Fig. 4

Extending the biosynthetic pathway from kaempferol to quercetin production. (a) Screening FMO from several plant sources to identify the best candidate by testing in MTK4 containing one copy of AtFLS. AtFMO from A. thaliana, GmFMO from Glycine max, and PhFMO from Petunia hybrida. CPR was not transferred to the strains because the background strains have already additional copy. (b) Effect of additional copies of AtFLS on quercetin production. The black circle shows the existence of the gene in the strain, instead of the white circle representing its absence. For (a) and (b), cells were cultured in a defined minimal medium in shake flask conditions, and samples were taken after 72 h of growth for quercetin, dihydrokaempferol, and kaempferol detection. c Assessing quercetin producing strains in defined minimal medium in shake flask with six discs of FeedBeads, releasing glucose slowly and constantly. Samples were taken after 96 h of growth for naringenin, dihydrokaempferol, and kaempferol measurements. Statistical analysis was performed by using one-way ANOVA, Tukey’s multiple comparison test (* < 0.05, ** < 0.01, *** < 0.001). All data represent the mean ± standard deviation of 3 biologically independent samples