Analysis of the ultrastructure of archaea by electron microscopy.

The ultrastructural characterization of archaeal cells is done with both types of electron microscopy, transmission electron microscopy, and scanning electron microscopy. Depending on the scientific question, different preparation methods have to be employed and need to be optimized, according to the special cultivation conditions of these-in many cases extreme-microorganisms. Recent results using various electron microscopy techniques show that archaeal cells have a variety of cell appendages, used for motility as well as for establishing cell-cell and cell-surface contacts. Cryo-preparation methods, in particular high-pressure freezing and freeze-substitution, are crucial for obtaining results: (1) showing the cells in ultrathin sections in a good structural preservation, often with unusual shapes and subcellular complexity, and (2) enabling us to perform immunolocalization studies. This is an important tool to make a link between biochemical and ultrastructural studies.