Fe(Ii) Oxygenation Inhibits Bacterial Mn(Ii) Oxidation by P. Putida Mnb1 in Groundwater Under O2-Perturbed Conditions

Bacterial Mn(II) oxidation plays a crucial role in Mn cycling in natural waters and is of practical concern in the clean-up of excess Mn from drinking water. Fe(II) usually occurring together with Mn(II) in groundwater is oxidized prior to Mn(II) when perturbed by O2, but the impact of Fe(II) oxygenation on bacterial Mn(II) oxidation remains unknown. Here we demonstrated that Fe(II) oxygenation largely inhibited the Mn(II)-oxidizing ability of Pseudomonas putida MnB1. The mechanisms of the inhibition varied under different Fe(II) concentrations. At high Fe(II) concentrations (≥ 1 mM), the inhibition of bacterial Mn(II) oxidation was mainly caused by intracelluar ROS. At low Fe(II) concentrations (≤ 0.05 mM), the inhibition of bacterial Mn(II) oxidation was attributed to Fe(III) oxyhydroxides. Fe(III) oxyhydroxides attached to cell surface and damaged the cell membrane, resulting in the influx of dissolved Fe into the cell. Transcriptomic analysis revealed that the intracellular Fe suppressed the transcription initiation process and the subsequent generation of multicopper oxidases which were responsible for Mn(II) oxidation. These findings implicate that the inhibition effect of Fe(II) oxygenation on bacterial Mn(II) oxidation should be considered in groundwater-surface water interaction zone and the biological treatment of Fe-Mn containing drinking water