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Osmotic Reversal of Temperature Sensitivity in Escherichia coli

Department of Biology, University of Ottawa, Ottawa, Canada

ABSTRACT

Forty temperature-sensitive mutants, unable to grow on tryptone or nutrient agar at 42 C, were isolated from Escherichia coli K-12. When 0.5% NaCl was added to the medium, 32 grew at the nonpermissive temperature. Several were tested with different amounts of NaCl added to tryptone broth; all grew best when the osmolality of the medium was between 400 and 1,000 milliosmolal. One of the mutants was studied in more detail. Sucrose, inositol, KCl, and MgCl₂, as well as NaCl, permitted growth at 42 C. Glycerol, however, had no effect. When shifted from 30 to 42 C without osmotic protection, the mutant stopped growing but did not lyse, die, or leak significant amounts of intracellular material. In a similar shift experiment, a second mutant leaked all of its trichloroacetic acid-soluble pools into the medium. The majority of the mutants were hypersensitive to certain antibiotics, indicating possible cell envelope defects.