Effects of CaCl2 on viscosity of culture broth, and on activities of enzymes around the 2-oxoglutarate branch, in Bacillus subtilis CGMCC 2108 producing poly-(γ-glutamic acid)

CaCl2 was used as a novel additive to enhance poly-(gamma-glutamic acid) (7-PGA) production by Bacillus subtilis strain CGMCC 2108. Addition of CaCl2 to medium effectively reduced viscosity of culture broth, and increased consumption of extracellular glutamate by 11.4%, leading to gamma-PGA yield of 9.07 g/l, compared to 7.138 g/l in control. CaCl2 also increased activities of three key enzymes around the crucial 2-oxoglutarate branch of the gamma-PGA biosynthesis pathway: isocitrate dehydrogenase (ICDH), glutamate dehydrogenase (GDH), and 2-oxoglutarate dehydrogenase complex (ODHC). In particular, GDH activity was increased more than 8-fold, indicating that more 2-oxoglutarate was directed to synthesis of glutamate, the substrate of gamma-PGA. Interestingly, the molecular weight of gamma-PGA remained constant regardless of CaCl2 addition. (C) 2010 Elsevier Ltd. All rights reserved.