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J Invertebr Pathol. 2018 Nov;159:6-17. doi: 10.1016/j.jip.2018.10.014. Epub 2018 Oct 30.

Identification of an entomopathogenic bacterium, Xenorhabdus ehlersii KSY, from Steinernema longicaudum GNUS101 and its immunosuppressive activity against insect host by inhibiting eicosanoid biosynthesis.

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Horticultural & Herbal Crop Environment Division, National Institute of Horticultural & Herbal Science, RDA, Wanju 55365, Republic of Korea.
Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea.
SM BioVision Co., Jinju 52828, Republic of Korea.
School of Environmental Ecology and Tourism, Kyungpook National University, Sangju 37224, Republic of Korea.
Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea. Electronic address:


Steinernema longicaudum GNUS101, an entomopathogenic nematode, was isolated from soils in Korea. Its internal transcribed space sequence was highly similar to the known S. longicaudum species. Infective juveniles (IJs) of S. longicaudum were highly virulent to lepidopteran and coleopteran insects. Two different bacteria were isolated from the hemolymph of lepidopteran larvae infected with S. longicaudum. They exhibited blue and red colonies on nutrient bromothymol blue agar. The red-colored bacterium was identified as Enterococcus mundtii KHY while the blue-colored bacterium was identified as Xenorhabdus ehlersii KSY based on 16S rRNA sequencing and biochemical characters. The bacterial species showed different growth rates, with X. ehlersii KSY growing more slowly than E. mundtii KHY. Both bacteria were entomopathogenic, but showed differences in suppressing host immune responses. X. ehlersii KSY, but not E. mundtii KHY, showed inhibitory activity against cellular immune responses of Spodoptera exigua larvae including hemocyte-spreading behavior and nodule formation in bacteria-cultured broth. Its immunosuppressive activity was reversed by adding arachidonic acid, an eicosanoid biosynthesis precursor. Furthermore, organic extracts of X. ehlersii KSY using hexane or ethyl acetate showed inhibitory activity against cellular immune responses of S. exigua larvae. Arachidonic acid addition to S. exigua larvae infected with X. ehlersii significantly rescued the survival rate of target insect. Of the two bacteria isolated from S. longicaudum GNUS101, only X. ehlersii induced immunosuppression of target insect by inhibiting eicosanoid biosynthesis.


Eicosanoid; Identification; Immunity; Pathogenicity; Steinernema longicaudum; Xenorhabdus ehlersii


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