| We propose to examine novel modes of bacterial oxidation of methane and ammonium, focusing on the light-independent, abiotic formation of Reactive Oxygen Species (ROS) such as hydrogen peroxide, superoxide anions, and hydroxyl radicals relevant for the early Earth. The formation of ROS precursors to molecular oxygen may have an enormous impact on life in the shallow and the deep subsurface, present and past. ROS are produced and consumed by intracellular and extracellular reactions of Fe, Mn, C, N, and S species. ROS are formed at rock surfaces by subjecting rocks to shear stresses, by weathering of igneous rocks and by (bio)transformations on iron-rich sulphide minerals (pyrite). We propose that, long before the evolution of light-dependent oxygenesis by phototrophic bacteria, ROS produced by these processes on the early Earth provided electron sinks in the metabolism of early microorganisms. We propose to examine novel modes of bacterial oxidation of methane and ammonium. ROS act as electron acceptors and provide a mechanism to activate methane and ammonium by means of oxygenases. The findings of our research will be important not only for anaerobic oxidation of methane and ammonium but also for oxygen evolution theories on Earth. Furthermore, since oxygenating radicals and methane are known to be present on Mars, our experimental results will be helpful to a better understanding of potential exobiological reactions. Our techniques will be based on sulphur isotope fractionation, tracer studies, molecular and biochemical techniques, tracer studies, use of lipid biomarkers, and growth of enrichment cultures. |
