Nitrate-driven dark oxygen production by diverse deep-sea microorganisms

To date, only three biotic pathways for light-independent oxygen production (i.e., dark oxygen) have been reported: chlorate dismutation, nitric oxide dismutation, and methanobactin-dependent water lysis. Oxygen has been shown to be produced and consumed in dark and anoxic environments, as evidenced by its prevalence in deep-sea surface sediments. However, the microbial communities and pathways driving deep-sea dark oxygen production (DOP) remain poorly understood. Here we identify a novel DOP pathway driven by dissimilatory nitrate reduction to ammonium (DNRA) in two deep-sea Deferribacterota strains. The DOP activity of these Deferribacterota strains potentially promotes the formation of manganese nodules and influences the growth and metabolism of both aerobic and anaerobic microbes, underscoring the significant role of microbial DOP in shaping deep-sea geological and ecological systems. We also cultured several deep-sea DOP-capable microorganisms from the Campylobacterota, Deinococcota, and Pseudomonadota phyla, which generate dark oxygen through unidentified nitrate-driven pathways. Combined with previous geological evidence, our results suggest that nitrate-driven dark oxygen, alongside photosynthetic oxygen, jointly contributed to early Earths oxygenation, driving the Great Oxidation Event. Overall, our findings provide novel insights into deep-sea oxygen sources, shed light on the origins of early Earths oxygen, and expand perspectives on the potential for terraforming other planets.