Intracellular folic acid concentration. (A) Folic acid concentration in E. coli BL21(DE3)ΔabgTΔpabA double knockout cells expressing YdaH were reduced in comparison with cells transformed with the empty vector. When transformed with plasmid expressing the mutant transporter, D180A, W400A, P418A, or D429A, folic acid production was increased in these cells. Each bar represents the mean of three separate cultures. (B) Folic acid concentration in E. coli BL21(DE3)ΔabgTΔpabA double knockout cells expressing MtrF were reduced in comparison with cells transformed with the empty vector. When transformed with plasmid expressing the mutant transporter, D193A, W420A, P438A, or D449A, folic acid production was increased in these cells. Each bar represents the mean of three separate cultures.