Optimization of cadmium adsorption conditions and anti-stress characteristics of a cadmium-tolerant Bacillus methylotrophicus strain

Abstract:

[Objective] To assess the anti-stress characteristics and to optimize the conditions affecting its cadmium ions adsorption efficiency of a cadmium-tolerant Bacillus methylotrophicus strain NTGB29. [Methods] The anti-stress characteristics were studied by plate colony-counting method. In addition, we used single factor experiment and response surface methodology to optimize the fermentation conditions of cadmium ions adsorption of the strain. Moreover, the available cadmium ions contents were used to verify the cadmium ions adsorption ability of the strain in the cadmium contaminated soils. [Results] The maximum tolerance of NTGB29 to NaCl, pH and concentration of Cd²⁺ was 10%, 11.0 and 50 mg/L, respectively. The optimum cadmium adsorption conditions were as follows:initial pH 6.4, culture temperature 37℃, NaCl concentration 4.2%, liquid volume 50 mL in the 250 mL flask, and culture time 24 h. Under the conditions, the cadmium ions adsorption percentage reached to 79.70%. In addition, the available cadmium ions of the cadmium contaminated soils was decreased significantly by adding strain NTGB29, and the adsorption percentage was 29.65%. [Conclusion] Strain NTGB29 has good environmental resistance and Cd²⁺ adsorption capacity, and it could be a kind of valuable strain source to develop the heavy metal contaminated soil conditioners and microbial functional agents.

Key words:Bacillus methylotrophicus;anti-stress characteristics;cadmium ions adsorption percentage