Screening of heavy metal-resistant bacteria from the soil of road forest belt in Urumqi of China and testing of the heavy metal-removing ability

Abstract:

[Background] Heavy metal pollution of roads becomes more and more serious, and it is urgent to find efficient microbial resources for environmental remediation. [Objective] To screen heavy metal-resistant strains from the soil of road forest belt in Urumqi of China and test the heavy metal-removing ability. [Methods] Four media containing five heavy metal ions (Pb, Cd, Zn, Cu, and Ni) were used to screen the resistance strains which were then identified based on morphological characteristics and 16S rRNA gene. The removal of heavy metal ions by the strains was tested by inductively coupled plasma optical emission spectrometer (ICP-OES). [Results] Among the four media, TSA was the optimal one for the screening of strains. A total of 16 resistance strains were screened out: 4 Pb-resistant strains (tolerant concentration: 3 000 mg/L), 4 Cd-resistant strains (tolerant concentration: 800 mg/L), 4 Zn-resistant strains (tolerant concentration: 600 mg/L), 3 Cu-resistant strains (tolerant concentration: 300 mg/L), and 1 Ni-resistant strain (tolerant concentration: 400 mg/L). Among the 16 strains, the majority were Bacillus. The removal rate of 700 mg/L Pb²⁺ by strain Pb6 stood at 92.48%, and the removal rates by strains Pb11, 3 and 9 hit 27.70%, 40.37%, and 58.88%, separately. The removal rate of 200 mg/L Cd²⁺ by strain Cd4 was the highest (63.84%), and the removal rates by other Cd-resistant strains were about 30%-40%. The removal rates of 200 mg/L Zn²⁺ by strains Zn1 and Zn4 were 65.34% and 60.87%, respectively, while those by strains Zn5 and Zn6 registered 15.78% and 12.60%, separately. The removal rates of 300 mg/L Cu²⁺ by the three Cu-resistant strains were low (<3%). The removal rate of 200 mg/L Ni²⁺ by strain Ni2 was 4.31%. The strains (except for Cu1 and Cu3) mainly removed the heavy metals by adsorption, supplemented by absorption. After UV irradiation of strains Pb6, Cd4, and Zn1 for 30 s and continuous subculture, the removal rates of the corresponding heavy metals by three stable strains were 91.11%, 65.10%, and 66.48%, respectively. [Conclusion] Three strains with high tolerance to and removal rate of heavy metals were screened out: Bacillus sp. Pb6, Pseudomonas sp. Cd4, Bacillus sp. Zn1, which can be used as candidate strains for the remediation and treatment of soil or water polluted by heavy metals.