Fig. 3: Activity of the GED shunt in a ∆tktAB strain.

a Design of the ∆tktAB selection scheme. Xylose can be assimilated only via the GED shunt. E4P supplements are provided as the ∆tktAB strain cannot synthesize erythrose 4-phosphate. Growth on gluconate is not dependent on reductive carboxylation by Gnd and thus serves as a positive control. Reaction directionalities are shown as predicted by flux balance analysis. b Growth on xylose upon overexpression of gnd, edd, and eda (pGED) was achieved only after mutation and was dependent on elevated CO₂ concentration. Values in parentheses indicate doubling times. Curves represent the average of technical duplicates, which differ from each other by <5%. Growth experiments were repeated independently three times to ensure reproducibility. c Expression analysis by quantitative RT-PCR revealed that the transcript level of pntA increased ~3-fold in the mutated strain. Bars correspond to the average of two independent experiments, which are shown as circles. Gluconate and xylose indicate carbon sources used. d Genomic overexpression of pntAB using medium (M) or strong (S) promoter, but not weak (W) promoter, supported growth of a ∆tktAB pGED strain on xylose (legend to the left). e Deletion of glucose 6-phosphate dehydrogenase (∆zwf) supported the growth of a ∆tktAB pGED strain on xylose (legend to the left). f ¹³C-labeling experiments confirm the operation of the GED shunt. Cells were cultivated with xylose (1-¹³C) and ¹³CO₂. Observed labeling fits the expected pattern and differs from that of a WT strain cultured under the same conditions. Results from additional labeling experiments are shown in Supplementary Fig. 2. 3PG 3-phospho-glycerate, ALA Alanine, GAP glyceraldehyde-3-phosphate, GLY Glycine, HIS Histidine, PYR pyruvate, SER Serine, VAL Valine. Source data underlying b–f are provided as a Source Data file.