3.3 Small amounts of required amino acids in α-ketoglutarate module
The metabolism of arginine and histidine is involved in the synthesis of the intermediate α-ketoglutarate of TCA cycle (Figure 1), which also showed relatively small amounts of required supplements to restore cell growth (Figure S3). Therefore, the lower concentrations of arginine and histidine (20, 60, and 100 mg/L) were adopted to cultivated the auxotrophic strains to evaluate their roles in cell growth and FFA production (Figure 4).
his3 Δ had little impact on cell growth and FFA production, and the auxotrophic strain reached the optimal behavior of control strain in 60 mg/L of histidine. The performance of strain did not continue to improve when the concentration was further increased to 100 mg/L. Different from histidine, while supplementing 60 mg/L of arginine, the OD600 and FFA titer were only 60% and 30% of those in control strain within 48 h, respectively (Figure 4B, D). The minimal required amount of arginine was approximately 100 mg/L.