Bacteria synthesize several types of isoprenoid quinones that are key components in electron transfer chains. The widely distributed menaquinone (MK) is typically associated with anaerobic metabolism, whereas ubiquinone (UQ) is generally considered an aerobic quinone. In addition to the classical UQ biosynthetic pathway that requires O2, we discovered an O2-independent pathway that depends on three genes ubiT, ubiU and ubiV 1. In Pseudomonas aeruginosa, these genes are essential for denitrification under anaerobic conditions 2. We have recently shown that the O2-sensing transcription factor FNR controls the expression of ubiT, ubiU and ubiV, which contribute to the development of E. coli in the mouse intestine 3. We also demonstrate that UbiU and UbiV are O2-independent hydroxylases that use an organic molecule as oxygen donor 4. Our large-scale analysis of quinone biosynthetic pathways in Pseudomonadota (formerly Proteobacteria) reveals a diversity of quinones and shows the predominance of UQ with a widespread but patchy distribution of the O2-independent pathway, and also the scattered presence of MK and rhodoquinone. We rationalize the distribution of quinones in Pseudomonadota by proposing a scenario for the evolution of the biosynthesis pathways since the great oxidation event  2.35 billion years ago. 1. Pelosi et al. mBio 10, e01319-19 (2019) 2. Vo et al. J Biol Chem 295, 9021–9032 (2020) 3. Arias-Cartin et al. mBio 14, e0329822 (2023) 4. Kazemzadeh et al. PNAS (accepted)