Acetate is consumed prior to Fe(II) as an electron donor in nitrate-reducing cultures. (a) Concentrations of Fe(II), acetate, nitrate, and nitrite in NDFO cell suspensions of A. ebreus [10 mM Fe(II), 5 mM acetate, 10 mM nitrate] in the presence of chloramphenicol. Points represent averages of triplicates, and error bars represent standard deviations. (b) Fe(II) concentrations in NDFO cell suspensions of A. ebreus with 10 mM Fe(II); 10 mM nitrate; and 0, 5, or 10 mM acetate. Points represent averages of triplicates, and error bars represent standard deviations.