Fig. 4

Biosynthesis of methionine by E. coli ΔmetAB complemented with metY/X pairs. WT and complemented E. coli ΔmetAB were grown in a minimal MOPS medium at 37 °C for 24 h, after which the cells were separated from the growth medium. The amount of methionine in each fraction was evaluated using GC-MS. (A) Intracellular methionine accumulated by WT E. coli, ΔmetAB-DG and ΔmetAB-CM, reported as μg/ml. (B) Extra-cellular methionine accumulated in the growth media by WT E. coli, ΔmetAB-DG and ΔmetAB-CM, reported as μg/ml. Peak areas were normalized to ribitol internal control, and total methionine levels were calculated according to the standard methionine calibration curves. The results are presented as means ± SD of three to four replicates for each sample. Significance between WT and the different bacterial strain was calculated according to the Student’s t-test (P < 0.05) and is identified by an asterisk. The numbers on top of the bars indicate the fold increase relative to the WT in each panel