Bioaccumulation characterization of cadmium by growing Bacillus cereus RC-1 and its mechanism

- Growing cells altered bioaccumulation mechanism under different Cd(II) concentrations.
- Cell morphology modifications played an important role under higher concentrations.
- Carboxyl groups were mainly involved in the Cd(II) binding.
- The efflux mechanism was responsible for reducing intracellular Cd(II) contents.
- Growing cells had high potential for the Cd(II) bioremediation.

In an effort to explore the protective mechanism of growing Bacillus cereus RC-1 against the toxicity of different Cd(II) concentrations, bacterial growth, cadmium consumption, surface interactions and intra- and extra-cellular Cd(II) contents were examined. Cellular morphology and growth were evidently affected by the initial metal concentrations above 20 mg L−1, according to the analysis of SEM, AFM, TEM and UV spectrophotometer. Surface complexation and electrostatic attraction played an important role in the different Cd(II) concentrations, as determined by the FTIR and Zeta potential analysis. Intracellular accumulation was the predominant mechanism in culture with lower metal concentrations (below 20 mg L−1), but was overshadowed by extracellular adsorption at higher concentrations. This suggested that the growing cells might employ one dominant mechanism at lower concentrations and then shift to another at higher concentrations. These results suggest options could be exploited for bioremediation of aqueous solution in which the Cd(II) concentration is less than 20 mg L−1.