DNA ligase Lig E increases transformation with damaged extracellular DNA

Abstract Lig E is a periplasm-targeted ATP-dependent DNA ligase found in many Gram-negative bacteria including Neisseria gonorrhoeae. Although Lig E has been shown to have a role in biofilm formation, many Lig E-possessing bacteria are also naturally competent, suggesting a possible function in transformation with extracellular DNA. Here, we demonstrate that Lig E participates in bacterial competence by increasing transformation with nuclease-damaged extracellular DNA that contains single-stranded or cohesive breaks. We show that increased transformation with this restricted DNA is ATP-dependent, and that the ATP concentration increases in the extracellular milieu during maintenance of N. gonorrhoeae in liquid culture. Impact Statement Natural transformation is an important route of horizontal gene transfer that enables competent bacteria to acquire novel phenotypic traits such as antibiotic resistance or virulence factors. By demonstrating that Lig E increases transformation of N. gonorrhoeae with damaged resistance-encoding DNA, we provide a mechanism which competent bacteria can use to overcome nucleolytic damage sustained by environmental DNA, making this more readily available as a source of novel and potentially pathogen-enhancing genes. Competing Interest Statement The authors have declared no competing interest. Abbreviations - ANOVA - Analysis of Variance - ATP - Adenosine tri phosphate - bp - base pair - CFU - colony forming units - DUS - DNA uptake sequence - EDTA - Ethylenediaminetetraacetic acid - GCB - Gonococcal base - GCBL - Gonococcal base liquid - GFP - green fluorescent protein - PCR - polymerase chain reaction