Isolation And Identification Of Carbonate Mineralized Bacteria And Its Immobilization On Heavy Metals

With the development of agricultural production and the continuous advancement of industrialization and urbanization,all kinds of heavy metals will be a serious threat to soil environmental quality and production safety of agricultural products by means of atmospheric subsidence,fertilizer application,sewage discharge and surface runoff,etc.In the environment,there is a kind of carbonate minerals which can be formed by biological mineralization to form heavy metal microorganisms in soil,which has important application value in bioremediation of heavy metal contaminated environment.Therefore,in this paper,we try to isolate and obtain the bacteria which can carry out carbonate mineralization in the rhizosphere soil of farmyard,such as chicken manure and pig manure,and further study the mineralization mechanism,the mineralization of heavy metals in soil and the stability of the mineralized products,the main results are as follows:?1?The bacteria,phylogenetic analysis and physiological and biochemical characteristics of the bacterium,which can degrade urea to release carbonic acid and consolidated heavy metals by biological mineralization,were obtained,and the strain was named LAX2.The strain LAX2 can grow rapidly in the medium containing urea,the activity of urease is up to 140 U mL^-1,and the pH of fermentation broth can reach 9.06.The tolerance concentrations of strain LAX2 on Cu²⁺,Pb²⁺and Cd²⁺can be achieved by the 115 mg·L^-1?105 mg·L^-1 and 35 mg·L^-1,X-ray diffraction analysis?XRD?,Fourier infrared spectroscopy?FTIR?,Scanning electron microscope?SEM?and Energy spectrum?EDS?analysis showed that the strain LAX2 can form a large diameter micro-spherical crystal by biological mineralization,and can form Cu2?OH?2CO3,PbCO3 and CdCO3 minerals for single Cu,Pb and Cd respectively.The removal rate of Cu²⁺in solution was 93%,85%and 72%,the removal rate of Pb²⁺was 91.6%,86.3%and 67.4%,and the removal rate of Cd²⁺was92.2%,89.1%and 78.2%respectively,in the adsorption,biological mineralization and non mineralization of LAX2.?2?The study on the remediation heavy metal contaminated soil by strain LAX2 showed that the content of avaible Cu in soil was decreased by 52.3,73.7%and 87.4%respectively after culture 5,10 and 30 days,the content of Pb in soil decreased by 56.1%,76.5%and86.8%respectively.Compared with the adsorption of somatic cells and chemical precipitation,the immobilized Cu has a strong resistance to flooding and repeated freezing and thawing in the short term.After adding fermentation broth,aseptic fermentation liquid and germ cell to Pb contaminated soil,the potted experiment of pakchoi was carried out respectively,and compared with control,the plant height of pakchoi increased by 49.4%,21.6%and 9.6%respectively,and the content of Pb in soil decreased 78.1%,64.2%and52.4%respectively,The content of Pb in pakchoi decreased by 56.5%,27.4%and 14.5%respectively.Cd content in rice paddy soil was repaired by strain LAX2 fermentation broth,aseptic fermentation broth and germ cell,the Cd contents decreased by 35.3%,19.4%and12.5%respectively,the Cd content of stem and leaf decreased by 26.7%,15.6%and 8.4%respectively,and Cd content in rice grains decreased by 28.7.%,16.4%and 7.5%,the available Cd content of soil decreased by 56.9%,34.5%and 21%respectively.The above results showed that xylose-colorless bacilli isolated from plant rhizosphere soil have resistance and biological mineralization to a variety of heavy metals,and the mineralization products formed in soil have high stability.The heavy metal contaminated soil will not have adverse effect on plant growth,but can reduce the effective state content of heavy metal by biological mineralization,promote the growth of plants and reduce the absorption of heavy metals.Therefore,the strain LAX2 has important application value in the bioremediation of single and compound contaminated soil.