46 / 2025-03-28 22:42:27

A novel quinone biosynthetic pathway in Nitrospirota illuminates the evolution of aerobic metabolism

Electron transport,quinone,respiration,great oxygenation event

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4e: Microbial Lipid Biomarkers and Their Isotopes in Environment, Biology, and Evolution

The dominant organisms in modern oxic ecosystems generally rely on respiratory quinones with high redox potential (HPQs) for electron transport in aerobic respiration and photosynthesis. 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. Nitrospirota are a metabolically diverse group that perform essential transformations in the biogeochemical cycles of nitrogen, iron, and manganese. Methyl-plastoquinone is structurally related to the two previously known HPQs, plastoquinone from Cyanobacteriota/chloroplasts and ubiquinone from Pseudomonadota/mitochondria, respectively. We demonstrate a common origin of the three HPQ biosynthetic pathways that predates the emergence of Nitrospirota, Cyanobacteriota, and Pseudomonadota. An ancestral HPQ biosynthetic pathway evolved ≥ 3.4 billion years ago in an extinct lineage and was laterally transferred to these three phyla ~2.5-3.2 billion years ago. Finally, we suggest that Cyanobacteriota and Pseudomonadota were ancestrally aerobic and thus propose that aerobic metabolism using HPQs significantly predates Earth’s surface oxygenation. Two of the three HPQ pathways were later obtained by eukaryotes through endosymbiosis forming chloroplasts and mitochondria, enabling their rise to dominance in modern oxic ecosystems.