THE STRUCTURE OF THE SURFACE-LAYER OF METHANOPLANUS-LIMICOLA OBTAINED BY A COMBINED ELECTRON-MICROSCOPY AND SCANNING-TUNNELING-MICROSCOPY APPROACH

A three-dimensional surface model of the S layer of the archaebacterium Methanoplanus limicola that was obtained by a novel combination of techniques is presented. Surface-relief reconstructions of the two faces of the layer, derived from unidirectionally shadowed samples, were combined, making use of the thickness information provided by scanning tunneling microscopy. To attain as high a resolution as possible, efforts were made to minimize postdeposition changes in the metal film. To this end, the specimen was freeze-dried and tantalum/tungsten-shadowed at -80°C, transferred into the microscope at T ≤ -80°C under high-vacuum conditions, and imaged at - 175°C. At no stage was the specimen exposed to air or warmed to ambient temperature; under these conditions a stabilizing carbon-coat (C-backing), possibly obscuring fine structural detail, can be avoided. © 1994 Academic Press. All rights reserved.