DNA ligase LigE increases bacterial transformation with damaged extracellular DNA

LigE is a periplasm-targeted ATP-dependent DNA ligase found in many Gram-negative bacteria, including Neisseria gonorrhoeae. Although LigE has been shown to have a role in biofilm formation, many LigE-possessing bacteria are also naturally competent, suggesting a possible role in transformation with extracellular DNA. Here, we demonstrate that LigE participates in competence by increasing transformation with nuclease-damaged extracellular DNA that contains single-stranded or cohesive breaks, and that this activity is dependent on its secretion signal peptide, indicating an extra-cytoplasmic location of activity. We show that increased transformation with this restricted DNA is ATP-dependent; however, the physiological source of ATP in the natural host remains unknown. Our findings highlight a potential role of Ngo-LigE in Neisseria gonorrhoeae competence and horizontal gene transfer.