Figure 1.

Representation of the MEP pathway and levels of metabolites in MVA-supplemented cells.

(A) The MEP pathway simultaneously produces IPP and DMAPP for isoprenoid biosynthesis in bacteria and plant plastids. A synthetic operon that transforms exogenously supplied MVA into IPP and DMAPP allows survival of MEP-defective E. coli strains such as EcAB4-10, which lacks DXR activity. Dashed closed arrows represent several steps. GAP, glyceraldehyde 3-phosphate; DXP, deoxyxylulose 5-phosphate; MEP, methylerythritol 4-phosphate; MEcPP, methylerythritol cyclodiphosphate; IPP, isopentenyl diphosphate; DMAPP, dimethylallyl diphosphate; GGPP, geranylgeranyl diphosphate; MVA, mevalonic acid. Enzymes are shown in bold: DXS, DXP synthase; DXR, DXP reductoisomerase. Inhibitors are boxed in black: FSM, fosmidomycin; NF, norflurazon.

(B) Metabolite levels in DXR-defective EcAB4-10 cells supplemented with MVA. E. coli cells of the EcAB4-10 strain were grown in the presence of 0.5 or 10 mM MVA and collected during exponential phase (steady state) for metabolite extraction and quantification by LC-MS. Bar plots represent values of cell growth measured by optical density at 600 nm (OD₆₀₀) and intracellular levels of MVA, DXP, and IPP/DMAPP. All values are represented relative to those in 0.5-mM samples in each replicate. Dots represent individual values. Mean and standard deviation of four replicates are shown. Numbers in the plots indicate p values of Student’s t-test analyses (paired, two tailed).