Effects of pH and dissolved oxygen on the synthesis of γ-glutamyltranspeptidase from Bacillus subtilis SK 11.004

γ-Glutamyltranspeptidase (GGT; EC 2.3.2.2) is a widely distributed enzyme that is of interest in the food industry. In this study the effects of pH and dissolved oxygen (DO) on GGT synthesis from Bacillus subtilis SK 11.004 were investigated.

GGT production increased to 0.5 U mL⁻¹ when the pH value was controlled at 6.5. The control of a single DO level revealed that the highest specific growth rate (3.42 h⁻¹) and GGT production rate (0.40 U g⁻¹ mL⁻¹) were obtained at DO levels of 40 and 10% respectively. To satisfy the different oxygen demands at different stages of cell growth and GGT synthesis, a stage DO level control strategy was designed as follows: 40% from 0 to 4 h, 30% from 4 to 6 h and 10% from 6 to 18 h. Furthermore, the maximum biomass (2.27 g L⁻¹) and GGT production (3.05 U mL⁻¹) could be obtained using a fermentation strategy combining a constant pH value with stage DO level control.

The proposed fermentation strategy resulted in a 13.7-fold increase in GGT production. This finding should be of great importance for the industrial production of GGT.