Xenorhabdus nematophilus inhibits p‐bromophenacyl bromide (BPB)‐sensitive PLA₂ of Spodoptera exigua

Abstract

Xenorhabdus nematophilus is a Gram-negative symbiotic bacterium of the entomopathogenic nematode, Steinernema carpocapsae. The bacteria delivered into the insect hemocoel by the nematodes cause immunodepression of the target insects to protect host nematodes and themselves from the cellular immune reaction. Previous reports suggest that the immunodepression is caused by inhibition of the eicosanoid pathway that is known to be critically important to mediate cellular immunity. This study focused on the inhibitory effect of X. nematophilus on PLA2 activity of Spodoptera exigua. The PLA2 activity was functionally associated with the activation cascade of prophenoloxidase (pPO). Dexamethasone (DEX), a specific PLA2 inhibitor, inhibited pPO activation completely at the higher doses of approximately 2.4 muM in vitro condition. The inhibitory effect of DEX was reversed by the addition of arachidonic acid, the catalytic product of PLA2. By means of this in vitro PLA2 inhibitor assay system, two different PLA2 inhibitors were used to compare their inhibitory effects on the hemolymph PLA2 of S. exigua. p-Bromophenacyl bromide (BPB), a specific inhibitor of secretory PLA2 (sPLA2), significantly inhibited pPO activation, but methylarachidonyl fluorophosphates (MAFP), a specific inhibitor of cytosolic PLA2 (cPLA2), did not show any inhibitory effect. BPB also inhibited pPO activation of the plasma, though much higher PO activation and its inhibition by BPB was found in the hemocytes. Growth medium of X. nematophilus at the stationary phase had a PLA2 inhibitory effect. Via the in vitro PLA2 inhibitor assay, it was shown that the ethyl ether extract of the medium contained significant PLA2 inhibitor activity. These results indicate that X. nematophilus produces and secretes PLA2 inhibitor, which acts on BPB-susceptible PLA2 of S. exigua.

The Global Transcription Factor Lrp Is both Essential for and Inhibitory to Xenorhabdus nematophila Insecticidal Activity

“…The bacterium Xenorhabdus nematophila is a pathogen of several insect groups and during infection overcomes insect immunity (3)(4)(5)(6)(7)(8)(9), which is comprised of two central tissues, hemocytes and fat body. Hemocytes include several types of blood cells that mediate cellular responses, such as phagocytosis and aggregation (nodulation) around a microbial invader (10).…”

“…The latter finding is based on the facts that heat-killed X. nematophila is recognized by immune surveillance systems and induces AMP expression (4,12,13) and that when wild-type X. nematophila is coinjected with an immunogenic bacterial strain it prevents induction of AMP expression (4). X. nematophila can inhibit phagocytosis and nodulation by secreting phospholipase A 2 (PLA 2 ) inhibitors (5,6,8,9,(14)(15)(16). PLA 2 catalyzes the first step in the biosynthesis of eicosanoids (17), which mediate several cellular activities, including immune signaling pathways (18).…”

A Technique to Enhance Insecticidal Efficacy Using Bt Cry Toxin Mixture and Eicosanoid Biosynthesis Inhibitor

“…일반적으 로 벡큘로바이러스 병원성은 중장을 통한 침입 이후 중장에 붙어 있는 기관지세포로 전이되어 온몸으로 전파되는 것으 로 알려지고 있다 (Washburn et al, 1995(Washburn et al, , 2001Kirkpatrick et al, 1998 (Akhurst, 1980;Kaya and Gaugler, 1993). 특별히 Xn은 감염 초기에 대상 곤충의 세포성 및 체액성 면역을 모두 억제하게 된다 (Park and Kim, 2003;Hwang et al, 2013). 이러한 Xn의 곤충 면역억 제 기작은 주로 곤충의 면역 중개물질인 아이코사노이드 생 합성을 억제하면서 나타나게 된다 (Kim et al, 2005).…”

Efficacy of an Integrated Biological Control of an Egg Parasitoid, Trichogramma evanescens Westwood, and Microbial Insecticide Against the Oriental Tobacco Budworm, Helicoverpa assulta (Guenée) Infesting Hot Pepper

“…최근에는 바이러스 침입에 대해서도 아이코사노이드류는 면역중개 역할을 하는 것 으로 보고되었으며, 이는 바이러스 침입에 대한 방어기작 으로서 페놀옥시다제(phenoloxidase: PO)의 활성이 중요 성을 갖는다는 측면에서 이해되고 있다 (Büyükgüzel et al, 2007). PO와 아이코사노이드류의 기능적 상관성이 파밤나방을 비롯한 일부 곤충류에서 보고되었다 (Park and Kim, 2003). 즉, 불활성 상태의 페놀옥시다제 전구물 질인 proPO가 PO로 활성화되는 과정에서 여러 종류의 serine proteases가 관여하게 된다 (Shrestha and Kim, 2007b).…”