Screening Of Cadmium-resistant And Phosphorus-dissolving Bacteria And Their Cooperative Phytoremediation Of Cadmium-contaminated Soil In Coal Mines Area

With the continuous increase of mining,mineral processing and smelting activities,heavy metal pollution in the mining area and surrounding soil has become more and more serious,and the research and development of contaminated soil remediation technology has become one of the research hotspots in the environmental field.Traditional physical and chemical repairs have many defects,not only the large amount of engineering,high cost,but also the use of chemical reagents can cause secondary pollution.It is imperative to seek cost-effective and green remediation technologies for contaminated soil.This study uses cadmium-resistant and phosphorus-dissolving microorganisms to strengthen phytoremediation of heavy metal contaminated soil.This method is not only low in cost,widely used,and will not cause secondary pollution,but also can increase the content of available phosphorus in the soil.Therefore,it has greater theoretical significance.And practical application value.Collect the rock weathered soil(RWS)sample from the dump in the Fushun West Open-pit Mine,and isolated and purified the cultivable bacteria in it,and obtained 5 strains.By observing the individual morphology and colony characteristics of the strains,detecting the 16S rDNA gene sequence,analyzing the physiological and biochemical characteristics and other multi-phase classification methods,the species was identified.The results showed that the OS1 is Pseudomonas songnenensis,LNY5 is Pseudomonas stutzeri,MZ1 is Acinetobacter radioresistens,MZ2 is Bacillus mycoides group,MF2 is Paenarthrobacter sp.and MF1 is Bacillus megaterium.Through domestication experiments,the tolerance of bacteria to heavy metal Cd2+was investigated,and it was found that strains MZ1,MZ2 and MF2 had different tolerance to heavy metal Cd2+.MZ2 had the highest tolerant to heavy metal Cd2+,which is 100.00mg/L.The tolerance of MZ1 to heavy metal Cd2+is 50.00mg/L,and the tolerance of MF2 to Cd2+is only 10.0Omg/L.Taking the changes of superoxide dismutase(SOD),catalase(CAT),proline and soluble protein content in bacteria under Cd2+stress conditions as indicators,the physiological response mechanism of strains MZ1 and MZ2 to Cd2+stress was explored.The results showed that low concentration of Cd2+can increase the SOD activity of MZ2,but when it reached a certain concentration,SOD activity gradually decreased.Cd2+ stress had an inhibitory effect on the SOD activity of MZ1.MZ1 and MZ2 had low CAT content.The CAT content increased under low concentration stress,and decreased under high-concentration stress.With the increase of Cd2+ concentration,the soluble protein content of MZ2 decreased at first,then increased and then gradually decreases.The soluble protein of MZ1 increased slightly at first,and then gradually decreased,but the overall content was low,only 0.00-1.60mg/L.The proline content of MZ2 showed an overall downward trend,and slightly increased when Cd2+ was 30.00 mg/L.The proline content of MZ1 increased slightly at low concentrations,and then gradually decreased.The phosphorus solubilizing ability of 5 strains of bacteria was investigated,and the study found that the strains MZ1,MZ2 and MF2 can effectively dissolve calcium phosphate.Among them,the amount of dissolved phosphorus of MZ2 reached the highest at 96h,which was 55.48 mg/L.The ability of MZ1 to dissolve phosphorus was weak,and the amount of dissolved phosphorus at 120h was only 5.79 mg/L.The amount of dissolved phosphorus of MF2 reached the highest at 72h,which was 71.76mg/L.By further exploring the mechanism of phosphate solubilization of Cd-resistant strain MZ2,and found that MZ2 had different phosphate solubilization ability under the stress of different concentrations of Cd2+.With the increase of Cd2+ concentration,the amount of phosphorus solubilized first increased and then decreased.Compared with the control group,when Cd2+ was present in the fermentation broth,the phosphorus solubilization ability of MZ2 was inhibited,and when Cd2+ reached a certain concentration,the presence of Cd2+ can promote the phosphorus solubilization ability of MZ2.The result of a small-scale experimental study on the restoration of the rock and soil of the cadmium-contaminated mining area with amphibians showed that adding different proportions of cadmium-resistant and phosphorus-dissolving bacteria had more significant effects on plant growth,plant absorption of cadmium,soil enzyme activity,soil fertility and microbial community characteristics.The addition of inoculants can significantly promote plant growth.When the inoculum inoculation amount was 5.0%(m/m),the plant growth condition was the best,and the available phosphorus and enzyme activity in the soil were greatly improved.The diversity of soil microbial communities has increased significantly.Thiobacillus,which has the effects of sulfur oxidation and phosphate dissolution,is the dominant strain.Compared with the blank control group,the removal effect of amphibians on Cd in the soil was significant,with a removal rate of 46.31%.When 5.0%and 7.0%inoculants were added,the removal rates of amphibians on soil Cd were 33.96%and 35.03%respectively.When 3.0%inoculum was added,the effect on the removal of Cd from the soil by amphibians is not obvious,which was 14.09%.This research provides a certain theoretical basis and technical parameters for the ecological restoration of the rock and soil of the open-pit coal mine dump.