AUTHOR=Ma Dongmei , Gu Hanjie , Shi Yanjie , Huang Huiqin , Sun Dongmei , Hu Yonghua 

TITLE=Edwardsiella piscicida YefM-YoeB: A Type II Toxin-Antitoxin System That Is Related to Antibiotic Resistance, Biofilm Formation, Serum Survival, and Host Infection

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.646299

DOI=10.3389/fmicb.2021.646299

ISSN=1664-302X

ABSTRACT=<p>The emergence of drug resistant bacteria is a tricky and confronted problem in modern medicine, and one of important reasons is the widespread of toxin-antitoxin (TA) systems in pathogenic bacteria. <italic>Edwardsiella piscicida</italic> (also known as <italic>E. tarda</italic>) is the leading pathogen threatening worldwide fresh and seawater aquaculture industries and has been considered as a model organism for studying intracellular and systemic infections. However, the role of type II TA systems are completely unknown in aquatic pathogenic bacteria. In this study, we identified and characterized a type II TA system, YefM-YoeB, of <italic>E. piscicida</italic>, where YefM is the antitoxin and YoeB is the toxin. <italic>yefM</italic> and <italic>yoeB</italic> are co-expressed in a bicistronic operon. When expressed in <italic>E. coli</italic>, YoeB cause bacterial growth arrest, which was restored by the addition of YefM. To investigate the biological role of the TA system, two markerless <italic>yoeB</italic> and <italic>yefM-yoeB</italic> in-frame mutant strains, TX01Δ<italic>yoeB</italic> and TX01Δ<italic>yefM-yoeB</italic>, were constructed, respectively. Compared to the wild strain TX01, TX01Δ<italic>yefM-yoeB</italic> exhibited markedly reduced resistance against oxidative stress and antibiotic, and markedly reduced ability to form persistent bacteria. The deletion of <italic>yefM-yoeB</italic> enhanced the bacterial ability of high temperature tolerance, biofilm formation, and host serum resistance, which is the first study about the relationship between type II TA system and serum resistance. <italic>In vitro</italic> infection experiment showed that the inactivation of <italic>yefM-yoeB</italic> greatly enhanced bacterial capability of adhesion in host cells. Consistently, <italic>in vivo</italic> experiment suggested that the <italic>yefM-yoeB</italic> mutation had an obvious positive effect on bacteria dissemination of fish tissues and general virulence. Introduction of a trans-expressed <italic>yefM-yoeB</italic> restored the virulence of TX01Δ<italic>yefM-yoeB</italic>. These findings suggest that YefM-YoeB is involved in responding adverse circumstance and pathogenicity of <italic>E. piscicida</italic>. In addition, we found that YefM-YoeB negatively autoregulated the expression of <italic>yefM-yoeB</italic> and YefM could directly bind with own promoter. This study provides first insights into the biological activity of type II TA system YefM-YoeB in aquatic pathogenic bacteria and contributes to understand the pathogenesis of <italic>E. piscicida</italic>.</p>