Enhancing succinic acid production from lignocellulosic hydrolysates via reductive TCA pathway engineering in Klebsiella oxytoca
摘要
Improving the reductive tricarboxylic acid (rTCA) pathway in facultative anaerobic bacteria has important implications for efficient succinic acid (SA) production. With respective to enhance SA production from lignocellulosic hydrolysates via improving the rTCA pathway of Klebsiella oxytoca, the overexpression of phosphoenolpyruvate carboxykinase (PCK) and carbonic anhydrase (CA) genes coupling with supplementation of sodium bicarbonate (NaHCO3) were performed. The optimal concentrations of NaHCO3 supplementation for wild (WT) and engineered (RT-pck, RT-ca.) strains were determined to be 3 g/L, 1 g/L and 4 g/L, respectively. The SA production achieved by RT-pck and RT-ca. strains with respective optimal NaHCO3 supplementation reached 28.00 ± 0.33 g/L and 29.82 ± 0.35 g/L at 72 h of fermentation, resulting in the peak PCK enzyme and CA enzyme activities of 76.52 ± 6.36 pmol/(min·104 cells) and 47.06 ± 8.99 pmol/(min·104 cells), separately, as well as upregulation of several genes associated with the rTCA pathway. These findings elucidate the synergistic mechanism of pck/ca. gene overexpression and NaHCO3 supplementation in improving the rTCA pathway to enhance SA production. Overall, this study provides an effective strategy for improving lignocellulosic hydrolysate-based SA production, offering promising applications in lignocellulosic biorefinery and bioproduct process.