Compatible solutes are produced by microorganisms to protect cellular structures against environmental stresses like desiccation or high salt concentrations. They are small, zwitterionic, osmotically active substances, which can accumulate at high concentrations within bacterial cells, but even at molar concentrations they do not interfere with the cellular metabolism. Here, we studied the influence of different compatible solutes on the stability of the model membrane protein bacteriorhodopsin. Mechanical characteristics of bacteriorhodopsin were measured by single-molecule atomic force spectroscopy, applying different osmolytes at varying concentrations. In the presence of ectoin higher external forces were required to unfold bacteriorhodopsin, indicating overall protein stabilization. Also, the tendency of the unfolded amino acid strand to coil up was increased, demonstrating a higher tendency for protein refolding. In summary, the stabilizing influence of the compatible solutes on the structures of the membrane proteins was clearly observed, although the compatible solutes are known to establish no direct interactions with the proteins. The effect were observed for ectoin (...more) as well as for betain and taurin (...more).
In collaboration with the group of Günther Muth (IMIT, Microbiology / Biotechnology) cover glasses with spore chains of Streptomyces sp. were imaged via an inverted optical microscope to select for hyphae at the specific stage of sporulation. The area of interest for AFM imaging was selected directly in an image of the spore chain taken by the CCD camera, using the "direct overlay" option provided in the AFM software.