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Type II toxin-antitoxin systems are essential for the survival of Erwinia amylovora under lethal stress conditions

Teja Shidore: Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station

<div>Toxin-Antitoxin systems (TAs) are ubiquitous bacterial self-killing systems comprised of an antibacterial toxin and a neutralizing antitoxin. These multi-functional systems are involved in plasmid maintenance, virulence, biofilm formation, persistence to antibiotics and other stresses. The majority of known systems are “type II” TAs, comprising of protein toxins that are suppressed by protein antitoxins. While many studies have highlighted the significance of TAs in human pathogens, not much is known about their functions in plant-associated bacteria. <em>Erwinia amylovora</em> is the causal agent of fire blight, a devastating disease of pears and apples. Genomic analysis identifies 9 putative type II TAs in <em>E. amylovora </em>strain<em> CTBT3-1.</em> We generated deletion mutants for six of these TAs and assessed their rate of survival upon prolonged log-phase exposure to streptomycin, a key antibiotic used in management of fire blight. Survival rates of individual knockout mutants were compared to the wild type using antibiotic survival assay. Deletion of the cytoskeleton-binding TAs <em>yeeUV </em>significantly reduced survival to streptomycin despite having no growth defects, suggesting a contribution to persistence to the antibiotic. Effects of either deletion or overexpression of the six TAs on virulence, biofilm formation, and survival to other stresses are also being evaluated. This study demonstrates that TAs may impact the efficacy of bacterial disease management strategies.</div>