Abstract
Bacterial growth and protein expression are impacted by nutrient balances. This study examines the effects of nutrition on growth and protein expression in green fluorescent protein (GFP)-expressing Escherichia coli BL21(DE3). When GFP-expressing E. coli was cultured in LB medium supplemented with 0.1% glucose, fructose, and maltose, GFP fluorescence intensity decreased by approximately 80% relative to control. Protein expression level was also low. In addition, the culture medium became acidified, with an increase in acetate concentration. GFP-expressing BL21(DE3) cells cultured in a low-nutrient medium with a low concentration of amino acids and carbon sources yielded reduced growth and low GFP fluorescence intensity. GFP fluorescence intensity and expression level decreased when E. coli was cultured in glucose- or fructose-supplemented low-nutrient media and the culture medium became acidified. In contrast, GFP fluorescence intensity and expression level increased in low-nutrient media supplemented with galactose and lactose.
These results demonstrate that the low pH in the culture medium results from promotion of carbohydrate metabolism and suppression of protein synthesis. Protein synthesis is inhibited in low-nutrient medium by carbohydrate metabolism induced acidification, and can be accelerated with galactose and lactose supplementation. The suppression of cell growth and protein synthesis can be ameliorated by nutrient enrichment.
