Fig 6.

Induction of fumarate respiration (A) and citrate fermentation (B) enzymes and transporters by fumarate and citrate. (A) Fumarate reductase FrdABCD (Frd) and fumarate/succinate antiporter (DcuB) are induced by fumarate (or other C₄-dicarboxylates or citrate) via DcuS/DcuR. (B) The citrate-induced transporter (CitT; citrate/succinate antiporter) and enzymes (CL, citrate lyase; Mdh, malate dehydrogenase) are shown in pink (induction by CitA/CitB) and green (induction by DcuS/DcuR). The enzymes and the carrier shown in pink are unique for citrate fermentation; the enzymes shown in green are used both in citrate fermentation and fumarate respiration. Abbreviations: Cit, citrate; Fum, fumarate; Mal, malate; OAA, oxaloacetate; Succ, succinate.