Transcriptional analysis combined with intestinal microbiota sequencing to unveil the effects of astaxanthin from Haematococcus pluvialis on pearl gentian grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus ♂)

Astaxanthin (ASX) shows strong antioxidant property and is widely used as a fish feed additive. However, the underlying molecular mechanism of how ASX improves the ability of fish to resist bacterial infection remains largely unknown. To investigate the effects of dietary ASX from Haematococcus pluvialis on pearl gentian grouper, transcriptome combined with intestinal microbe analysis was conducted. The results of RNA-Seq analysis demonstrated that compared with the control group, the differently expressed genes of ASX-treated group were enriched in AMPK, autophagy, HIF-1, and PI3K-Akt signaling pathway. 16 s rDNA of intestinal microbiota analysis revealed that the dominant bacteria in the intestine of fish fed with ASX were Proteobacteria and Bacteroidetes. Moreover, ASX-fed significantly reduced the level of reactive oxygen species (ROS) and NF-κb mRNA expression in fish with bacterial infection. ASX treatment also prolonged the survival time of fish in the infection condition. Our work reveals that ASX systematically improves the antibacterial ability of grouper by regulating AMPK, autophagy, HIF-1, and PI3K-Akt signaling pathway and assisting in the colonization of intestinal dominant flora.