COLD SHOCK OF BACTERIA

II. MAGNESIUM-MEDIATED RECOVERY FROM COLD SHOCK AND EXISTENCE OF TWO CRITICAL TEMPERATURE ZONES IN VARIOUS BACTERIA

Abstract

Escherichia coli, Pseudomonas fluorescens, and Bacillus subtilis cells, harvested at the logarithmic phase of growth, were susceptible to cold shock as judged by their loss in viabilities. Viabilities of cold shocked cells increased rapidly upon incubation at 30° with suitable additives. Among the effective agents, magnesium ion was the most important, because no appreciable recovery in viability was observed in the absence of magnesium. When the cold shocked E. coli cells were incubated at 30° with 5×10^-3M of magnesium acetate for 10 to 20min, the viability of shocked cells became equal to that of unshocked cells. The addition of 2, 4-dinitrophenol to such systems inhibited the magnesium-mediated recovery almost completely. When NAD or ATP plus nicotinamide was further added to the reaction mixture, the inhibition by 2, 4-dinitrophenol was released. This result suggests that NAD, possibly as an energy source, is involved in the recovery process.
An increase in permeability of cold shocked E. coli cells was demonstrated with the aid of 8-anilino-1-naphthalenesulfonate. The stimulatory effect of NAD or ATP added to the reaction mixture on the recovery from the cold shock could be explained by this permeability increase.
The presence of two critical temperature zones in the cold shock was confirmed with both B. subtilis and Ps. Fluorescens. When the initial temperature of the cell suspension before the cold shock was lowered by 5°, both temperature zones moved to lower temperatures approximately by 3-5°.