Enhancing the production of poly--glutamate in Bacillus subtilis ZJS18 by the heat- and osmotic shock and its mechanism

Poly-gamma-glutamate (gamma-PGA) is a natural macromolecule peptide, and is widely used in the food, medicine, and pharmaceutical industries. In this study, heat- and osmotic shock were used to improve the production of gamma-PGA in Bacillus subtilis ZJS18, and its molecular mechanism was explored. The results indicated that the heat- and osmotic shock significantly promoted the production of gamma-PGA owing to the stress response of B. subtilis cells to adverse environment. The highest concentrations of gamma-PGA reached 14.53 and 15.98g/l under heat- and osmotic shock, respectively. The activities of five enzymes related to the metabolism of the endogenous glutamate were determined and analyzed. It was found that the activities of glucose-6-phosphate dehydrogenase, isocitrate dehydrogenase, glutamate dehydrogenase and glutamate synthase were significantly altered during heat- and osmotic shock, while the activity of alpha-ketoglutarate dehydrogenase only showed a little alteration. This study provides a basis for the industrial production and use of gamma-PGA, and for understanding its biosynthetic mechanism in B. subtilis ZJS18.