急性盐度胁迫对缢蛏肠道菌群结构及功能的影响

盐度是水产动物肠道微生物稳态的重要影响因子，其对水产动物的生长和健康有着重要影响。缢蛏（Sinonovacula constricta）是一种埋栖类的滩涂养殖贝类，常受到盐度波动的影响。然而，盐度是否对缢蛏肠道组织及其肠道菌群造成不利影响尚不清楚。为此，本研究设置了低盐（5）、正常盐度（20）和高盐（35）3个不同的盐度胁迫组，分别在胁迫前（正常盐度20，0 d）和胁迫15 d后收集缢蛏样品，利用组织病理学、16S rRNA高通量测序技术以及PICRUSt2工具对各处理组样品的肠道组织结构、菌群构成及其潜在功能进行比较分析。结果显示，15 d的急性盐度胁迫对缢蛏肠道组织造成了不同程度的损害，表现为细胞空泡、组织坏死和绒毛杂乱等。在所有组中共鉴定到712个细菌操作分类单元（OTUs），其中共有OTUs占细菌总数的6.2%。低盐和高盐胁迫下缢蛏肠道主要优势菌分别隶属于γ-变形菌纲（γ-Proteobacteria）和α-变形菌纲（α-Proteobacteria）。急性盐度胁迫改变了肠道细菌α-多样性，且在低盐组中物种丰富度最低。低盐和高盐胁迫下缢蛏肠道细菌群落结构均发生了显著改变（p < 0.002），同时伴随肠道菌群种间互作的降低。3种盐度胁迫下缢蛏肠道菌群组装的生态过程主要是确定性过程，而在低盐胁迫下其确定性过程有所降低。功能预测结果表明，急性盐度胁迫显著改变了缢蛏肠道菌群介导的营养物质和能量代谢等相关的功能通路丰度，而与免疫相关的功能通路丰度在高盐组中显著升高。本研究结果表明，急性盐度胁迫可引起缢蛏肠道发生病理损伤并伴随肠道菌群及其潜在功能的明显改变，这些改变可能影响缢蛏的健康。

Effects of acute salinity stress on the gut bacterial community structure and functional potentials of Sinonvacula constricta

Salinity is a crucial factor affecting the gut microbial homeostasis of aquatic animals, which has a significant impact on their growth and health. Sinonovacula constricta, a buried cultivated bivalve in mudflat, is frequently affected by salinity fluctuation. However, it remains unclear whether salinity has undesirable effects on the gut tissue and microbial community of S. constricta. To address these concerns, this study set up three different salinity stress groups: low salinity (5), normal salinity (20) and high salinity (35), with normal salinity 20 at 0 day as the control. Samples of S. constricta were collected before stress (i.e., normal salinity 20, 0 day) and after stress for 15 days, and were analyzed the differences in gut tissue structure, gut microbial compositions and potential functions via using the histopathology, 16S rRNA high-throughput sequencing technology and PICRUSt2. Simultaneously, the guts from S. constricta under normal salinity at 0 day were taken for comparative analysis. The results showed that the acute salinity stress for 15 days caused varying degrees of damage to the gut tissue structure of S. constricta, as observed by the cell vacuolation, tissue necrosis and villi clutter. A total of 712 bacterial OTUs were identified across all groups, among which the number of shared OTUs accounted for 6.2% of total OTUs. The dominant bacteria in the gut of S. constricta under low- and high- salinity stress belonged to γ-Proteobacteria and α-Proteobacteria, respectively. Acute salinity stress altered the α-diversity of gut bacterial community, with the lowest species richness under low salinity stress. The gut bacterial community structure of S. constricta changed significantly (p < 0.002) under both low- and high- salinity stress, accompanied by a decrease in the interspecific interactions of gut bacterial community. The ecological processes governing gut bacterial assembly of S. constricta was mainly deterministic under three salinity stresses, and this process decreased under the low salinity stress. Functional prediction results showed that acute salinity stress significantly varied the abundance of S. constricta gut bacterial-mediated nutrient and energy metabolism-related functional pathways, whereas the abundance of immune-related functional pathways significantly increased under high salinity stress. These findings suggest that acute salinity stress can cause pathological damage to the gut of S. constricta, accompanied by obvious change in gut bacterial communities and functional potentials, which could affect the health of S. constricta.