Isolation of cadmium-resistant strains and preliminary study of their resistance mechanism

Abstract Six cadmium (Cd)-resistant strains, Cd-1, Cd-2, Cd-3, Cd-5, Cd-6, and Cd-7, were isolated. Cd-1, Cd-2, Cd-5, and Cd-6 were identified as Stenotrophomonas sp., Cd-3 as Achromobacter sp., and Cd-7 as Staphylococcus sp.. The six strains showed a wide adaptation range for salinity and had a strong tolerance to Cd2+. The effects of the initial Cd2+ concentration (1–100 mg/L), time (18–72 h), temperature (10–40°C), and pH (5.0–9.0) on the removal efficiency of Cd2+ were analyzed. The results revealed that the Cd2+ removal rate was higher at the initial concentrations of 5–100 mg/L than at 1mg/L. The maximum Cd2+ removal effect was found when the culture time was 36 h, the temperature was 10–35°C, and the pH was 5.0–7.0. X-ray diffraction (XRD) analysis revealed that the Cd2+ was immobilized through bio-precipitation by Stenotrophomonas sp. Cd-2 and Staphylococcus sp. Cd-7. X-ray photoelectron spectroscopy (XPS) revealed that the Cd2+ was adsorbed by Stenotrophomonas sp. Cd-2, Achromobacter sp. Cd-3, and Staphylococcus sp. Cd-7. Fourier transform infrared spectroscopy (FTIR) analysis revealed that the isolates reacted with the Cd2+ mainly through the O–H, protein N–H, C–N, lipid C–H, fatty acid COO, polysaccharide C–O, P–O, and other functional groups, as well as lipid molecules on the cell wall surfaces. Scanning electron microscopy (SEM) analysis revealed that there was little difference in the cells after Cd2+ treatment. The results of the soil remediation experiments indicate that the toxicity of Cd in soil could be effectively reduced.