Fig. 1.

Schematic diagram showing the changes caused by adaptive laboratory evolution and the genetic engineering strategy. The cell growth and methane/oxygen consumption characteristics of the parental strain (CS strain) were improved by ALE. The succinate production performance of the mutant strain was enhanced by additional genetic engineering to enhance the TCA cycle and remove unnecessary pathways. The genes whose expression increased in CS40 comparing to CS were indicated by orange arrows. The oxidative branch of the TCA cycle and the glyoxylate pathway are indicated by the green and dashed blue lines, respectively. The following enzyme abbreviations were used: pMMO, particle methane monooxygenase; PPC, phosphoenolpyruvate carboxylase; PC, pyruvate carboxylase; CS, citrate synthase; MCL, malyl-CoA lyase; MTK, malate thiokinase; MS, malate synthase; IL, isocitrate lyase; SDH, succinate dehydrogenase; SSADH, succinate semialdehyde dehydrogenase