Lactobacillus plantarum E2 regulates intestinal microbiota and alleviates Pseudomonas plecoglossicida induced inflammation and apoptosis in zebrafish (Danio rerio)

Pseudomonas plecoglossicida infection is a highly contagious epidemic in aquaculture, causing significant mortality among teleost. Our previous research has demonstrated that Lactobacillus plantarum E2 is beneficial for large yellow croaker in resisting infections caused by P. plecoglossicida. However, the relevant mechanisms remain largely unclear. In the present study, we used zebrafish (Danio rerio) to further explore the function of L. plantarum E2 and its mechanisms for resisting P. plecoglossicida infection. E2 supplementation diet significantly improved the growth rates and α-amylase and trypsin activities of the liver in zebrafish. After challenge with P. plecoglossicida strain PQLYC4, the survival rates of zebrafish were improved, and immune-related genes expression (IL-1β, TNF-α, IL-8, Ig-Z, TLR-22 and IL-12α) were down-regulated. Histological analysis showed that E2 group had a longer intestinal villus and thicker intestinal walls after 30 days of feeding and healthier intestinal structure after challenge with P. plecoglossicida strain PQLYC4. Furthermore, co-incubation of zebrafish embryo fibroblast (ZF-4 cells) with L. plantarum E2 reduced apoptosis of ZF-4 cells after exposed to P. plecoglossicida. Intestinal microbiota analysis showed that E2 strain significantly increased the relative abundance of Lactobacillus and Pseudomonas, and PCoA analysis revealed a noticeable divergence in the intestinal microbial communities after E2 supplement. Together, our results suggested that E2 strain may promote zebrafish survival against P. plecoglossicida infection by regulating the intestinal microbiota and alleviating inflammatory response and apoptosis, thus exhibiting the potential as a probiotic.