oa A Novel Quinone in Nitrospirota Illuminates the Evolution of Aerobic Metabolism

The dominant organisms in modern oxic ecosystems generally rely on respiratory quinones with high redox potential (HPQs) for electron transport in aerobic metabolism. The diversification of quinones, from low redox potential in anaerobes to HPQs in aerobes, is assumed to have followed Earth’s surface oxygenation ∼2.3 billion years ago. However, the evolutionary origins of HPQs remain unresolved. Here, we characterize the structure and biosynthetic pathway of a novel HPQ, methyl-plastoquinone, that is unique to bacteria of the phylum Nitrospirota. By reconstructing the evolution of HPQs we show that aerobic metabolism using HPQs likely originated prior to Earth’s surface oxygenation.