Transcriptional Profiling of Type II Toxin–Antitoxin Genes of Helicobacter pylori under Different Environmental Conditions: Identification of HP0967–HP0968 System

Abstract

<i>Helicobacter pylori</i> is a Gram-negative bacterium that colonizes the human gastric mucosa and is responsible for causing peptic ulcers and gastric carcinoma. The expression of virulence factors allows the persistence of <i>H. pylori</i> in the stomach, which results in a chronic, sometimes uncontrolled inflammatory response. Type II toxin-antitoxin (TA) systems have emerged as important virulence factors in many pathogenic bacteria. Three type II TA systems have previously been identified in the genome of <i>H. pylori</i> 26695: HP0315-HP0316, HP0892-HP0893, and HP0894-HP0895. Here we characterized a heretofore undescribed type II TA system in <i>H. pylori</i>, HP0967-HP0968, which is encoded by the bicistronic operon <i>hp0968-hp0967</i> and belongs to the Vap family. The predicted HP0967 protein is a toxin with ribonuclease activity whereas HP0968 is an antitoxin that binds to its own regulatory region. We found that all type II TA systems were expressed in <i>H. pylori</i> during early stationary growth phase, and differentially expressed in the presence of urea, nickel, and iron, although, the <i>hp0968-hp0967</i> pair was the most affected under these environmental conditions. Transcription of <i>hp0968-hp0967</i> was strongly induced in a mature <i>H. pylori</i> biofilm and when the bacteria interacted with AGS epithelial cells. Kanamycin and chloramphenicol considerably boosted transcription levels of all the four type II TA systems. The <i>hp0968-hp0967</i> TA system was the most frequent among 317 <i>H. pylori</i> strains isolated from all over the world. This study is the first report on the transcription of type II TA genes in <i>H. pylori</i> under different environmental conditions. Our data show that the HP0967 and HP0968 proteins constitute a <i>bona fide</i> type II TA system in <i>H. pylori</i>, whose expression is regulated by environmental cues, which are relevant in the context of infection of the human gastric mucosa.