Comprehensive evaluation and selection of the potential complex medium for industrial glutamate decarboxylase (GAD) production by Escherichia coli

To address the need for producing large quantities of an enzyme, glutamate decarboxylase (GAD), this study evaluated the performance of the currently used complex and defined culture media in terms of biomass production, GAD yield, and byproducts accumulation, and selected the candidate(s) that could maximize the production of GAD by Escherichia coli (AS 1.505, the China General Microbiological Culture Collection Center, Beijing, China). The highest yield of the enzyme per biomass in the final broth (4 431 U/g) corresponded to the Luria Bertani medium (LBM), which was 1.16 times the second highest from the Terrific Broth medium (TBM), while the highest biomass production (4.5 g/L) was achieved in the cultivation with TBM. For the byproducts, the profiles of all the media except the TK medium displayed a distinct exponential phase after six hour cultivation with a rapid byproducts generation, which could be attributed to the mixed acid fermentation caused by oxygen limitation. In addition, the subsequent re-assimilation of acetate could reduce the loss of GAD accumulated by stabilizing the media pH. The comprehensive analysis showed that although the highest biomass production was achieved by TBM, the fastest intracellular accumulation of GAD occurred in the cultivation with LBM (184.64 U/(g·h)), which also was the cheapest medium (0.56$/10 ³ U). Therefore, LBM was considered the potentially competitive candidate medium for large-scale production of GAD by E. coli.