EFFECT OF CULTIVATION TEMPERATURES ON THERMOPHILIC AND MESOPHILIC ENZYME GENE-EXPRESSION IN BACILLUS-SUBTILIS

Expression of the thermostable neutral protease gene, nprM, from Bacillus stearothermophilus MK232 was investigated at various temperatures, using Bacillus subtilis as a host strain. When the nprM gene was expressed at temperatures of 39-degrees-C or lower, enzyme production was observed in the declining phase of batch culture. In contrast, when the cultivation temperature was higher than 40-degrees-C, enzyme production started in the exponential growth phase and continued in to the declining phase. The enzyme production was enhanced with an increase in cultivation temperature. Maximum enzyme activity per unit cell mass reached 3,500 u/OD600 at 50-degrees-C, which is twelve-fold higher than that at 30-degrees-C. When another thermostable neutral protease gene, nprT, from B. stearothermophilus CU21, was expressed in B. subtilis, enzyme production started in the exponential growth phase at 37 and 45-degrees-C. However, enzyme production decreased at higher temperatures. When B. subtilis alpha-amylase gene, amyE, was expressed in the same host cells, the enzyme production at 45-degrees-C was lower than that at 37-degrees-C. The different effects of cultivation temperature on the expression of some genes are discussed.