Chromosomally Encoded Toxin-Antitoxin System in the Fire Blight Pathogen Erwinia amylovora: Identification and Functional Characterization.

Toxin-antitoxin (TA) systems are genetic elements composed of a protein toxin and a counteracting antitoxin that is either a noncoding RNA or protein. In type I TA systems, the antitoxin is a noncoding small RNA (sRNA) that base pairs with the cognate toxin mRNA interfering with its translation. Although type I TA systems have been extensively studied in and a few human or animal bacterial pathogens, they have not been characterized in plant-pathogenic bacteria. In this study, we characterized a chromosomal locus in the plant pathogen Ea1189 that is homologous to the type I TA system previously identified in the -restricted plasmid R1. Phylogenetic analysis indicated that the chromosomal location of the locus is, thus far, unique to We demonstrated that ectopic overexpression of is highly toxic to and that the sRNA reversed the toxicity of through , a reading frame presumably translationally coupled with We also identified the region that is essential for maintenance of the main toxicity of Hok. Through a deletion mutant (Ea1189Δ), we determined the contribution of the locus to cellular growth, micromorphology, and catalase activity. Combined, our findings indicate that the TA system, besides being potentially self-toxic, provides fitness advantages to Bacterial toxin-antitoxin systems have received great attention because of their potential as targets for antimicrobial development and as tools for biotechnology. , the causal agent of fire blight disease on pome fruit trees, is a major plant-pathogenic bacterium. In this study, we identified and functionally characterized a unique chromosomally encoded toxin-antitoxin system in that resembles the plasmid-encoded copies of this system in other This study of a type I toxin-antitoxin system in a plant-pathogenic bacterium provides the basis to further understand the involvement of toxin-antitoxin systems during infection by a plant-pathogenic bacterium. The new linkage between the toxin-antitoxin system and the catalase-mediated oxidative stress response leads to additional considerations of targeting this system for antimicrobial development.