Ubiquinone Biosynthesis over the Entire O ₂ Range: Characterization of a Conserved O ₂ -Independent Pathway

Abstract

In order to colonize environments with large O 2 gradients or fluctuating O 2 levels, bacteria have developed metabolic responses that remain incompletely understood. Such adaptations have been recently linked to antibiotic resistance, virulence, and the capacity to develop in complex ecosystems like the microbiota. Here, we identify a novel pathway for the biosynthesis of ubiquinone, a molecule with a key role in cellular bioenergetics. We link three uncharacterized genes of Escherichia coli to this pathway and show that the pathway functions independently from O 2 . In contrast, the long-described pathway for ubiquinone biosynthesis requires O 2 as a substrate. In fact, we find that many proteobacteria are equipped with the O 2 -dependent and O 2 -independent pathways, supporting that they are able to synthesize ubiquinone over the entire O 2 range. Overall, we propose that the novel O 2 -independent pathway is part of the metabolic plasticity developed by proteobacteria to face various environmental O 2 levels.