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Objective To screen the microbial strains capable of efficiently activating soil cadmium, addressing the technical bottleneck of low efficiency in cadmium-contaminated soil remediation by hyperaccumulators. Methods Farmland soils with potential Cd contamination were collected from various locations in Hunan Province. Acid-producing bacteria were initially screened via the bromocresol purple discoloration method. The pH of the fermentation broth, cadmium chloride tolerance, and cadmium carbonate activation capacity were compared among strains to identify dominant strains, which were then subjected to species identification. On this basis, bacterial strains with application potential were further screened. The desorption effect of the selected strain on soil cadmium under different carbon and nitrogen sources was investigated through shake flask experiments. Pot experiments were carried out to analyze the activation effect on soil cadmium under different nutrient conditions. Results A total of 372 acid-producing bacterial strains were isolated via the bromocresol purple discoloration method. Through comprehensive screening based on the ratio of the discoloration zone diameter (D) to the colony diameter (d) on solid plates, fermentation broth pH, cadmium chloride tolerance, and cadmium carbonate activation assays, four elite strains, designated HT-B1, HTQ-B1, QBS-B2, and MY-B1, were selected. They were identified as Staphylococcus epidermidis, Staphylococcus hominis, Priestia megaterium, and Acinetobacter sp., respectively, based on molecular evidence. In accordance with microbial fertilizer safety standards, strain QBS-B2 was prioritized for further study. This strain exhibited a minimum fermentation broth pH of 3.65 and achieved a cadmium carbonate activation rate of 92.27%. Culture with glucose as the carbon source and ammonium chloride as the nitrogen source were found to be optimal for enhancing cadmium desorption from soil by strain QBS-B2. Under these conditions, the soluble cadmium concentration reached 170.77 μg/L, which was 66.5 times higher than that of the control group, corresponding to a soil cadmium desorption rate of 46.21%. Furthermore, strain QBS-B2 significantly increased the content of available cadmium and available phosphorus in the soil. The application of compound fertilizer enhanced the cadmium activation of QBS-B2, resulting in a soil cadmium activation rate of 17.37%. The application of organic fertilizer significantly promoted the colonization and growth of the strain in the soil and increased the available phosphorus content by 5.9 times compared with the control. Conclusion This study provides elite microbial resources for the development of cadmium-activating microbial inoculants and bio-organic fertilizers based on P. megaterium QBS-B2. Furthermore, it establishes a theoretical foundation and demonstrates application potential for bio-augmented phytoextraction in the remediation of cadmium-contaminated soils.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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