Study On Screening Of Cadmium-dissolving Microorganisms And Its Growth-Promotion Properties

In agricultural areas,cadmium pollution is one of the most common pollution and has become a serious environmental problem in many countries.Although the physical and chemical remediation technology was quick to repair,it has high costs and was likely to cause secondary pollution.Phytoremediation technology has attracted attention because of its advantages of low cost,environmental friendliness,and in-situ remediation.However,long plant growth cycles and low biomass were easily affected by the soil environment and the availability of heavy metals,resulting in unsatisfactory phytoremediation.Therefore,microbiology assists phytoremediation became a feasible measure.Microorganisms used metabolic hormones to promote the growth of plants,excreted metabolites such as organic acids to activate heavy metals in the soil,increased the bioavailability of heavy metals,and dissolved insoluble phosphorus in soils.Potassium promoted the absorption of nutrients by plants,thereby increasing plant growth and absorption of heavy metals.Different strains have different ability to activate heavy metals and promote growth.Therefore,the paper selected cadmium-tolerant bacteria from heavy metal-contaminated soils,studied the solvency of these strains on insoluble heavy metals,the adsorption efficiency among different strains,and researched the acid production ability and growth-promoting ability of strains with strong cadmium-dissolving ability.Characteristics,with a view to get both the ability to dissolve cadmium,but also have the ability to promote the ability of the bacteria,for plant-microbial recovery of bacterial fertilizer to provide scientific basis.The strains were screened from the 8 sampling soil,and the bacteria were screened using a low-phosphorus nitrogen-containing medium containing heavy metal cadmium,and 28strains were isolated.Six strains were isolated from river sediments?KS?in the downstream of the tungsten mine.Six strains were isolated from the rhizosphere soil?MT?of E.angustifolia and 8 strains from the rhizosphere soil?MJ?.Six strains were isolated from Equisetum rhizome soil?MZ?,and two strains were isolated from slag?KZ?.These 28strains grew well on plates containing 100 mg/L of Cd²⁺.The effects of 28 strains on the dissolution of cadmium carbonate and the adsorption capacity of cadmium in solution were studied.The results showed that there were 13 strains with strong solvency for cadmium carbonate,with a cadmium dissolution rate higher than60%and cadmium in the fermentation broth.Content above 400 mg/L.These 13 strains were isolated and screened from the rhizosphere soil,they were MZ9,MZ10,MZ11,MZ12,MZ13,MZ14,MT18,MT19,MT20,MJ21,MJ22,MJ25,and MJ27.The 13 strains had lower adsorption efficiency of cadmium than 50.%,in which MZ12,MZ13 and MZ14have lower cadmium adsorption rate than 10%.13 strains can keep Cd2+free in the fermentation broth and have low cadmium adsorption capacity.The 13 strains of cadmium-solubilizing bacteria produced organic acids.The test results showed that the growth and metabolism of strains produced acid to lower the pH of the culture solution.Thirteen cadmium-dissolving strains were able to secrete oxalic acid,acetic acid and citric acid.In addition,tartrate-secreting strains were MJ21,MJ22,MJ25,and MJ27,lactic acid-secreting strains were MT18,MT19,MZ13,and MZ14,and succinic acid-secreting strains were MZ13 and MZ14.The correlation analysis between organic acid content and cadmium dissolution rate showed that there was a significant positive correlation between the dissolution rate of oxalic acid and cadmium carbonate.The biological characteristics of the growth-promoting effect test results showed that 13strains have the ability to dissolve phosphorus and release potassium.Among them,the strain with the strongest phosphorus-solubilizing ability is MZ13,and the strain with the strongest potassium-releasing ability is MZ9;the 13 strains produce iron-producing carrier.The ability is weak,and there are 4 strains that do not have the ability to secrete iron carriers.When no tryptophan was added,7 strains could secrete IAA,and when tryptophan was added,13 strains secreted IAA,and the ability to secrete IAA was enhanced.