Table_2_Gut–Liver Immune Response and Gut Microbiota Profiling Reveal the Pathogenic Mechanisms of Vibrio harveyi in Pearl Gentian Grouper (Epinephelus lanceolatus♂ × E. fuscoguttatus♀).doc

Vibrio harveyi causes vibriosis in nearly 70% of grouper (Epinephelus sp.), seriously limiting grouper culture. As well as directly inhibiting pathogens, the gut microbiota plays critical roles in immune homeostasis and provides essential health benefits to its host. However, there is still little information about the variations in the immune response to V. harveyi infection and the gut microbiota of grouper. To understand the virulence mechanism of V. harveyi in the pearl gentian grouper, we investigated the variations in the pathological changes, immune responses, and gut bacterial communities of pearl gentian grouper after exposure to differently virulent V. harveyi strains. Obvious histopathological changes were detected in heart, kidney, and liver. In particular, nodules appeared and huge numbers of V. harveyi cells colonized the liver at 12 h postinfection (hpi) with highly virulent V. harveyi. Although no V. harveyi was detected in the gut, the infection simultaneously induced a gut-liver immune response. In particular, the expression of 8 genes associated with cellular immune processes, including genes encoding inflammatory cytokines and receptors, and pattern recognition proteins, was markedly induced by V. harveyi infection, especially with the highly virulent V. harveyi strain. V. harveyi infection also induced significant changes in gut bacterial community, in which Vibrio and Photobacterium increased but Bradyrhizobium, Lactobacillus, Blautia, and Faecalibaculum decreased in the group infected with the highly virulent strain, with accounting for 82.01% dissimilarity. Correspondingly, four bacterial functions related to bacterial pathogenesis were increased by infection with highly virulent V. harveyi, whereas functions involving metabolism and genetic information processing were reduced. These findings indicate that V. harveyi colonizes the liver and induces a gut-liver immune response that substantially disrupts the composition of and interspecies interactions in the bacterial community in fish gut, thereby altering the gut-microbiota-mediated functions and inducing fish death.

Vibrio harveyi 致使约 70% 的鲈鱼（Epinephelus sp.）患上弧菌病，严重限制了鲈鱼养殖业的发展。除了直接抑制病原体外，肠道微生物群在免疫稳态中发挥着至关重要的作用，并为宿主提供必要的健康益处。然而，关于对 V. harveyi 感染的免疫反应变化以及鲈鱼的肠道微生物群的资料仍然十分有限。为了揭示 V. harveyi 在珍珠鲹中的致病机制，我们研究了珍珠鲹在接触不同致病力的 V. harveyi 菌株后，病理变化、免疫反应以及肠道细菌群落的变异情况。在心脏、肾脏和肝脏中检测到明显的组织病理学变化。特别是，在感染高致病力 V. harveyi 12 小时后（hpi），肝内出现结节，并且大量的 V. harveyi 细胞定植。尽管在肠道中未检测到 V. harveyi，但感染同时诱导了肠道-肝脏免疫反应。特别是，V. harveyi 感染显著诱导了与细胞免疫过程相关的 8 个基因的表达，包括编码炎症细胞因子和受体的基因以及模式识别蛋白的基因，尤其是高致病力菌株。V. harveyi 感染还导致肠道细菌群落发生显著变化，在高致病力菌株感染的组别中，弧菌和光杆菌增多，而根瘤菌、乳杆菌、布劳提亚和粪肠球菌的数量减少，差异度达到 82.01%。相应地，感染高致病力 V. harveyi 导致与细菌致病性相关的四个细菌功能增加，而涉及代谢和遗传信息处理的细菌功能则减少。这些发现表明，V. harveyi 定植肝脏并诱导肠道-肝脏免疫反应，从而显著扰乱鱼肠道中细菌群落的组成和种间相互作用，进而改变肠道微生物群介导的功能，并导致鱼类死亡。