Isolation of cadmium-adsorbing bacteria for soil cadmium fixation

Abstract:

[Objective] To study Cd-adsorbing bacteria for fixing soil Cd. [Methods] Tolerance of microbe against Cd was measured in the beef extract peptone liquid medium containing Cd²⁺ to select cadmium-resistant strains. The cadmium-tolerant bacteria were identified by 16S rRNA gene similarity and phylogenetic analysis, The adsorption efficiency of bacteria for Cd²⁺ was determined by adding bacteria cells into the solution containing CdCl₂. Soil culture simulation experiment was performed to analyze the effects of cadmium adsorption bacteria on cadmium-contaminated soil by determining soil pH, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, organic matter, CEC, available Cd and the number of microorganisms. [Results] Total of 57 bacteria strains isolated from the rhizosphere soil of Houttuynia cordata at Deyang showed different degrees of resistance to Cd²⁺. Three dominant Cd-resistant bacteria strains were Providencia DY8, Bacillus DY3 and Bacillus dy1-4. They showed good adsorption efficiency to Cd²⁺ in liquid. The adsorption efficiency of Cd²⁺ decreased with the Cd²⁺ concentration increasing. DY8, DY3 and DY1-4 reduced the effective Cd content in cadmium-contaminated soil by 72.11%, 68.55% and 62.32%, respectively, and significantly increased the alkali-dissolved nitrogen and available phosphorus in cadmium-contaminated soil. [Conclusion] The Cd-contaminated farmland soil contains rich resources of Cd-resistant microorganisms. Cd-absorbing bacteria can reduce the content of effective Cd in soil and improve soil nutrient conditions.

Key words:farmland soil;bacteria;cadmium adsorption;cadmium fixation