Adsorption behavior and heavy metal interaction processes of cellular components of Gram-positive bacteria investigated by QCM-D

Sorption processes based on biological materials like biomass itself or cell fragments become more and more attractive for biotechnological applications. In our group we work with isolated bacteria from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) that have high affinities for heavy metals [1]. The metal binding sites are predominantly provided by the bacterial cell wall, mainly by surface layer proteins, but also by other parts of the cell wall e.g. membrane lipids and peptidoglycan. Such biological structures and vital bacterial cells can be used to develop biosorptive materials that are of interest for a broad range of applications. Examples are bioremediation, for a specific and efficient removal and recovery of heavy, precious or actinide metals and as templates for synthesis of bio-based sensory layers or chemical catalysts [2, 3].
In our investigations surface layer proteins (S-layers) are one major research topic. They represent the outermost cell envelope of many eubacteria and archaea forming highly ordered paracrystalline lattices not only on the living cell, but also after isolation on various technical surfaces by self-assembling processes [4]. In previous work these proteins were immobilized in sol-gel ceramics for the successful removal of uranium and chromium [5, 6]. The highly ordered proteins allow a specific metal binding in the pores of the protein lattice. This property can be used for the arrangement of highly structured nanoparticles (e.g. Au, Pd, Pt). Thus investigation of the interaction of isolated cell wall components, like S-layer, peptidoglycan, lipids and secondary cell wall polymers (SCWP) or intact composites with metals and nanoparticles is important. But the deeper understanding of these processes on a molecular level remains challenging. Besides standard analytical methods the quartz crystal microbalance with dissipation monitoring (QCM-D) is used as versatile tool to track and control the biological layer formation, metal interaction and nanoparticle deposition as well as adsorption kinetics. This method allows the real time detection of sorption processes on a molecular level and gives further information of viscoelastic properties, layer stabilities and the total adsorbed mass [7]. Aim of our work is to study metal sorption behavior of cells and single cell wall fragments from Gram-positive bacteria to get more information about multilevel processes in complex natural systems. Therefore it is necessary to examine different immobilization strategies for the used biological components on various technical surfaces [8, 9]. The sorption behavior of metals and nanoparticles with the biological material will be studied by batch experiments and QCM-D [9]. The results were partially evaluated by supporting atomic force microscopy (AFM).

[1] Raff, J., Selenska-Pobell, S. (2006), Nuclear Engineering International 51 (619), 34-36.
[2] Das, N. (2010), Hydrometallurgy 105, 180-189.
[3] Pollmann, K. et al. (2006), Biotechnol. Adv. 24, 58-68.
[4] Sleytr, U. B. et al. (2007), FEMS Microbiology Letters 267(2), 131-144.
[5] Carreo, D. M. et al. (2011), The Canadian Journal of Chemical Engineering 89, 1281-1287.
[6] Raff, J. et al. (2003), Chem. Mater. 15, 240-244.
[7] Lopez, A.E. et al. (2010), Small 6 (3), 396-403.
[8] Günther, T. J., Suhr, M. et al. (2013), submitted.
[9] Suhr, M. et al. (2013), in preparation.