Responses of the Microbial Community Structure in Fe(II)-Bearing Sediments to Oxygenation: The Role of Reactive Oxygen Species

Responses of the microbial community structure in the subsurface to oxygen (O2) have been previously attributed to fundamental changes in microbial metabolic lifestyles. Here, we show that reactive oxygen species (ROS) produced from oxygenation of Fe­(II)-bearing sediments play an important role in the variation of the microbial community structure. Sediments sampled along a vertical redox gradient were exposed to laboratory air. After a 10 h oxygenation, the living bacteria counts in sediments at the depth of 100 cm decreased from 6.1 to 5.7 orders of magnitude, 4.39 mg/g of Fe­(II) was oxidized, and 27.6 μM hydroxyl radicals (•OH) was produced. Bacteria inactivation correlated well with •OH produced upon Fe­(II) oxygenation. Control experiments with the addition of ROS quencher and hydrogen peroxide further proved that the bacteria inactivation was induced by ROS rather than O2. 16S rRNA analysis indicated that the relative abundance of Anaerolineaceae increased from 15.4 to 29.9% but that of Nistrospiraeceae and Geobacteraceae decreased, pointing to the suppression of nitrification, denitrification, and iron respiration but promotion of organic matter degradation. These findings reveal an important but overlooked mechanism for the influence of O2 on the microbial community structure