Applications of S3 in α-keto acids synthesis
Considering the above results, preparative-scale transformation experiments were carried out using S3 as a whole-cell catalyst and L-Leu, L-Met, L-Val, and L-Phe as selected substrates. First, conditions were optimized in 250-mL shake flasks (Supplementary Figure 8 and 9), and 90–99% conversions were obtained. The reactions were then scaled to fit a 5-L reactor, allowing for 101.3–109.8 g/L α-keto acids to be produced from 110 g/L of the corresponding substrates, achieving 93.7–99.9% conversion rates and 101.4–202.6 g/L/d space-time yields (STY) in 12–24 h. The highest conversion was achieved using L-Leu (99.9%); it amounted to 109.8 g/L yield and 146.4 g/L/d STY. In contrast, the shortest conversion time (12 h) was achieved with L-Phe (94.6%), which also resulted in the highest STY (206.2 g/L/d), a 285.4% increase compared to Pmi LAAD (Figure 8).