EFFECT OF HYPER-SALT STRESS ON THE HEAT-RESISTANCE OF A HALOTOLERANT BREVIBACTERIUM SP. JCM6894

The heat resistance of Brevibacterium sp. JCM6894 was examined as a fu nction of externally added NaCl concentrations. About a 5-log cycle re duction of the viable cell numbers was observed to result from heat tr eatment for 30 min at 47 degrees C in the absence of NaCl. When the ce lls were heated in the buffer containing 2 M NaCl, the viability was m aintained within less than 1-log cycle reduction after incubation for 30 min at 56 degrees C. During the heat treatment for 30 min at 47 deg rees C in the presence of 2 M NaCl, Na+ and K+ ions in the cells incre ased and decreased by 13 and 26 mu g ions per mg of cell protein, resp ectively. Under this condition, the amount of free amino acids in the cells changed little except for glutamate and hydroxyproline, which we re reduced by 72 and 43 nmol per mg cell protein, respectively. These results indicate that the salt stress itself and Na+ ions existing in the cytoplasm are more important factors than in vivo protein synthesi s for preventing the thermal death of the resting cells of this strain .