Electron Microscopy of Archaea

Abstract

The information-processing systems of Archaea are surprisingly similar to, but much simpler than, the analogous systems in Eucarya. These similarities, discovered via genomics, indicate that the structural studies of Archaea may yield insights into the fundamental structures and mechanisms of the human branch in the tree of life. The small size of Archaea is an obstacle to their detailed structural study and generally precludes light microscopy. This chapter discusses the issues associated with the construction of three-dimensional (3D), full-cell models of a specific Archaeon at better than 10-nm resolution. Archaea must be prepared in some manner before imaging to withstand the rigors of the vacuum of the electron microscope. The two preparation technologies are either freezing alone [cryo- electron microscopy (EM)], or freezing followed by FS fixation, plastic embedding, and heavy metal staining. Cryo-EM holds the promise of structure elucidation without the artifacts that might be introduced by plastic embedding and heavy metal staining. However, at present, plastic embedding is the only technique that reproducibly allows the creation of full-cell 3D models by software-assisted segmentation.