Technology Platform from Nature: Bacterial S-Layers

Starting point of our research were radio-ecological investigations on the interaction of actinides with bacteria, recovered from uranium mining waste piles. Thereby several isolates were subsequently analyzed regarding their growth in presence of different heavy metals and their heavy metal binding properties, particularly using uranium. Some isolates show a high and selective binding for uranium, cadmium, lead, and a few other heavy metals. Interestingly, the heavy metals were immobilized on the cell surface, preventing any sustainable damage of the cell. Responsible for the binding of heavy metals outside the cell is a proteinaceous cell envelope, a so-called surface layer (S-layer). The highly ordered S-layers are often composed of identical protein monomers, that possess the ability to self-assemble into two-dimensional paracrystalline lattices. The highly regular structure of the S-layers with many pores of identical size and many regularly arranged functional groups offers good binding sites for different kinds of ions and molecules. Furthermore, the pores serve as nucleation sites for the formation of metal nanoclusters or minerals.
In consequence of the mentioned properties, detailed studies on the metal binding of bacterial S-layers were accomplished. As turned out, specific S-layers are able to bind uranium, arsenic, platinum and palladium. By immobilization of the S-layers, metal selective filter materials were developed. Furthermore, the regular structure of the S-layers can be utilized for the production of clustered metal and metal oxide nanoparticles for many different (photo)catalytic approaches, e.g. CNT synthesis, degradation of pharmaceuticals and detoxification of heavy metals. Pd, ZnO, and TiO2 nanoparticles immobilized on S-layer and/or S-layer coated industrial carriers were thusly produced and show a high catalytic activity in comparison to equally chemically produced nanoparticles. Moreover S-layers are very prospective for the development of compound specific biosensors by combining organic or inorganic fluorescence dyes with specific binding molecules.