Isolation And Identification Of Phosphate Mineralization Bacteria And Its Adsorption And Mineralization On Cu

The high content of heavy metal in soil in China has far exceeded that of the international standard,which not only poses a threat to the safety of food production and the health of the ecosystem,but also affects human health through biomagnification of the food chain,making heavy metal pollution in soil a hot research topic at present.Microbial-induced mineralization in soil restoration is a green sustainable technology that can be applied in soil restoration while food are being produced and this technology has gradually gained people's attention in recent years.Therefore,this paper attempts to separate indigenous bacteria that can be mineralized by phosphate from the soil contaminated by heavy metal and conducts further study on its adsorption and biomineralization of Cu,providing excellent strain resources and technical support for the restoration based on microbial minerals for the soil contaminated by heavy metal.The main results are as follows:A strain LRP3 with potential for phosphate mineralization is isolated from the soil contaminated by heavy metal and this strain reaches logarithmic phase after growing for 24 hours in the medium containing sodium phytate.Meanwhile,the pH of the fermentation broth reaches 8.33,the activity of phytase and alkaline phosphatase are up to 50.06 and 1.8723 U·mL^-1 respectively.The strain LRP3 can produce extracellular secretion during the growth,which reaches 2.7 mg·L^-1 under the experimental conditions,and the tolerance concentration of strain LRP3 to Cu²⁺is120 mg·L^-1.Phylogenetic analysis and physiological and biochemical characteristics indicates that the strain LRP3 is Rahnella sp..The accession number of GenBank for the strain LRP3 is MH559341.1,and the collection number in China General Microbiological Culture Collection Center is CGMCC No.13347.The removal capacity of the fermentation broth of strain LRP3 on heavy metal ions is Cu²⁺>Zn²⁺>Pb²⁺>Cd²⁺,and the removal rate of aseptic fermentation broth,extracellular secretion?EPS?and bacterial cells on Cu²⁺also reaches more than 80%.When Cl^-is the accompanying anion,the removal rate of the fermentation broth and the sterile fermentation broth on Cu²⁺is higher than that of the accompanying anion being SO₄^2-.The adsorption of C?²⁺by strain LRP3 and its extracellular secretion can be divided into two stages:fast and slow stage.When the pH is 5.0,the concentration of C?²⁺is 50 mg·L^-1 and the adsorption time is 15 minutes,the adsorption rate of Cu²⁺by bacterial cells is the highest at 92.37%and the adsorption capacity is 23.093mg·g^-1.The adsorption kinetics accords with the quasi-second-order kinetic equation,and the isothermal adsorption model conforms to the Langmuir equation.The highest adsorption rate of Cu²⁺is 94.39%and the adsorption capacity is 23.598 mg·g^-1 when the optimal pH is 5.0,the concentration of Cu²⁺is 50 mg·L^-1,and adsorption time is10mins.The adsorption of Cu²⁺accords with the quasi-second-order kinetic equation,and the isothermal adsorption model conforms to the Freundlich equation.X-ray diffraction analysis,Fourier transform infrared spectroscopy and scanning electron microscopy as well as energy spectrum analysis show that the extracellular secretions are spherical after adsorption of Cu²⁺,the surface is filled with voids,and the particle size is about 10?m,but no mineral crystals are formed.After the adsorption of Cu²⁺,bacterial cells have good aggregation as well as irregular spherical surface and are closely packed.But while the fermentation broth of the strain LRP3 can form micro-spherical Cu3?OH?3PO4 mineral crystals with a particle size of about 10?m by phosphate mineralization,the aseptic fermentation broth can also produce mineral crystals by phosphate mineralization,but the mineral crystals are microspherical Cu5?PO4?2?OH?4 with a particle size of about 2?m.Infrared spectroscopy indicates that bacterial cell and the functional groups such as hydroxyl,carboxyl,amide,phosphate,amide I?protein peptide bond?and polysaccharide of EPS interacts with Cu²⁺,which results in the noticeable change in location of the characteristic peak and the absorption intensity.Increasing the amount of bacterial cells and EPS can enhance the cohesion and adhesion between cells and make the mineralized products more closely accumulated.Cl^-and SO₄^2-as accompanying anions have no obvious effect on the morphology of mineralized products.The available Cu in soil can be immobilized rapidly by strain LRP3 as well as EPS and the immobilization of strain LRP3 on available Cu in soil can be classified into three stages:adaptive stage-fast stage-slow stage.The content of available Cu in soil decreased by 58.2%after five days'culture in fermentation broth and this trend persisted after 30 days while that of the sterile fermentation broth decreased by53.4%over the same period,and tends to be stable after five days.Compared with bacterial cells and EPS,Cu²⁺immobilized by biomineralization in the fermentation broth of strain LRP3 has strong resistance to acidification and repeated freezing and thawing in a short time.In summary,the anti-copper Rahnella sp.LRP3 isolated from soil contaminated by heavy metal has strong alkali-producing and enzyme-producing ability,which can remove many kinds of heavy metals.Moreover,the fermentation broth and EPS also have strong adsorption and biomineralization on Cu²⁺and the phosphate minerals formed have good stability in soil.Therefore,the isolation and identification of strain LRP3 enriches the resource bank of phosphate mineralizing bacteria and has important application value in the rehabilitation of the soil contaminated by heavy metal.