低氧胁迫对脊尾白虾组织结构及肠道菌群的影响

Effects of hypoxic stress on tissue structure and gut bacterial community of Exopalaemon carinicauda

中文关键词: 脊尾白虾  低氧胁迫  组织结构  肠道菌群

英文关键词: Exopalaemon carinicauda  Hypoxic stress  Tissue structure  Gut bacterial community

中文摘要:

      为探究低氧胁迫对脊尾白虾(Exopalaemon carinicauda)组织结构及肠道菌群的影响，将脊尾白虾暴露于(2.5±0.2) mg/L低氧环境中24 h，常氧组溶解氧浓度为(7.2±0.2) mg/L，分别采集低氧组及常氧组样品的鳃、肝胰腺和肠道组织，对鳃和肝胰腺组织进行切片显微观察，并利用16S rRNA 基因测序技术分析低氧胁迫前后肠道菌群的变化。结果显示，低氧胁迫对鳃和肝胰腺组织结构均造成不同程度的损伤，低氧组和常氧组脊尾白虾的肠道菌群差异较大，变形菌门(Proteobacteria)、厚壁菌门(Firmicutes)在常氧组脊尾白虾肠道中占绝对优势，低氧组虾肠道中拟杆菌门(Bacteroidota)和放线菌门(Actinobacteriota)的数量显著升高(P<0.05)，变形菌门数量显著降低(P<0.05)。在科水平上，普氏菌科(Prevotellaceae)和毛螺菌科(Lachnospiraceae)在低氧组虾肠道中的数量显著高于常氧组(P<0.05)，而红杆菌科(Rhodobacteraceae)和假单胞菌科(Pseudomonadaceae)细菌在低氧组显著降低(P<0.05)。此外，部分潜在病原菌的数量在低氧组中显著升高(P<0.05)。研究表明，低氧胁迫显著改变了脊尾白虾肠道菌群结构，导致部分有益菌的数量显著降低，增加了弧菌病及肠道炎症性疾病的发病几率，并对鳃、肝胰腺组织造成不同程度的损伤。研究结果有助于阐释脊尾白虾对低氧环境的响应机制，为脊尾白虾健康养殖提供参考。

英文摘要:

      Exopalaemon carinicauda has the highest production in the Yellow Sea and Bohai Sea of China. Compared with those of other shrimp species, E. carinicauda has a short reproductive cycle, fast growth, and adaptability. The pond mono-culture and mixed culture mode is more common in small economic shrimp and can be used as an excellent biological material for crustacean biology research. Dissolved oxygen, an important environmental factor for aquatic animal survival, affects the growth, behavior, reproduction, immunity, and metabolism of aquatic animals and is highly susceptible to hypoxia due to high temperatures, flushing, water pollution, the expansion of the scale of aquaculture, high-density aquaculture, high temperatures, and climate change. Recently, studies have been conducted on the effects of hypoxia on aquatic animals, mainly focusing on immune response, energy consumption, respiration, and antioxidant character. Gill and hepatopancreas tissue are major organs in crustaceans and increasing evidence reveal that gut bacterial community are involved in host immune defense, nutrient absorption, and antioxidant processes. Therefore, investigating the effects of hypoxic stress on the tissue structure and gut bacterial community of E. carinicauda will help to elucidate the mechanism of the response of E. carinicauda to hypoxic environments, which will be useful for its healthy aquaculture. In this study, we collected gill, hepatopancreas, and gut tissues from experimental and control groups after 24 h of hypoxic stress (2.5±0.2) mg/L. The gills and hepatopancreas were sectioned and observed and the changes in gut bacterial community before and after hypoxic stress were analyzed using 16S rRNA gene sequencing. The experimental results showed that gill and hepatopancreas tissues underwent different degrees of damage after hypoxic stress; the gut bacterial community changed, some pillar and epithelial cells of gill tissues were disordered, the number of chloride cells was significantly reduced, chloride cells were changed from irregularly flattened to rounded, the secondary lamellae was aggravated, and the gill tissues changed their morphology and structure to alleviate the hypoxic stress. The number of storage cells in hepatopancreas tissues did not change significantly compared with that of the control group, the lumen contracted significantly, the morphology and structure of the entire hepatic tubule contracted, the volume of transport vacuole increased significantly and even ruptured, and the number of secretory cells decreased significantly. Although shrimp gut bacteria are numerous and diverse the vast majority of gut bacteria are reported to be concentrated in a few dominant bacterial phyla, such as Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes. The richness and diversity of gut bacterial community of individuals in the experimental group changed significantly after hypoxic stress and Proteobacteria and Firmicutes were the dominant bacterial phylum in the guts of the control group, accounting for 81.42% and 11.18% of the total amount, respectively. The amounts of Bacteroidota and Actinobacteriota were significantly higher (P<0.05), and that of Proteobacteria were significantly lower (P<0.05) in the experimental group. At the family level, the numbers of Prevotellaceae and Lachnospiraceae were significantly higher (P<0.05) in the experimental group than those in the control group. Rhodobacteraceae bacteria had a relative high abundance in the gut of healthy E. carinicauda and their amounts were significantly reduced after hypoxic stress. In addition, the numbers of some potential pathogenic bacteria were significantly higher (P<0.05) in the experimental group. At present, multiple studies are being conducted on aquatic animals under hypoxic stress; however, the effects of hypoxic stress on the tissue structure and intestinal flora of E. carinicauda remains unexplored. In this study, we observed the damage of tissue structure and simultaneously analyzed the changes in intestinal flora of E. carinicauda under hypoxic stress, to deeply study the physiological response to stress under hypoxic conditions of E. carinicauda and provide basic scientific research on the actual production and cultivation of a novel species of E. carinicauda that is resistant to hypoxic conditions. This will provide basic scientific research information for the actual production and cultivation of novel hypoxia-tolerant varieties of E. carinicauda.