Abstract
THE lethal effect of chilling on certain exponential phase Gram-negative bacteria (‘cold shock’)1 may be due to interference with bacterial permeability control mechanisms2. Evidence supporting this view is that, on chilling, susceptible bacteria release normal endocellular constituents into the environment3 and are more permeable than similar unchilled bacteria to various substances including ribonuclease4. Cold shock also affects the stability of endogenous RNA. Thus, if susceptible bacteria are chilled and then incubated in fresh diluent at 37°, the rate of RNA-degradation increases with the duration of chilling4. In view of these symptoms of cold shock, the protection afforded to chilled bacteria by magnesium ions3 may be due to the metal's stabilizing effect on bacterial membranes concerned with osmotic control and/or endogenous RNA. In this connexion it is well known that magnesium stabilizes isolated protoplast membranes5, spheroplasts6 and ribosomes7. This note reports the use of the ‘optical effect’8 to determine the influence of magnesium on permeability control in exponential phase Aerobacter aerogenes during chilling.
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