Biosorption of Heavy Metals by Sol-Gel Immobilized Bacillus sphaericus Cells, Spores and S-Layers

Different types of biocers were prepared by dispersing vegetative cells, spores and surface layer proteins (S-layers) of Bacillus sphaericus JG-A12 in aqueous silica nanosols, gelling or coating on glass, and drying. The enzymatic activity of embedded B. sphaericus cells depends noticeably on the water content of the biocer. The cells are destroyed by drying and shrinkage of the silica network whereas embedded spores retain their ability for germination. The biosorption of uranium and copper of these biocomposites was investigated. Biocers with cells possess the highest metal binding capacity compared to matrices with spores or S-layers. An additional increasement of the metal binding capacity is achieved by using penetration reagents like sorbitol. For renewed use biosorpted uranium and copper can be completely removed from the biocers by using aqueous citric acid. The use of spores as biocomponent offers new interesting possibilities for the preparation of storage-stable bioactive biocers.