Abstract
A pET plasmid system is one of the protein expression systems used in Escherichia coli. The green fluorescent protein (GFP) exhibits green fluorescence in living cells, such as bacteria, plant cells, and mammalian cells, and thus can be used as a dye for living cells. The effect of sugars on GFP expression and the corresponding pH change were analyzed using E. coli BL21 (DE3) transformed with the pET19b vector containing gfp. The transformed E. coli was cultured on Luria-Bertani broth supplemented with glucose, galactose, fructose, maltose, lactose, sucrose, and trehalose. After 24 h cultivation, the sugars had no effect on the growth of E. coli. In the culture medium containing glucose, fructose, and, maltose, the pH decreased to 6.0
or less and the amount of GFP in E. coli was low. On the other hand, in the culture medium containing galactose, lactose, and, sucrose, the pH was 6.6 or higher and the GFP expression level increased in E. coli. Various metabolisms influence pH changes in E. coli and culture media. This result showed that pH changes due to the difference in sugar metabolism regulated the GFP expression controlled by the T7lac promoter.
