Fig. 4.

Folic acid increases E. coli folate levels via uptake of PABA-glu by AbgT. Levels of (a) 5-methyl THF-glu₃, (b) 5/10formyl THF-glu₃, (c) THF-glu₃ and (d) 5,10 methenyl THF-glu₃ in extracts of E. coli WT, ΔpabA, ΔabgT ΔpabA and ΔpabA (abgT OE) mutants supplemented with 10 μM and 100 μM folic acid. Extracts were made after 4 days of bacterial growth at 25 °C on solid agar plates. Folate counts from the LC-MS/MS were normalised by dividing by counts of an internal MTX-glu₆ spike. Error bars represent standard error of the mean of at least four replicate samples per data point (Data in Additional file 3: Table S2). Asterisks indicate test statistic of unpaired parametric t tests with Welch’s correction, where ****p < 0.0001, ***p < 0.001, **p < 0.01,*p < 0.05. Pairwise comparisons between ΔpabA and ΔabgT ΔpabA, ΔpabA (abgT OE) at 100 μM folic acid are indicated by †