Metabolic engineering of Escherichia coli for biosynthesis of D-galactonate.
Bioprocess and biosystems engineering
D-galactose is an attractive substrate for bioconversion. Herein, Escherichia coli was metabolically engineered to convert D-galactose into D-galactonate, a valuable compound in the polymer and cosmetic industries. D-galactonate productions by engineered E. coli strains were observed in shake flask cultivations containing 2gL(-1) D-galactose. Engineered E. coli expressing gld coding for galactose dehydrogenase from Pseudomonas syringae was able to produce 0.17gL(-1) D-galactonate. Inherent metabolic pathways for assimilating both D-galactose and D-galactonate were blocked to enhance the production of D-galactonate. This approach finally led to a 7.3-fold increase with D-galactonate concentration of 1.24gL(-1) and yield of 62.0%. Batch fermentation in 20gL(-1) D-galactose of E. coli =E2=88=86galK=E2=88=86dgoK mutant expressing the gld resulted in 17.6gL(-1) of D-galactonate accumulation and highest yield of 88.1%. Metabolic engineering strategy developed in this study could be useful for industrial production of D-galactonate. =20
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