Investigation of metal binding by cell wall components of Gram-positive bacteria studied by QCM-D

Investigation of the interaction of metals with the biosphere is important not only from an ecological point of view but also from an application oriented one. Biosorption of metals by bacteria was intensively studied. Furthermore, bacterial cell wall components itself e.g. surface layer (S-layer) proteins, lipids and peptidoglycan were intensively studied. Nevertheless, the investigation of their interaction with metals both as molecules and as intact layers on a molecular level remains challenging.
Parts of our investigations concentrated on S-layers. These are the outermost cell envelope of many eubacteria and archaea, forming highly ordered paracrystalline lattices not only on the cell, but also after isolation on various technical surfaces by self-assembling processes. These proteins show remarkable high metal binding capacities.
In our work we used the quartz crystal microbalance with dissipation monitoring (QCM-D) in order to study the layer formation of single cell wall compounds and interaction processes on the nano scale range. This method gives a detailed understanding of biological structure formation and the amount of metal deposition. Within the experiments the influence of surface modification with adhesive promoters e.g. polyelectrolytes was studied in order to make exact statements regarding coating kinetics, layer stability and metal interaction. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties.
Aim of these investigations is the assembly of a simplified biological cell wall based on Gram-positive bacteria in order to clarify sorption processes in a complex system.