Encapsulation and immobilization of the S-layer protein of Lysinibacillus sphaericus in an alginate matrix for chromium adsorption

The S-layer proteins from several species of the Bacillaceae family, as well as the living biomass itself, have the capacity to accumulate toxic metal ions. More specifically, the adsorption of chromium is caused by protein biological activity, periplasmic biosorption and intracellular bioaccumulation mechanisms. This study was conducted to determine the chromium adsorption capacity of the S-layer protein of Lysinibacillus sphaericus and L. sphaericus strains. To enhance stability and efficiency, the S-layer protein was immobilized by entrapment in an alginate matrix, with the purpose of comparing the adsorption efficiency of the immobilized protein and the biomass. The immobilized S-layer protein adsorbed 44.33% of the total chromium (VI) (200 mg l−1) in the sample, while the non-immobilized treatments retained less than 30% of the dissolved metal. Our results show that, the S-layer protein may be considered important in the accumulation of toxic metals as well as promising and interesting for their metal adsorption intrinsic mechanism. Furthermore, its biological activity can potentially be enhanced through immobilization in an alginate matrix.