The O ₂ -independent pathway of ubiquinone biosynthesis is essential for denitrification in <i>Pseudomonas aeruginosa</i>

Abstract

ABSTRACT Many proteobacteria, such as Escherichia coli , 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 used for reduction of dioxygen. However, this division of labor is probably not so stric. Indeed, a pathway that produces UQ under anaerobic conditions in an UbiU-, UbiV- and UbiT-dependent manner has been recently discovered in E. coli while its physiological relevance is not yet understood because of the presence of MK and DMK in this bacterium. In the present study, we established that UQ 9 is the single quinone of P. aeruginosa and that is required for growth under anaerobic respiration (denitrification). We demonstrated that ORFs PA3911, PA3912 and PA3913 , which are homologues to the E. coli ubiT, ubiV and ubiU genes, respectively, were essential for UQ 9 biosynthesis and thus for denitrification in P. aeruginosa . These three genes were hereafter called ubiT Pa , ubiV Pa and ubiU Pa . We showed that UbiV Pa accommodates a [4Fe-4S] cluster. Moreover, we demonstrated that UbiU Pa and UbiT Pa were able to bind UQ and that the isoprenoid tail of UQ was the structural determinant for the recognition by these Ubi proteins. Since the denitrification metabolism of P. aeruginosa is believed to be important for pathogenicity in cystic fibrosis patients, our results highlight the O 2 -independent UQ biosynthesis pathway as a new possible target to develop innovative antibiotics.