Fig. 7. Over-expression of succinic acid transporter (sucE ) gene
and succinic acid production in fed-batch system. (A, B) The gene was
inserted onto the genomic DNA of ΔldhA-6 mutant under Psod
promoter regulation through the CRISPR/cpf1 gene editing system. (C) The
enhancement of succinic acid production was demonstrated in
[Psod:sucE- ΔldhA ] transformant (10.00 g CDW) compared toΔldhA mutant (10.94 g CDW) when using 4% hydrolysate. (D)
Comparison of the succinic acid production depending on the
concentration of hydrolysates was performed with 28~30 g
L-1 CDW of [Psod:sucE-ΔldhA ] transformant.
(E) A fed-batch system was carried out with an initial concentration of
4% hydrolysate and 30.37 g L-1 CDW of
[Psod:sucE-ΔldhA ] transformant. After 24 h of fermentation,
20 mL of 20% pine hydrolysate was added to the reaction solution,
resulting in a final concentration of the 4% hydrolysate. Acetic acid
was prone to be released during the first 9 h after feeding, while
lactic acid was measured at the later stage of the fermentation. (F) The
same volume of the 20% hydrolysate was added at 6, 9, and 24 h. P1,
Psod promoter; sucE , succinic acid transporter; T1, sacB
terminator; P2, Knr promoter; rpsL m, ribosomal
S12 protein mutant gene for streptomycin resistant; arrows, feeding.