Fig. 1
Combinatorial metabolic engineering of Bacillus subtilis for the synthesis of quercetin glycosides. (A) Biosynthetic pathway of quercetin glycosides. Glc-6-P, glucose-6-phosphate; Glc-1-P, glucose-1-phosphate; UDP-Glc, UDP-glucose; Fru-6-P, fructose-6-phosphate; UDP-GlcNAc, UDP-acetylglucosamine; Isoquercitrin, quercetin-3-O-glucoside; Q-3-GlcNAc, quercetin-3-acetylglucosamine; PgcA, glucose phosphate mutase; GtaB, glucose-1-phosphate uridyltransferase; PGI, glucose-6-phosphate isomerase; UGT78D2, UDP-glucosyltransferase. (B) Influence of engineering UDP-Glc synthesis pathway on isoquercitrin synthesis. (C) Influence of engineering UDP-Glc synthesis pathway on intracellular UDP-Glc concentration. (D) The concentration of residual quercetin. (E) Activity profiles in crude lysates of B. subtilis recombinants BSCG (initial host), BS101G (pgcA overexpressed under the control of strong constitutive promoter P43), BS102G (gtaB overexpressed under the control of strong constitutive promoter PsrfA), BS103G (pgcA and gtaB overexpressed under the control of strong constitutive promoter P43 and PsrfA, respectively)