Exponentially growing cells of Escherichia coli ML-30 from batch cultures grown at I5C were subjected to cold osmotic shock. This treatment consisted of suspending cells in a hyperosmolar solution of an inert solute containing EDTA at 37°C and then in 0.5 mM MgCl2 at 0°C, This treatment caused a decrease in the initial rate of accumulation of the non-metabolisable solute methyIglucoside. An examination was made of the effects of different growth temperatures on the susceptibility of Escherichia coli to modified shock treatments and on its lipid composition. This allowed an assessment to be made of the importance of lipid unsaturation in predisposing cells to cold osmotic shock. Exponentially growing cells of Saccharomyces cerevisiae NCYG 566 from batch cultures grown at 50°C or from a chemostat culture grown under glucose limitation at 30°C were subjected to a modified form of the cold osmotic shock treatment. This treatment caused a decrease in the initial rate of accumulation of the non-metabolisable solutes glucosamine and 2-aminoisobutyrate. Storage of unshocked batch-grown yeast in buffer at 10°C led to an increase in ability to accumulate glucosamine and further experiments were confined to yeast grown in a chemostat. A study was made of the effect of modifying the cold osmotic procedure applied to yeast, including the osmotic stress, the chelating agents and the cold Mg2+ -containing diluent on viability and solute accumulating ability. Growth of shocked yeast cells in defined medium resembled that of unshocked yeast, but in malt extract-yeast extract-glucose-peptone medium the shocked yeast had a longer lag phase of growth and initially grew at a slower rate. Cold osmotic shock caused the release of low molecular- weight compounds and about 6-8% of the cell protein. The yeast cell envelope enzymes, invertase, acid phosphatase and L-leucine-naphthylamidase were not released when yeast cells were subjected to cold osmotic shock; nor was the cytoplasmic enzyme, alkaline phosphatase.
|Date of Award||1971|