AUTHOR=Lee Junbeom , Lee Dae-Weon 

TITLE=Insecticidal Serralysin of Serratia marcescens Is Detoxified in M3 Midgut Region of Riptortus pedestris

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.913113

DOI=10.3389/fmicb.2022.913113

ISSN=1664-302X

ABSTRACT=<p><italic>Riptortus pedestris</italic> insect indiscriminately acquires not only the symbiotic bacterium <italic>Burkholderia insecticola</italic>, but also entomopathogens that are abundant in the soil <italic>via</italic> feeding. However, it is unclear how the host insect survives oral infections of entomopathogens. A previous study suggested that serralysin, a potent virulence factor produced by <italic>Serratia marcescens</italic>, suppresses cellular immunity by degrading adhesion molecules, thereby contributing to bacterial pathogenesis. Here, we observed that <italic>S. marcescens</italic> orally administered to <italic>R. pedestris</italic> stably colonized the insect midgut, while not exhibiting insecticidal activity. Additionally, oral infection with <italic>S. marcescens</italic> did not affect the host growth or fitness. When co-incubated with the midgut lysates of <italic>R. pedestris</italic>, serralysin was remarkably degraded. The detoxification activity against serralysin was enhanced in the midgut extract of gut symbiont-colonizing insects. The mRNA expression levels of <italic>serralysin</italic> genes were negligible in M3-colonizing <italic>S. marcescens</italic>. M3-colonizing <italic>S. marcescens</italic> did not produce serralysin toxin. Immunoblot analyses revealed that serralysin was not detected in the M3 midgut region. The findings of our study suggest that orally infected <italic>S. marcescens</italic> lose entomopathogenicity through host-derived degrading factors and suppression of serralysin.</p>