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Biological ceramic composites (biocers) made according to aqueous sol-gel protocol were used as selective metal binding filters. The biological component of the biocers Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile. Vegetative cells and spores of this strain are known to bind selectively U, Cu, Al, Cd, and Pb in large amounts. Sol-gel ceramics were prepared by dispersing vegetative cells, spores, and stabilized surfacelayer proteins (S-layer) in aqueous silica nanosols, gelling, and drying. The biosorption of uranium and copper by the three kinds of biocers and by their single components was investigated with dependence on time, concentration, and preparation conditions. Biocers with cells possess the highest binding capacity compared to matrixes with spores and an S-layer. Freeze-drying of prepared biocers or adding water-soluble compounds as sorbitol lead to higher porosity and faster metal binding. Uranium was bound mainly to the biological component but also to the SiO 2 network. In contrast, copper was only bound by the cells, spores, or S-layer. Bound uranium and copper were completely removed by washing with aqueous citric acid.

The functional S-layer protein gene slfB of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 was cloned as a polymerase chain reaction product into the expression vector pET Lic/Ek 30 and heterologously expressed in Escherichia coli Bl21(DE3). The addition of His tags to the N and C termini enabled the purification of the recombinant protein by Ni-chelating chromatography. The Ni binding capacity of the His-tagged recombinant S-layer protein was compared with that of the wild-type S layer. The inductively coupled plasma mass spectrometry analyses demonstrate a significantly enhanced Ni binding capability of the recombinant protein. In addition, the self-assembling properties of the purified modified S-layer proteins were studied by light microscopy and scanning electron microscopy. Whereas the wild-type S-layer proteins re-assembled into regular cylindric structures, the recombinant S-layer proteins reassembled into regular sheets that formed globular agglomerating structures. The nanoporous structure of the protein meshwork, together with its enhanced Ni binding capacity, makes the recombinant S-layer attractive as a novel self-assembling biological template for the fabrication of metal nanoclusters and construction of nanomaterials that are of technical interest.

Abstract:Microorganisms have developed various mechanisms to deal with metals, thus providing numerous tools that can be used in biohydrometallurgical processes. "Biomining" processes-including bioleaching and biooxidation processes-facilitate the degradation of minerals, accompanied by a release of metals. These processes are especially attractive for low-grade ores and are used on an industrial scale mainly for sulfidic ores. In biosorption processes, biomass or certain biomolecules are used to bind and concentrate selected ions or other molecules from aqueous solutions. Biosorptive materials can be an environmentally friendly and efficient alternative to conventional materials, such as ion exchange resins. Other interesting mechanisms are bioaccumulation, bioflotation, bioprecipitation, and biomineralisation. Although these processes are well-known and have been studied in detail during the last decades, the recent strong progress of biotechnologies (e.g., genetic engineering and molecule design), as well as their combination with novel developments in material sciences (e.g., nanotechnologies) facilitate new strategies for the application of biotechnologies in mineral processing. The article gives a summary of current activities in this field that are being performed in our group.