Improved immune function of Chinese soft-shelled turtles (Pelodiscus sinensis) through oral probiotics via the TLR signaling pathway

In recent years, large-scale farming of Chinese soft-shelled turtles ( Pelodiscus sinensis ) has been developing rapidly. However, bacterial infections and environmental stresses limit its healthy development and probiotics have the potential to improve turtles' immunity and reduce disease occurrences. The objective of this study was to evaluate the effects of Bacillus subtilis B10 on intestinal health and immune function of Chinese soft-shelled turtles and explore its mechanism. The results showed that the dietary administration of B. subtilis B10 remarkably increased the levels of urea nitrogen and IL-1β, the activities of alkaline phosphatase, lactic dehydrogenase and antioxidant enzymes (including superoxide dismutase and catalase) in serum of Chinese soft-shelled turtles. Furthermore, B. subtilis B10 up-regulated the expression of genes related to intestinal tight junction protein and TLR8, which improved the intestinal health status and immune function of Chinese soft-shelled turtle. Finally, RNA-Seq results showed that TLR5 expression was significantly increased in liver. It could be concluded that probiotics B. subtilis B10 may improve the immune function of Chinese soft-shelled turtles via TLR5 in the liver. • Bacillus subtilis B10 could improve the antioxidant ability and immunity of serum of Chinese soft-shelled turtle. • B. subtilis B10 could improve the intestinal immunity of Chinese soft-shelled turtle by activating TLR8-MyD88-dependent signaling pathway. • Gut-derived flagellin could reach the liver and activate TLR5 through the intestinal barrier, thus improving the immunity of Chinese soft-shelled turtle.