Freeze-Etching of the Cell Envelope of an Acinetobacter Species Which Carries a Regular Array of Surface Subunits

Abstract

Freeze-etching was applied to preparations, with and without glycerol, of Acinetobacter sp. strain MJT/F5/199A, consisting of intact cells after normal growth or after incubation with chloramphenicol, spheroplasts, and isolated cell walls and outer membranes. Etched preparations show that a regular array of subunits forms the surface of normal cells. Near the zones of constriction in dividing cells, blebs and irregularities are seen, and some blebs, consisting of both surface subunits and outer membrane, are released from the cells. The cross-fractured cell envelope shows four layers which are related to the structures seen in section as follows: cwl, which is not visible in section, contains the surface subunits; cw2 consists of all or part of the outer membrane; cw3 includes the intermediate and dense, peptidoglycan-containing layers; within these cell wall layers is the plasma membrane. Internal fracture of the plasma membrane occurs under all conditions tested, but the fracture plane in the cell wall is only revealed in chloramphenicol-treated cells or normal cells freeze-fractured with glycerol present; the characteristic fracture faces are not seen in spheroplasts or isolated outer membranes. The concave fracture face c'w2 consists of densely packed granules, while the convex face cW3 is fibrillar. The probable location of this fracture plane is discussed. After incubation with chloramphenicol, the outer surface of the cells is obscured by extracellular material, the dense peptidoglycan-containing layer is increased in thickness, and the cytoplasm contains rounded bodies bounded by one or more unit membranes. suspending the pellet in 0.05 M phosphate buffer (pH 7.4), and adding glycerol in two equal stages, with a 1383 on July 4, 2020 by guest http://jb.asm.org/ Downloaded from 1384

Regular Array in the Cell Wall of Lactobacillus fermenti as Revealed by Freeze‐Etching and Negative Staining1

“…Occasionally the direction of the striation of the outer cell wall layer was discontinuously changed at one end of the cells. Similar observations of the directional change in the regular array were made in freeze-etched cells of Bacillus anthracis [10] and an Acinetobacter species [24]. The significance of dis continuities in the regular arrays is not known.…”

“…The outer cell wall layers with a regular array have been exposed. in some bacteria by the freeze-etching tech nique [5,10,21,[23][24][25]. To the best of our knowledge, however, the regularly ordered structure in the cell walls of lactobacilli has not yet been revealed by the technique.…”

Ultrastructure and Partial Characterization of a Regular Array in the Cell Wall of Lactobacillus brevis

“…Similar observations of the directional change in the regular arrays were made in freeze-etched cells of Acinetobacter sp. (25),Clostridium thermosaccharolyticum (28), and L. fermentum (15). We did not observe the tetragonal array in freeze-etched preparations as seen in negatively stained preparations described below, because the individual subunits of the regular array were so small that they could not be resolved in the freeze-etched cells.…”

Ultrastructure of the cell walls of two closely related clostridia that possess different regular arrays of surface subunits

“…A similar process in some gram-negative bacteria involves the formation of blebs on the outer membrane at division sites, as observed in Acinetobacter sp. (29), Escherichia coli (4), and Micrococcus radioproteolyticus (U. B. Sleytr and M. Kocur, unpublished observations).…”