The Great Oxidation Event had a profound impact on the evolution of bioenergetics. We aim at studying how bacteria adapted their energetic metabolism to this massive change by focusing on crucial molecules: the isoprenoid quinones (hereafter simply referred to as quinones). In respiratory chains, quinones shuttle electrons and protons between proteins in the membrane. According to their mid-point redox potential, quinones can be classified as low potential (LP) such as menaquinone (MK) or high potential (HP) quinones such as ubiquinone (UQ). LP quinones are usually considered more ancient and mostly involved in anaerobic processes, whereas HP quinones are thought to have emerged to cope with rising O2 levels. We believe that quinone biosynthetic pathways have captured capital information regarding the evolution of energy metabolisms. Several pathways can lead to the production of the same quinone, and enzymes from different pathways often share homologies. Recently our group showed that UQ, a HP quinone only present in the phylum Pseudomonadota (formerly Proteobacteria) and Eukaryotes, can be synthesized not only via the classical O2-dependent pathway, but also via an extra O2-independent pathway [1]. This questions the traditional view of the roles of the quinone pathways, and their relative timing of origins. To tackle these questions we combined several bioinformatics approaches: 1) analysis of the pathways and enzymes distribution; 2) follow up of the dynamics of the pathways' genetic architecture; 3) phylogenies. Our first observations in Pseudomonadota showed a widespread distribution of the O2-independent pathway across this phylum which indicates that it could have existed in the common ancestor of UQ-producing Pseudomonadota. This would suggest that high O2 levels in the atmosphere were not a prerequisite for the emergence of UQ [1]. In addition, we recently showed that UQ produced by the O2-independent pathway can be used for anaerobic respiration (nitrate respiration in Pseudomonas aeruginosa) [2]. Our systematic investigation of quinone biosynthetic pathways across bacterial genomes allowed us to gather evidence to decipher their relative order of appearance and to get a better understanding of their respective role. This also questions the timing of appearance of HP quinones in the context of rising O2 levels. 1. L. Pelosi, C.-D.-T. Vo, S.S. Abby, L. Loiseau, B. Rascalou, M.H. Chehade, B. Faivre, M. Goussé, C. Chenal, N. Touati, L. Binet, D. Cornu, C.D. Fyfe, M. Fontecave, F. Barras, M. Lombard and F. Pierrel, mBio. (2019) 10. doi:10.1128/mBio.01319-19. 2. C.-D.-T. Vo, J. Michaud, S. Elsen, B. Faivre, E. Bouveret, F. Barras, M. Fontecave, F. Pierrel, M. Lombard and L. Pelosi, J. Biol. Chem. (2020) 295, 9021–9032. doi:10.1074/jbc.RA120.013748.