Abstract
The intestinal microbiota plays a vital role in host health and environmental adaptation. However, the response of the gut microbial community in Penaeus vannamei to hypersaline conditions remains poorly understood. In this study, we used metagenomic sequencing to compare the structural and functional profiles of intestinal bacteria in shrimp reared in the L-, M- and H-salinity groups. Alpha-diversity increased significantly with salinity, and PCoA revealed clear separation of microbial communities among groups. Core species analysis showed that five of the seven shared core taxa belonged to Vibrio. Microbial source tracking indicated that the proportion of environmentally derived bacteria increased with salinity. Co-occurrence networks under M and H salinities were more complex but maintained stability comparable to L. Notably, the low-salinity group was enriched with potential pathogens (e.g., Vibrio, Chryseobacterium) and infection-related functions. Functional analysis revealed that the high-salt H group exhibited enrichment of enzymes such as proline dehydrogenase (PutB), glutamate-cysteine ligase (GshA), and methyltransferases (HpnR). These enzymes interconnect compatible solutes including L-proline, L-glutamate, betaine, dimethylglycine, and glutathione, playing a crucial role in enhancing microbial osmoprotection. Furthermore, shared functions across salinities were associated with energy metabolism, protein synthesis, osmoprotection, and antioxidation. These findings, for the first time, simultaneously reveal the potential pathogenic characteristics of the L-salinity group and the adaptation mechanisms of the H-salinity group to hypersaline environments from both structural and functional perspectives of shrimp intestinal microbiota, providing insights for health management in high-salinity aquaculture.