| Due to large scale mining of coal, oil and natural gas in northern Shaanxi province, heavy metals associated with them migrate with acidic mine water to surrounding soil, through the food chain affect human health. Because of land destruction, reclamation and many other issues faces highly technical difficulties and big challenges in Shaanxi, and there are few studies in domestic and abroad. Based on this situation, this study using the way microbiology combined with plant to repair soil polluted by heavy metals.Heavy metals Cu、Pb、Cr and Cd concentration in part of northern Shaanxi province were determined, and their existing form in soil were also examined. Based on the results, a assessment of heavy metals pollution was made. Based on the heavy metals concentration analysis, heavy metals chemical forms distribution analysis and N.L.Nemerow pollution index analysis in Coal mining area Ⅰ, Coal mining area Ⅱ, Industry zone and Maowusu demonstration zone, there is Pb light pollution in Coal mining area Ⅰ, Pb and Cd light pollution in Coal mining area I and Coal mining area Ⅱ. Besides, heavy metals exist in a higher exchangeable chemical forms in both Coal mining area Ⅰand Coal mining area Ⅱ, it means that coal mining area have great harmfulness to public society.Two phosphate-solubilizing bacterial strains were isolated from the plant root soil in Coal mining area Ⅰ and Coal mining area Ⅱ and identified as Acinetobacter calcoaceticus YC-5and Enterobacter agglomerans KMC-7based on the16S rRNA gene sequence analysis. Then through the mutation by dielectric barrier discharge (DBD), and get two mutants Acinetobacter calcoaceticus YC-5a and Enterobacter agglomerans KMC-7a. A. calcoaceticus YC-5a is less well known as phosphate solubilizing plant-associated bacteria. In this study, both A.calcoaceticus YC-5a and E. agglomerans KMC-7a produced multiple organic acids followed by a decrease in the pH of the culture medium there by solubilizing the insoluble tricalcium phosphate. The soluble phosphate production of these two strains in NBRIP medium were518.2±17.3mg1-1and435.4±15.6mg1-1, respectively. Inoculation with these two isolates were observed to significantly (p<0.05) increase the stem diameter and shoot dry weight compared to the uninoculated control. And A.calcoaceticus YC-5a showed better than E. agglomerans KMC-7a in phosphate solubilizing and plant growth promoting, though E. agglomerans KMC-7a was found to produce indole acetic acid and siderophore. The results of the study revealed that the inoculation of PSB promotes plant growth mainly by phosphate solubilizing activity, and indirectly by plant growth regulators.Response surface methodology was employed to optimize the composition of medium for phosphate solubilization by A. calcoaceticus YC-5a, which is less well known as phosphate solubilizing plant-associated bacteria.(NH4)2SO4, Ca3(PO4)2and KCl were found to have significant effects on phosphate solubilization by the Plackett-Burman design. The steepest ascent method was used to access the optimal region of the medium composition, followed by an application of response surface. The analysis revealed that the optimum values of the tested variables were (NH4)2SO40.2g/L, Ca3(PO4)212.98g/L and KCl0.49g/L, respectively. Phosphate solubilization of747.72mg/L, which was in agreement with the prediction, was observed in verification experiment. In comparison to the original level (405.4mg/L),1.83-fold increase had been obtained.A pot experiment was conducted to elucidate the effects of inoculating both strains on the growth and Pb uptake of Brassica juncea grown in different concentrations of Pb-contaminated soils. Inoculation with both PSB not only stimulated the growth of B. juncea, but it also influenced the accumulation of Pb in the shoot and root of the host plant. The present study demonstrates that PSB are a valuable microbial resource that can be exploited to improve the efficiency of phytoextraction. |
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