Identification of a novel heavy metal resistant Ralstonia strain and its growth response to cadmium exposure.

A novel Ralstonia Bcul-1 strain was isolated from soil samples that was closest to Ralstonia pickettii. Broad-spectrum resistance was identified to a group of heavy metal ions and tolerance to concentrations of Cd up to 400 mg L. Low concentrations of heavy metal ions did not have distinctive impact on heavy metal resistance genes and appeared to induce greater expression. Under exposure to Cd, cell wall components were significantly enhanced, and some proteins were also simultaneously expressed allowing the bacteria to adapt to the high Cd living environment. The maximum removal rate of Cd by the Ralstonia Bcul-1 strain was 78.97% in the culture medium supplemented with 100 mg L Cd. Ralstonia Bcul-1 was able to survive and grow in a low nutrient and cadmium contaminated (0.42 mg kg) vegetable soil, and the cadmium removal rate was up to 65.76% in 9th growth. Ralstonia Bcul-1 mixed with biochar could maintain sustainable growth of this strain in the soil up to 75 d and the adsorption efficiency of cadmium increased by 16.23-40.80% as compared to biochar application alone. Results from this work suggests that Ralstonia Bcul-1 is an ideal candidate for bioremediation of nutrient deficient heavy metal contaminated soil.