Fig. 4

Modular engineering of PPP for succinate production. Effect of engineering a ZPG module, b RR module, and c TT module on succinate production. d Combinational utilization of optimized ZPG module (H-Zwf/M-Pgl/M-Gnd, labeled by 4-point star in a), optimized TT module (M-Tkt/H-Tal, labeled by 4-point star in c), and increased expression of SthA for succinate production. The final succinate yield in Suc-P02 is up to 1.61 mol/mol glucose, which increased by 44% over the starting strain Suc-T110 (~1.12 mol/mol). Values are the average of three biological replicates with error bars indicating one standard deviation. The 4-point star labels the best-performing succinate-producing strain during individual module engineering; the 5-point star indicates the strain with excessive expression of single module accompanied with significantly decreased succinate production. L, low expression level; M, medium expression level; H, high expression level