Effect of Magnesium on Permeability Control in Chilled Bacteria

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.