Xenorhabdus and Photorhabdus are entomopathogenic bacteria that cause septicemia and toxemia in insects. They produce secondary metabolites to induce host immunosuppression. Their metabolite compositions vary among bacterial species. Little is known about the relationship between metabolite compositions and the bacterial pathogenicity. The objective of this study was to compare pathogenicity and production of secondary metabolites of 14 bacterial isolates (species or strains) of Xenorhabdus and Photorhabdus. All bacterial isolates exhibited insecticidal activities after hemocoelic injection to Spodoptera exigua (a lepidopteran insect) larvae, with median lethal doses ranging from 168.8 to 641.3 CFU per larva. Bacterial infection also led to immunosuppression by inhibiting eicosanoid biosynthesis. Bacterial culture broth was fractionated into four different organic extracts. All four organic extracts of each bacterial species exhibited insecticidal activities and resulted in immunosuppression. These organic extracts were subjected to GC-MS analysis which predicted 182 compounds, showing differential compositions for 14 bacteria isolates. There were positive correlations between total number of secondary metabolites produced by each bacterial culture broth and its bacterial pathogenicity based on immunosuppression and insecticidal activity. From these correlation results, 70 virulent compounds were selected from secondary metabolites of high virulent bacterial isolates by deducting those of low virulent bacterial isolates. These selected virulent compounds exhibited significant immunosuppressive activities by inhibiting eicosanoid biosynthesis. They also exhibited relatively high insecticidal activities. Virulence variation between Xenorhabdus and Photorhabdus is determined by their different compositions of secondary metabolites, of which PLA2 inhibitors play a crucial role.

中文翻译：

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昆虫病原菌属 Xenorhabdus 和 Photorhabdus 的有毒次级代谢产物抑制磷脂酶 A2 以抑制宿主昆虫免疫

Xenorhabdus 和 Photorhabdus 是导致昆虫败血症和毒血症的昆虫病原菌。它们产生次级代谢物以诱导宿主免疫抑制。它们的代谢物组成因细菌种类而异。关于代谢物组成与细菌致病性之间的关系知之甚少。本研究的目的是比较致病性和次生代谢产物的 14 个细菌分离株（种或菌株）的致病性和产生的致病性致病菌和 Photorhabdus。所有细菌分离物在向 Spodoptera exigua（一种鳞翅目昆虫）幼虫注射血肠后均表现出杀虫活性，每只幼虫的中位致死剂量范围为 168.8 至 641.3 CFU。细菌感染还通过抑制类花生酸生物合成导致免疫抑制。细菌培养液被分成四种不同的有机提取物。每种细菌物种的所有四种有机提取物都表现出杀虫活性并导致免疫抑制。这些有机提取物进行了 GC-MS 分析，预测了 182 种化合物，显示了 14 种细菌分离物的不同组成。基于免疫抑制和杀虫活性，每种细菌培养液产生的次级代谢产物总数与其细菌致病性呈正相关。从这些相关性结果中，通过扣除低毒力细菌分离物的次级代谢产物，从高毒力细菌分离物的次级代谢物中筛选出70种毒力化合物。这些选定的有毒化合物通过抑制类花生酸的生物合成表现出显着的免疫抑制活性。它们还表现出相对较高的杀虫活性。Xenorhabdus 和 Photorhabdus 之间的毒力差异取决于它们不同的次级代谢产物组成，其中 PLA2 抑制剂起着至关重要的作用。