Growth of R. ferrireducens with citrate as electron donor and Fe(III) as electron acceptor. A) Possible pathways of citrate utilization: by-products differ depending on the availability of electron acceptor Fe(III). The different stoichiometries are summarized. B) R. ferrireducens is predicted to utilize a combination of different pathways during growth with limited Fe(III) availability. The numbers in red represent predicted fluxes.