Figure 1.

(a) Fine-tuning the carbon flux through modularization of gene expression. Module A, B and C are responsible for the production of intermediate A, B, and C, respectively. The accumulation of toxic intermediate B can be minimized by tuning the expression level of every module. (b) Dynamic regulation for decoupling cell growth and production. At initial stage, the cell can utilize most of resources to grow, with only a limited concentration of product accumulating. As fermentation proceeds, the accumulation of product will activate the inhibition on competing pathways and cell growth, redirecting carbon fluxes and other sources to synthesis of target compounds. (c) Growth-driven production. For example, all major source of pyruvate is removed except the one in L-Trp synthesis. Thus, the L-Trp production will become obligatory for cell growth and biomass generation based on pyruvate. (d) Product-addiction strategy. An essential gene was removed in genome and another copy is placed under the control of a product-inducible biosensor, so only the cells that are able to synthesize the target product will be able express the essential gene and survive.