Beneficial effects of probiotics on Litopenaeus vannamei growth and immunity via the recruitment of gut Rhodobacteraceae symbionts

There is evidence that probiotics addition enriches the gut Rhodobacteraceae species that are key and beneficial symbionts in shrimp Litopenaeus vannamei fitness. Thus, it is of great significance to explore how the Rhodobacteraceae community implicates the assembly of shrimp gut microbiota for optimizing probiotics application. Here, we explored whether probiotics benefited shrimp health and fitness via the recruitment of gut Rhodobacteraceae commensals. Probiotics addition significantly improved feed conversion ratio, digestive and immune activities, thereby improving shrimp growth. Additionally, probiotics addition significantly altered gut microbial structures, enriched gut Rhodobacteraceae taxa, and reduced average variation degree, thereby stimulating a more stable gut bacterial community. The removal of Rhodobacteraceae nodes caused a faster decline in natural connectively of gut network than removal of non-Rhodobacteraceae nodes, reinforcing that Rhodobacteraceae species contributed disproportional roles in sustaining network stability. In accordance, probiotics addition promoted the migration of Rhodobacteraceae taxa from the aquatic environment to shrimp gut, although it increased deterministic selection governing the overall gut microbiota. Transcriptomic analysis showed that the induced expressions of amino acid metabolism and NF-κB signaling pathways were positively correlated with the gut Rhodobacteraceae population. Collectively, probiotics addition could enrich key gut Rhodobacteraceae commensals and potentiate gut network stability, as well as induction of host digestive and immune activities, thereby improving shrimp growth performance. Our study depicts a new perspective on the ecological and molecular mechanisms of probiotics beneficial effects on shrimp fitness.