FIG. 2.
Overexpression of branched-chain amino acid biosynthetic genes results in overproduction of isoleucine, leucine, and valine. Samples for intracellular metabolite analysis were acquired during exponential phase when cells were at steady state. Cells from strain SRB4 (ilvp+ ybgEp+ codY+), strain SRB10 (ilvp+ ybgEp+ codY), and strain SRB194 (ilvBp4 ilvBpΔT2 ybgEpΔCBS3 ilvDpΔCBS) were rapidly washed and quenched, and metabolites were extracted. Extracts were analyzed by tandem gas chromatography-time-of-flight mass spectrometry (GC-TOF). White, hatched, and gray bars denote intracellular pools of isoleucine, leucine, and valine, respectively. Asterisks denote observations statistically different relative to those for strain SRB4 (P < 0.05 by Student's two-tailed t test). Error bars indicate standard errors of the means.