Isolation and identification of mercury-tolerant bacteria LBA119 from molybdenum-lead mining soils and their removal of Hg2+

Abstract

Aims: To screen heavy metal-tolerant strains from heavy metal-contaminated soil in mining areas and determine the tolerance of the strains to different heavy metals and their removal rates through experiments. Methods: Mercury-resistant strain LBA119 was isolated from mercury-contaminated soil samples in Luanchuan County, Henan Province, China.The strain was identified by Gram staining, physiological and biochemical tests, and 16S rDNA sequences.The LBA119 strain showed good resistance and removal rates to heavy metals such as Pb2+, Hg2+, Mn2+, Zn2+, and Cd2+ by tolerance tests under optimal growth conditions. resistance and removal rate. The mercury-resistant strain LBA119 was applied to mercury-contaminated soil to determine the ability of the strain to remove mercury from the soil compared to mercury-contaminated soil without bacterial biomass. Results: In Luanchuan County, Henan Province, soil samples contaminated with mercury were used to isolate the mercury-resistant strain LBA119. The strain was gram-negative with round bacilli but showed no spores after Gram staining, physiological and biochemical tests, and 16S rDNA sequence analysis.Under scanning electron microscopy, the size of a single bacillus was approximately 8 × 13 μm. The strain was identified as Bacillus (presumably the Bacillus megaterium strain). A study of heavy metal tolerance found that the strain was highly resistant to mercury, with a minimum inhibitory concentration (MIC) of mercury reaching 32 mg/L. Under a 10 mg/L mercury environment, the optimal inoculation amount, pH, temperature, and salt concentration of the LBA119 strain were 2%, 7, 30 °C, and 20 g/L, respectively. In the 10 mg/L Hg2+ LB medium, the total removal rate, volatilization rate, and adsorption rate at 36 h were 97.32%, 89.08%, and 8.24%, respectively. According to tolerance tests, the strain showed good resistance to Pb2+, Mn2+, Zn2+, Cd2+, and other heavy metals. When the initial mercury concentration was 50 mg/L and 100 mg/L, compared with the mercury-contaminated soil that contained LB medium without bacterial biomass, LBA119 inoculation increased 15.54-37.67% after 30 days of culture. Conclusion:This strain shows high bioremediation potential for mercury-contaminated soil.