(A) Growth of D. propionicus with pyruvate (19.2 mM) as the electron donor and Fe(III)-citrate (50 mM) as the electron acceptor. (B) Growth with Fe(III)-oxide (100 mmol/liter) as the electron acceptor and hydrogen (101 kPa) as electron donor. (C) Growth with Fe(III)-oxide (100 mmol/liter) as electron acceptor and pyruvate (7.15 mM) as the electron donor. The results are the means of triplicate incubations. •, cell number; ○, cell number, control (no donor); ▪, Fe(II) concentration; □, Fe(II) concentration, control (no donor); ▴, pyruvate concentration; ▵, pyruvate concentration, control (no cells).