The O-independent pathway of ubiquinone biosynthesis is essential for denitrification in .

Many proteobacteria, such as , contain two main types of quinones: benzoquinones, represented by ubiquinone (UQ) and naphthoquinones, such as menaquinone (MK), and dimethyl-menaquinone (DMK). MK and DMK function predominantly in anaerobic respiratory chains, whereas UQ is the major electron carrier in the reduction of dioxygen. However, this division of labor is probably not very strict. Indeed, a pathway that produces UQ under anaerobic conditions in an UbiU-, UbiV-, and UbiT-dependent manner has been discovered recently in Its physiological relevance is not yet understood, because MK and DMK are also present in Here, we established that UQ is the major quinone of and is required for growth under anaerobic respiration ( denitrification). We demonstrate that the ORFs , , and , which are homologs of the , , and genes, respectively, are essential for UQ biosynthesis and, thus, for denitrification in These three genes here are called , , and We show that UbiV accommodates an iron-sulfur [4Fe-4S] cluster. Moreover, we report that UbiU and UbiT can bind UQ and that the isoprenoid tail of UQ is the structural determinant required for recognition by these two Ubi proteins. Since the denitrification metabolism of is believed to be important for the pathogenicity of this bacterium in individuals with cystic fibrosis, our results highlight that the O-independent UQ biosynthetic pathway may represent a target for antibiotics development to manage infections.