Isolation, identification and characterization of a Cd resistant bacterium

Abstract:

[Objective] We isolated and identified a cadmium resistant bacterium from activated sludge. Furthermore, we studied its growth characteristics and optimal biosorption conditions of Cd²⁺. This study was expected to provide strain resources and applied reference for microbial remediation of cadmium contaminated water.[Methods] The bacterium was isolated by streak plate and identified based on its 16S rRNA analysis, hemolysis testing and protein crystallization dying experiment. The growth conditions of the strain were determined by single factor test. The optimal biosorption conditions of bacterial powder were investigated by designed orthogonal experiment. Besides, the biosorption mechanisms were discussed by Scanning electron microscope (SEM), Energy Dispersive X-ray Scanning (EDS) and Fourier transform-infrared spectroscopy (FTIR) analysis. [Results] The strain was identified as Bacillus cereus and named as H6. The maximum cadmium tolerance concentration of strain H6 was 350 mg/L. Its culture conditions were:initial pH 6.0 to 8.0 at 28℃, shaking speed of 120 to 210 r/min, inoculation 1% to 5%. During the growth of strain H6, the pH of culture medium first decreased slightly and then increased gradually. The optimal biosorption conditions of bacterial powder were:dosage of 0.125 g/L, contact time of 2 h, pH 5.0 and 30℃, the biosorption capacity reached 205 mg/g. SEM-EDS and FTIR results revealed that ion exchange between Ca²⁺and Cd²⁺ occurred and the functional group of hydroxyl, carboxyl, carbonyl, amido and alkyl played a principal role during the biosorption process. [Conclusion] Strain H6, isolated from the activated sludge, was identified as Bacillus cereus with good adsorption property for Cd²⁺.

Key words:cadmium;Bacillus cereus;isolation and identification;growth condition;biosorption