Enhanced biosynthesis of d-tagatose from maltodextrin through modular pathway engineering of recombinant Escherichia coli
In our previous study, a whole-cell biocatalytic system involving α-glucan phosphorylase , phosphoglucomutase , glucose 6-phosphate isomerase, tagatose 1,6-bisphosphate aldolase , and phosphoglycolate phosphatase , was constructed to produce d -tagatose from maltodextrin . However, the biotransformation efficiency of this whole-cell catalyst was low because of the unbalanced ratio of each enzyme and metabolic flux of the intermediates. Therefore, in this study, the biosynthesis of d -tagatose was enhanced by optimizing vectors and improving the expression of rate-limiting enzymes through the construction of multi-copy genes to regulate expression levels. The conversion rate increased from 20.8% after 24 h to 25.2% after 3 h using 10 g/L maltodextrin as the substrate. Furthermore, the genes in the bypass pathways in Escherichia coli , pfka and zwf , were deleted to increase the accumulation of intermediates. The strain ER-2GatZ (Δ p Δ z ) produced 3.383 g/L d -tagatose using 10 g/L substrate after 3 h, which was 1.34 times that of the wild strain. This work exemplifies the use of modular engineering to enhance d -tagatose production using whole-cell catalysts.
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