Transcriptomic analysis reveals the immunomodulatory role of Clostridium autoethanogenum protein on Litopenaeus vannamei under variable salinity conditions

Salinity is a critical environmental factor in aquaculture, and <i>Clostridium autoethanogenum</i> protein (CAP) shows potential as a new feed protein source. This 8-week study compared two diets (fish meal [FM] and CAP) for juvenile Pacific white shrimp (<i>Litopenaeus vannamei</i>) at salinity levels of 15‰, 30‰, and 45‰. A total of 720 <i>L. vannamei</i> with an initial average body weight of 0.38 ± 0.01 g were randomly assigned to six experimental groups, each with three biological replicates of 40 shrimp per replicate. The study examined CAP's impact on shrimp growth, immune response, and transcriptome, using two-way ANOVA to analyze the results. The results indicated that compared to the FM group, the shrimp in the CAP group exhibited a significantly higher weight gain rate and specific growth rate at the same salinity (<i>P</i> < 0.05). However, at 45‰ salinity, the shrimp in the CAP group had a higher feed conversion ratio and feed intake compared to the FM group (<i>P</i> < 0.05). After infection with white spot syndrome virus, the CAP group exhibited a significantly higher survival rate at 15‰ and 45‰ salinity compared to the FM group (<i>P</i> < 0.05). As salinity increased, most immune enzyme activities and gene expression levels in the FM group initially increased and then decreased (<i>P</i> < 0.05). Under the same salinity, except for phenoloxidase activity which showed no significant difference at 45‰ salinity, all other immune-related indicators and gene expressions in the CAP group were significantly higher than those in the FM group (<i>P</i> < 0.05). Transcriptome analysis revealed that the differentially expressed genes (DEGs) between FM and CAP groups at various salinity levels were primarily associated with immune and metabolic pathways. Additionally, by combining the analysis of these DEGs with immune-related indicators, it was observed that under different salinity conditions, CAP was associated with the co-expression of immune and metabolism-related genes as well as changes in enzyme activity. In summary, CAP as the main protein source boosts growth, disease resistance, and nonspecific immunity in <i>L. vannamei</i>, while also regulating immune enzyme activity and gene expression to improve adaptability to salinity changes.