Fig. 5

Quorum-sensing (QS) regulation system in E. coli 4HPAA-△yfp. a The Esa-P_esaS QS-repressing system for automatically downregulating the expression of the pabA gene based on cell density. At low cell density, the pabA gene controlled by P_esaS expresses. At high cell densities, the pabA gene controlled by P_esaS does not express. b The Esa-P_esaR QS activation system for automatically upregulating the expression of the heterologous 4HPAA biosynthetic pathway. At low cell density, the 4HPAA biosynthetic pathway gene cluster controlled by P_esaR does not express. At high cell densities, the 4HPAA biosynthetic pathway gene cluster controlled by P_esaR expresses