Effects of feed supplementation with Lactobacillus reuteri and Bacillus subtilis on the liver immunity in largemouth bass (Micropterus salmoides)

In the culture of largemouth bass (Micropterus salmoides), probiotics play an important role. Probiotics such as Lactobacillus reuteri and Bacillus subtilis can enhance the immune systems of fish like M. salmoides and help them prevent diseases. The largemouth bass in this experiment were fed a diet containing B. subtilis (BS, 107 CFU/g) and L. reuteri (LR, 107 CFU/g) for 35 days. Investigations were conducted into how the two probiotics affected the liver antioxidant capacity and liver immunity of M. salmoides. The findings revealed that both the BS and LR groups activated the Nrf2/keap1 signaling pathway, significantly increasing the expression of genes such as Nrf2, SOD1, SOD2, GST, and CAT. Moreover, the BS group notably augmented the levels of AKP, T-AOC, SOD, and CAT in the liver. Importantly, the key immune-related pathways enriched for differentially expressed genes in the BS group for hepatic transcriptional machinery encompassed complement and coagulation cascades, IL-17 signaling pathway, and chemokine signaling pathway. In conclusion, B. subtilis and L. reuteri demonstrate the ability to enhance the hepatic antioxidant capacity and immunocompetence of M. salmoides. However, significant differences exist in the intensity of their effects and the types of immune pathways activated in the liver. Both hold promising application value, and this study lays a foundational groundwork for the utilization of B. subtilis and L. reuteri in M. salmoides aquaculture.