Affiliation:
1. Department of Microbiology, School of Medicine and Dentistry, University of Rochester, Rochester, New York 14620
Abstract
Intact
Bacillus megaterium
cells were found to contract as much as 26% in terms of dextran-impermeable volume when transferred from water to unbuffered, non-plasmolyzing NaCl solutions. This shrinkage appeared to be primarily due to electrostatic wall contraction rather than to any osmotic response of the cells. A variety of salts (but not sucrose) added to water suspensions of isolated cell walls caused protons to be released from the walls with resultant lowering of suspension
p
H and contraction of the structures. In effect,
B. megaterium
walls behaved as flexible, amphoteric polyelectrolytes, and their compactness in aqueous suspensions was affected by changes in environmental ionic strength and
p
H. Isolated walls were most compact in low ionic strength media with a
p
H of about 4, a value close to the apparent isoelectric
p
H of wall peptidoglycan. Electrostatic attractions appeared to play a major role in determining the compactness of highly contracted walls, and the walls responded to increased environmental ionic strength by expanding. In contrast, electrostatic repulsions were dominant in highly expanded walls, and increased environmental ionic strength induced wall contraction. Walls of whole bacteria also shrank when the cells were plasmolyzed. This second type of contraction seemed to result from relief of wall tension during plasmolysis, and it could be induced with nonionic solutes. Thus, cell wall tone in
B. megaterium
appeared to be set both by mechanical tension and by electrostatic interactions among wall ions.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
130 articles.
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