Analysis and engineering of the S-layer protein of Bacillus sphaericus JG-A12 and potential technological applications


Analysis and engineering of the S-layer protein of Bacillus sphaericus JG-A12 and potential technological applications

Pollmann, K.; Raff, J.; Merroun, M.; Fahmy, K.; Mikeehenko, I.; Creamer, N.; Macaskie, L.; Selenska-Pobell, S.

Uranium mining waste isolate B. sphaericus JG-A12 is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters [1]. The cells of this strain are enveloped by a surface protein layer (S-layer), which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date [2]. The highly ordered crystalline S-layers are one of the most common cell envelope structures of bacteria and archaea [3]. Most of them are composed of identical protein monomers which 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 offers good binding sites for different kinds of molecules and also nucleation sites for formation of metal nanoclusters or minerals.
We demonstrate that the purified and recrystallized S-layer of B. sphaericus JG-A12 is capable to bind effectively Pd(II) from salt solutions. EXAFS and IR spectroscopic analyses demonstrate that the Pd atoms are bound to the carboxyl groups of the S-layer. In accordance to this we found aspartate and glutamate rich stretches in the C-terminal domain of the S-layer which are possibly responsible for the deposition of Pd in the pores of the protein lattices. The deposition of Pd complexes stabilizes the protein structure. In presence of reducing agents deposited Pd is reduced to metallic nanoclusters. The latter is in agreement with the studies on another S-layer [4].
We demonstrate also that Pd nanoclusters are formed on the intact cells of B. sphaericus JG-A12 via a two step process consisting of biosorption (I) and of consequent metal reduction (II) in the presence of molecular H2 as an electron donor. The metallic nature of the clusters was confirmed by EXAFS and their size was estimated to be about 9-10 Ǻ. TEM analysis showed that the clusters are localized at specific sites of the bacterial cell wall, indicating the primary role of the S-layer in their formation. The Pd nanoclusters deposited at the cells of B. sphaericus JG-A12 show catalytic activity comparable to commercial ones.
Genetic engineering of the S-layer is applied for optimizing its capability to form Pd nanoclusters with increased catalytic activity and also in order to extend its binding capacity to other metals of industrial interest.

  • Poster
    Biotechnology 2004 - Konferenz, Santiago de Chile, 17.10.-22.10.2004
  • Poster
    2nd Max Bergmann Symposium, 17.-18.02.2005, Dresden, Deutschland
  • Contribution to proceedings
    Biotechnology 2004, 17.-22.10.2004, Santiago de Chile, Chile

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Publ.-Id: 6630