Genetically Programmed Control of Overflow Metabolism

Overflow metabolism is a highly undesirable phenomenon that occurs in virtually all cell factories. Although several schemes have been applied to avoid overflow metabolism, this problem remains far from being solved. In this study, a genetic sensor for detecting overflow metabolism was designed, and its substrate specificity and reversibility were demonstrated. The circuit was then used to express the small protein SgrT as an output. SgrT inhibits the main glucose transport system in E. coli, thereby reducing the glucose uptake rate. This strategy eliminated overflow metabolism in batch cultures. Furthermore, overflow metabolism was reduced by 80% when the cells were transiently exposed to excess glucose during fed-batch cultures compared to the control cells. The proposed scheme can be useful for optimizing cellular performance and dealing with heterogeneous conditions typical of large-scale bioreactors.