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The Journal of Cell Biology, Vol 61, 288-300, Copyright © 1974 by Rockefeller University Press

ARTICLE

FACTORS INFLUENCING THE FREQUENCY OF MESOSOMES OBSERVED IN FIXED AND UNFIXED CELLS OF STREPTOCOCCUS FAECALIS



Michael L. Higgins 1 and Lolita Daneo-Moore 1

1 From the Department of Microbiology and Immunology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140

Mesosomes of Streptococcus faecalis (American Type Culture Collection 9790) were seen about 92% less frequently in freeze fractures of unfixed cells than in freeze fractures and sections of fixed cells. This difference in frequency was not related to any period of unbalanced macromolecular synthesis induced by chemical fixation. All measured synthetic processes (DNA, RNA, and protein synthesis, and glycerol incorporation) were halted with either osmium tetroxide (OS) or glutaraldehyde fixation. That fewer mesosomes were seen in freeze fractures of unfixed cells was probably due to the difficulty of observing cross-fractured mesosomes in this organism in the unfixed state. Unfortunately, mesosomes probably preferentially cross fracture in the unfixed state and therefore are usually only observed, infrequently, in those cases where the freeze fracture follows the surface layer of a mesosomal membrane.

However, the addition of glycerol to unfixed cells, especially in the chilled state, greatly increased the frequency of observation of cytoplasmic mesosomes in freeze fractures. It is thought that glycerol, like chemical fixation, increases the number of surface-fractured mesosomes, which in turn increases the frequency of mesosome observation.

It was also observed that cellular autolysis occurring during OS fixation seemingly reduced the number of mesosomes observed in thin sections and freeze fractures of OS-fixed cells.

Submitted on March 12, 1973
Revised on November 12, 1973


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