Fig 4.

Extracellular reactions between NO₂⁻ and NO and mineral phase Fe(II) can contribute to NDFO. (a) Concentration of Fe(II) with synthetic vivianite as the sole Fe(II) source in NDFO cell suspensions of A. ebreus [4 mM Fe(II), 10 mM nitrate, and 0 or 5 mM acetate] in the presence of chloramphenicol. (b) Concentration of soluble Fe(II) after 15 min in cell-free basal medium containing 4 mM Fe(II) in the form of synthetic vivianite and either 1 mM sodium nitrite (NO₂⁻), 0.5 mM DEA NONOate (NO), or both compounds. Controls contained DEA and sodium hydroxide and showed no Fe(II) oxidation over the time course of the experiment. (c) Total Fe(II) concentration after 15 min and 24 h in cell-free basal medium containing 4 mM Fe(II) in the form of synthetic vivianite and either 1 mM sodium nitrite, 0.5 mM DEA NONOate (NO releasing compound), or both compounds. Controls contained DEA and sodium hydroxide and showed no Fe(II) oxidation over the time course of the experiment. Points represent averages of triplicates, and error bars represent standard deviations.