Enhancement of fructose utilization from sucrose in the cell for improved l-serine production in engineered Corynebacterium glutamicum

Microbial fermentative production of l-serine has attracted increasing attention, and in our previous study, Corynebacterium glutamicum-SYPS-062ΔSSA has been successfully screened and engineered to produce l-serine from sucrose. It was noticed that there was significant fructose accumulation during l-serine fermentation process using sucrose as substrates, which is the preferred carbon resource for this strain. Lack of fructokinase may be responsible for poor fructose utilization. In the present study, a shortcut pathway for fructose utilization has been constructed via heterologous expression of scrK (fructokinase). Furthermore, pfkA (phosphofructokinase) was over-expressed to avoid over accumulation of fructose-6-phosphate, the resulting strain showed significantly improved cell growth and l-serine accumulation. In a 5-L bioreactor, the engineered C. glutamicum strain produced 30.6 g/L l-serine (0.99 mol/mol sucrose yield, with a theoretical maximal yield of 4 mol/mol sucrose), whereas the reference strain produced 20.54 g/L l-serine (with a yield of 0.67 mol/mol sucrose) at 120 h. After two feedings of sucrose, the l-serine production increased up to 37.0 g/L at 96 h.