SUMMARY

The death-rate of washed exponential phase Aerobacter aerogenes chilled in saline phosphate buffer (pH 6.5) at 0 " was increased by ribonuclease (RNase) but not by deoxyribonuclease, trypsin, pepsin or lysozyme; none of these enzymes had any immediate effect on theviability of similar bacterial suspensions at 20". Leakage products from chilled A. aerogenes, Mg2+ and, to a smaller extent, 0.3~-sucrose, antagonized the lethal effect of RNase on chilled organisms. RNA degradation occurred when bacteria were chilled and then incubated in fresh diluent at 37"; organisms exposed to RNase during chilling degraded RNA a t 20-25 " when the rate of auto-degradation of RNA was low. As the salt content of the environment was decreased, the amount of RNase adsorbed by the bacteria and its lethal effect increased a t both 0 " and 20"; in distilled water RNase was more lethal a t 20 " than a t 0'. Anilino-naphthalene-8-sulphonate penetrated into bacteria chilled in buffer containing this dye. Acid or alkali accelerated the death rate of bacteria to greater extents at 0 " than at 20". RNase increased the lethal effect of freezing and thawing on a population from a continuous culture and augmented subsequent degradation of RNA