STM IMAGING OF METAL-COATED CELL PLUGS OF THE ARCHAEOBACTERIUM METHANOSPIRILLUM-HUNGATEI GP1

Scanning tunnelling microscopy (STM) images of Pt/Ir- and Pt/Ir/C-coat ed cell plugs of Methanospirillum hungatei Showed paracrystalline stru ctures with P6 symmetry and an 18-nm lattice constant, in agreement wi th electron microscopy studies. The three-dimensional STM images unamb iguously distinguished the two morphologically different proteinaceous plug assemblies and led to an improved understanding of the natural i nternal organization of whole plugs. Tip convolution effects and the g rain size of the metal coating complicated interpretation of finer str uctures, We discuss possible imaging mechanisms to explain observation s in which part of the film was removed but the remaining part of the structure was still imaged reproducibly.