Identification of a nth-Like Gene Encoding an Endonuclease III in Campylobacter jejuni

Abstract

<p><em>Campylobacter jejuni</em> is a leading cause of foodborne illnesses worldwide. As a microaerobic pathogen, <em>C. jejuni</em> is subjected to DNA damages caused by various stresses such as reactive oxygen species (ROS) and UV radiations. The base excision repair (BER) system plays an important role in preventing mutations associated with oxidative DNA damage, but the system remains poorly characterized in <em>Campylobacter</em>. In this study, a BER homolog encoded by <em>cj0595c</em> (named <em>nth</em>) in <em>C. jejuni</em> was analyzed for endonuclease III activity and for its role in maintaining genomic stability. It was found that inactivation of <em>nth</em> resulted in elevated frequencies of spontaneous fluoroquinolone-resistant (FQR) and oxidative stress resistant (OXR) mutants, compared with the wild-type strain in <em>C. jejuni</em>. Sequencing analysis of the FQR and OXR mutants revealed that the elevated mutation rates were associated with C → T or G → A transition in <em>gyrA</em> (FQR mutants) <em>or perR</em> (for OXR mutants). In an <em>in vitro</em> assay, a purified recombinant <em>C. jejuni</em> Nth protein demonstrated endonuclease III activity that recognized and excised the thymine glycol (Tg) base from a double stranded DNA. These findings indicate that Nth functions as a BER repair enzyme in <em>C. jejuni</em> and is important for the repair of DNA damage, protecting the bacteria from stresses encountered within a host and in the environment.</p>