A large series of physical techniques has been tested for the characterization of microbial cells. These techniques include gas chromatographic (GC) and high-performance liquid chromatographic (HPLC) techniques, gel electrophoresis, pyrolysis mass spectroscopy, fluorescence and chemiluminescence techniques, flow cytometry, impedance measurements, microcalorimetry, circular intensity differential scattering, nuclear magnetic resonance, and infrared as well as Raman spectroscopy (for review see Nelson, 1991). All these efforts have provided additional biochemical and structural information, which might -in some areas -be helpful for taxonomic characterizations.