title: An entomopathogenic bacterium, Xenorhabdus hominickii ANU101, produces oxindole and suppresses host insect immune response by inhibiting eicosanoid biosynthesis.
abstract: An entomopathogenic bacterium, Xenorhabdus hominickii ANU101, was isolated from an entomopathogenic nematode, Steinernema monticolum. X. hominickii exhibited significant insecticidal activities at ≥6.6×102colony-forming units per larva against a lepidopteran insect, Spodoptera exigua with hemocoelic injection. The insecticidal activity of X. hominickii was reduced by an addition of arachidonic acid (AA, a catalytic product of PLA2), but enhanced by an addition by dexamethasone (DEX, a specific inhibitor of PLA2). S. exigua could defend the bacterial infection by forming hemocyte nodules. However, live X. hominickii significantly reduced the hemocytic nodulation compared to similar treatment with heat-killed X. hominickii. An addition of AA to live X. hominickii significantly rescued the immunosuppression. X. hominickii also inhibited phenoloxidase activity in hemolymph of S. exigua larvae. Furthermore, the bacteria suppressed gene expressions of antimicrobial peptides, such as attacin-1, attacin-2, defensin, gallerimycin and transferrin-1 of S. exigua. An organic extract of X. hominickii-cultured broth with ethyl acetate possessed oxindole and significantly suppressed hemocyte nodulation. Again, an addition of AA diminished the inhibitory activity of the organic extract against hemocyte nodulation. Oxindole alone inhibited hemocyte nodulation and PLA2enzyme activity. These results suggest that the entomopathogenicity of X. hominickii comes from its inhibitory activity against eicosanoid biosynthesis of target insects.
authors.affiliation: Department of Bioresource Sciences, Andong National University, Andong 36729, Republic of Korea.
authors.forename: Md
authors.initials: M
authors.lastname: Sadekuzzaman
authors.affiliation: Department of Bioresource Sciences, Andong National University, Andong 36729, Republic of Korea.
authors.forename: Youngjin
authors.initials: Y
authors.lastname: Park
authors.affiliation: Department of Bioresource Sciences, Andong National University, Andong 36729, Republic of Korea.
authors.forename: Seunghee
authors.initials: S
authors.lastname: Lee
authors.affiliation: Department of Bioresource Sciences, Andong National University, Andong 36729, Republic of Korea.
authors.forename: Kunwoo
authors.initials: K
authors.lastname: Kim
authors.affiliation: Division of Crop Cultivation and Environment Research, Department of Central Area Crop Science, National Institute of Crop Science, Rural Development Administration, Suwon 16429, Republic of Korea.
authors.forename: Jin Kyo
authors.initials: JK
authors.lastname: Jung
authors.affiliation: Department of Bioresource Sciences, Andong National University, Andong 36729, Republic of Korea. Electronic address: hosanna@anu.ac.kr.
authors.forename: Yonggyun
authors.initials: Y
authors.lastname: Kim
mesh_terms: D000818:Animals; D009348:Nematoda / Q000382:microbiology; D018411:Spodoptera / Q000276:immunology / Q000382:microbiology*; D020593:Xenorhabdus / Q000472:pathogenicity*
keywords: Eicosanoid; Immune; PLA(2); Pathogenicity; Xenorhabdus hominickii