Abstract:The chromium-contaminated sites in plateau area were characterized by high altitude, low oxygen content and poor soil nutrients, and the isolation of indigenous high-efficiency chromium-reducing bacteria was crucial for the microbial remediation of chromiumcontaminated sites. In this study, four typical chromium-contaminated sites in plateau area were used as research objects, and the indigenous chromium-reducing bacteria were enriched and domesticated, and the tolerance of the bacteria to Cr(Ⅵ) reached more than 1600 mg/L, and the removal rate of Cr(Ⅵ) reached 71.7% after 65 d of incubation. Three single strains of highly efficient chromium-reducing bacteria were isolated from the enriched and domesticated bacterial solution, namely Leucobacter chromiireducens, Microbacterium sp. and Cellulosimicrobium sp. After 18 d of incubation, the removal rate of 300 mg/L Cr(Ⅵ) by each single bacterium reached more than 94.3%. Comparative study of the chromium reduction ability of chromium-reducing monobacteria and mixed bacteria revealed that three strains mixed bacteria had the best Cr(Ⅵ) removal effect, and the Cr(Ⅵ) removal rate increased by 35.84% after 18 d of cultivation. In view of the fact that low-cost and high-efficiency medium was often used for microbial cultivation in the process of engineering application, and the nutrient source in the engineering medium had a significant effect on the electron transfer and Cr(Ⅵ) reduction of microorganisms, this study optimized the carbon and nitrogen sources in the bacterial engineering medium on the basis of inorganic salts medium. The results showed that, with 4 g/L glucose as the carbon source and 6 g/L dried corn syrup as the nitrogen source, the chromium-reducing bacterium showed relatively excellent remediation effect, and the removal rate of Cr(Ⅵ) reached 78.46% after 18 d of cultivation.