Fig. 1.

Example of a practical genetic control strategy for an industrial bioprocess. Switch is based on depletion of sugar 1 (S1) in this example. a. In the seed tank, sugar 1 (S1) binds anti-repressor (A, results in negative control of gene expression upon substrate binding) and negatively regulates product (P) pathway associated gene expression, promoting growth. Targeted degradation of growth-associated proteins (from G) is also negatively controlled by (via repression of protease gene D). b. Prior to inoculation of the production tank, S1 is depleted to below switching threshold concentration. Without S1 bound to A, repression of both P and D is removed. Sugar 2 (S2, not a ligand for A) is used as a carbon source, P and D are expressed, and targeted proteolysis of key growth associated proteins maximizes product formation. c. Schematic illustrating trends of B and G concentrations throughout the fermentation.