Two NAD‐independent l‐lactate dehydrogenases drive l‐lactate utilization in Pseudomonas aeruginosa PAO1

Summary Pseudomonas aeruginosa often establishes a chronic infection in the airways of patients with cystic fibrosis (CF). l ‐Lactate is the most abundant carbon source in the CF sputum, and l ‐lactate utilization may be important for P. aeruginosa to survive in the lungs of CF patients. In this study, the key enzymes involved in l ‐lactate utilization by P. aeruginosa PAO1 were characterized using the synthetic CF sputum medium (SCFM). A highly conserved membrane‐bound NAD‐independent l ‐lactate dehydrogenase ( l ‐iLDH) encoded by lldD (PA4771) and a novel flavin‐containing membrane‐bound l ‐iLDH encoded by lldA (PA2382) were both found to contribute to l ‐lactate utilization by P. aeruginosa PAO1. In addition, an lldD and lldA double mutant was incapable of growing in a medium containing l ‐lactate as the sole carbon source. This study clarifies the mechanism and importance of l ‐lactate catabolism, and demonstrates the first Pseudomonas spp. expressing two l ‐lactate‐oxidizing enzymes.