Jin Gahyeon, Khan Falguni, Kim Yonggyun
Department of Plant Medicals, Andong National University, Andong 36729, Republic of Korea.
Insects. 2024 Sep 17;15(9):710. doi: 10.3390/insects15090710.
Entomopathogenic bacteria, classified into the genus , exhibit a dual lifestyle as mutualistic symbionts to nematodes and as pathogens to a broad range of insects. Bacterial virulence depends on toxin proteins that induce toxemia and various immunosuppressive secondary metabolites that cause septicemia. Particularly, the immunosuppressive properties of bacteria determine the variability of their insecticidal activities. This study explored the role of peptide metabolites in virulence and its variation among six bacterial strains across three species: , , and . Initially, their virulence significantly varied against a susceptible lepidopteran host, , but showed less variation against a tolerant coleopteran host, , with high median lethal bacterial doses. In , virulence was strongly correlated with bacterial growth rate and inhibitory activity against phospholipase A. Secondly, the six strains differed in the compositions of their secreted secondary metabolites, analyzed by GC-MS following ethyl acetate extraction. Notably, there was significant variation in the production of di- or tetra-peptides. Highly virulent strains commonly produced the cyclic Pro-Phe (cPF). Thirdly, the expression of non-ribosomal peptide synthetase () genes varied greatly among the strains. NRPS genes were minimally expressed in the tolerant and highly expressed in the susceptible . In , specific genes were markedly expressed in the virulent strains. Finally, cPF demonstrated potent immunosuppressive activity against the cellular and humoral responses of . The addition of cPF significantly enhanced the virulence against the tolerant . These findings suggest that immunosuppression is necessary for the pathogenicity of bacteria, wherein NRPS products play a critical role in suppressing immune-associated factors in target insects.
昆虫病原细菌被归类于 属，表现出双重生活方式，既是线虫的互利共生菌，又是多种昆虫的病原体。细菌的毒力取决于诱导毒血症的毒素蛋白和导致败血症的各种免疫抑制性次生代谢产物。特别是， 细菌的免疫抑制特性决定了其杀虫活性的变异性。本研究探讨了肽类代谢产物在毒力中的作用及其在三个物种（ 、 和 ）的六种细菌菌株间的差异。最初，它们对敏感鳞翅目宿主 的毒力差异显著，但对耐受性鞘翅目宿主 （中位致死细菌剂量高）的毒力差异较小。在 中，毒力与细菌生长速率及对磷脂酶A的抑制活性密切相关。其次，通过乙酸乙酯萃取后用气相色谱 - 质谱法分析，六种菌株分泌的次生代谢产物组成不同。值得注意的是，二肽或四肽的产生存在显著差异。高毒力菌株通常产生环丙苯丙氨酸（cPF）。第三，非核糖体肽合成酶（ ）基因的表达在菌株间差异很大。NRPS基因在耐受性 的表达最低，在敏感的 中高表达。在 中，特定的 基因在毒力菌株中显著表达。最后，cPF对 的细胞和体液反应表现出强大的免疫抑制活性。添加cPF显著增强了对耐受性 的毒力。这些发现表明免疫抑制是 细菌致病性所必需的，其中NRPS产物在抑制靶标昆虫的免疫相关因子中起关键作用。
