Isolation and identification of two chromium-tolerant bacteria and treatment of Cr(Ⅵ)-contaminated soil
To achieve high-quality microbial remediation of chromium-contaminated sites,two strains of highly chromium-resistant bacteria were isolated from soil samples near a chromate plant in North China.Based on the comparison of 16S rRNA sequences in GenBank at NCBI,strains Cr-1 and Cr-2 showed＞99％homology with Agrobacterium tumefaciens and Lysinibacillus fusiformis,respectively.The two strains were named as Agrobacterium sp.Cr-1 and Lysinibacillus sp.Cr-2,respectively.7 days after inoculation of two strains,the mass ratio of soil Cr(Ⅵ)decreased rapidly,and the Cr(Ⅵ)removal rates of Agrobacterium sp.Cr-1 and Lysinibacillus sp.Cr-2 was 94.48％and 85.12％,respectively.After 42 days'operation,the mass ratio of Cr(Ⅵ)in soil containing Agrobacterium sp.Cr-1 decreased from 1 100 mg/kg to 33.49 mg/kg,while that of Lysinibacillus sp.Cr-2 was reduced to 92.29 mg/kg.The effective reduction of high mass ratio Cr(Ⅵ)indicated two strains exhibited strong resistance to Cr(Ⅵ)and high reduction capability.Analysis of the Cr forms in soil revealed a gradual transition of Cr to Fe-Mn bound and residual states with low toxicity and bioavailability,resulting in a great reduction of its migration and biotoxicity.Bacterial diversity and metabolomics analysis of the soil after 42 days of reaction showed that the addition of both strains not only could directly participate in the Cr(Ⅵ)-reduction pathway but also promoted the growth and reproduction of chromium-reduction-related bacteria in the soil.Analysis of differential metabolites and metabolic pathways showed that both strains reduced the damage of chromium to reducing bacteria by secreting organic acids and other related substances.The reduction of Cr(Ⅵ)was achieved through the transfer of Cr from extracellular to inside through ABC transporters and metabolites related to substance transport,such as D-galactosamine,cis-4-hydroxy-D-proline,and L-pipecolic acid.This study shows that both strains can achieve efficient microbial remediation of high mass ratio hexavalent chromium-contaminated soil.
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