metals under solution conditions was explored,and the results showed that the removal rates of Cd in solutions containing 1.0 mg L^-1,5.0 mg L^-1,and 10.0mg L^-1Cd by strain CR14 were 61%,55%,34%,mainly through the adsorption and complexation of the bacterial cell wall Cd²⁺.The effect and mechanism of strain CR14inactivating effective Cd in sterilized soil and unsterilized soil were explored under soil conditions.The results showed that the inactivation effect of strain CR14 on effective Cd in sterilized soil and unsterilized soil was 18%,respectively.And 34%.Pseudomonas putide KT2440 of the same genus under soil conditions had 22%and 16%inactivation effects on effective Cd in sterilized soil and unsterilized soil,respectively.Comparing the biological characteristics of the two strains,it is inferred that CR14 affects the microbial community structure of unsterilized soil through high-yield siderophores,thereby efficiently reducing soil available Cd.A 150-day long-term soil fixation test was set up under soil conditions to study the inactivation effect and stability of the strain CR14 in the soil.The results showed that the strain CR14 was in sterilized soil for 30 days,60 days,90 days,120 days,and 150 days.The effects are 15%,13%,12%,11%,12%,respectively.The effects of strain CR14 in unsterilized soil for 30 days,60 days,90 days,120 days,and 150 days are 26%,29%,27%,25%,25%,the inactivation effect of strain CR14 in unsterilized soil is significantly higher than that of sterilized soil;the plate count results show that strain CR14 can colonize stably in soil,and it can be used in sterilized soil for 30 days,The number of colonization for 90days and 150 days were 1.3×10⁶CFU g^-1,1.1×10⁴CFU g^-1,1.1×10⁴CFU g^-1,respectively.In unsterilized soil for 30 days,60 days,90 days,The number of colonizations at 120 days and 150 days were 6.3×10⁵CFU g^-1,7.9×10⁴CFU g^-1,and 8.2×10⁴CFU g^-1,respectively.The above results show that the unsterilized soil state remained basically stable 60 days after the inoculation treatment,and further analysis was made to study the mechanism of the strain CR14 inactivating soil Cd.The results show that the inoculation strain CR14 can reduce the exchangeable Cd content of soil by 24%,the carbonate-bound Cd content by54%,the iron-manganese oxidation state Cd content by 21%,and the organically bound Cd content by 31%,thereby reducing the content.Soil available Cd content.Using metagenomic sequencing technology to analyze the 60-day unsterilized soil microbial community structure of each treatment group,the results showed that the bacterial community of the CR14 treatment group was significantly different from the non-inoculated CK group.First,the dominant flora changed.After CR14 treatment,the abundance of Proteobacteria was significantly reduced（CK:79.9%,CR14:28.4%）,and the abundance of Actinobacteria was significantly increased（CK:3.63%,CR14:34.9%）;the correlation analysis of environmental factors showed,Soil exchangeable Cd and carbonate-bound Cd content are positively correlated with Bacillus,Pseudoxanthomonas,etc.（r=0.67-0.92,p<0.05）,and negatively correlated with Gemmatimonadetes,etc.（r=0.74-0.88,p<0.01）;Soil iron and manganese oxidation state Cd content is positively correlated with Nocardioides,etc.（r=0.62-0.79,p<0.01）,and negatively correlated with Bordetella,Isometric（r=0.58-0.62,p<0.05）;CR14 inoculation treatment can reduce Brevundimonas,The abundance of Leclercia,Sphingomonas,Proteobacteria,etc.can increase the abundance of Actinobacteria,Chloroflexi,Frateuria,etc.,thus reducing the content of exchangeable and carbonate-bound Cd in the soil,and increasing the Cd content of iron and manganese oxidation state.The soil bacterial suspension of each treatment group was inoculated into sterilized soil,and it was found that the soil suspension of the CR14 group could reduce the soil available Cd content by 13%;about 100 bacteria were screened from the soil of each treatment group,and the CK group and the CR14 group were found The average values of the strains inactivating soil Cd were 7.7%and 11.4%,respectively,indicating that CR14 inoculation can change the structure of soil flora,and this change is conducive to the reduction of soil available Cd.The siderophore produced by the strain CR14 was extracted and identified and added to the soil exogenously,and the mechanism of CR14 affecting the soil flora was studied.The results showed that the siderophore produced by CR14 was iron pigment（Ferrichrome）and deferoxamine methanesulfonate（DFX-B）,when the concentration of DFX-B is 10 ng kg^-1,it can reduce the content of soil available Cd by 12.5%,which proves that strain CR14 affects the structure of soil flora by synthesizing and secreting DFX-B,thereby inactivating Cd in the soil.Under hydroponic conditions,the effect of strain CR14 on reducing wheat Cd absorption at a concentration of 1.0 mg L^-1Cd was studied.Compared with the uninoculated control,the inoculated strain CR14 can promote wheat growth（14%）and reduce wheat Cd absorption（5.6%）;laser confocal fluorescence microscope observation and plate colony count results show that the strain can colonize stably on the surface of wheat roots(10³CFU g^-1)and in the roots(10⁶CFU g^-1);simulate field conditions in wheat soil Cultivation test to study the practical application effect of strain CR14.Compared with the uninoculated control,strain CR14 can stably colonize the wheat rhizosphere(10⁶CFU g^-1)and root(10⁵CFU g^-1),and can be significantly Reduce the content of Cd in wheat roots（23%）and shoots（13%）,and reduce the available Cd content in wheat rhizosphere soil by 18.3%.