Effects of dietary Bacillus velezensis LSG2-5 on digestion, intestinal morphology, microflora, and related gene expression in Rhynchocypris lagowskii Dybowski

Abstract

The study was to investigate at how Bacillus velezensis LSG2-5 from the host intestine affected the digestive function, intestinal morphology, intestinal microflora, and expression expression of tight junction protein genes in Rhynchocypris lagowskii Dybowski. Different doses of B. velezensis LSG2-5 were added to diets, namely control (0 CFU/g), B-6 (106 CFU/g), B-7 (107 CFU/g), B-8 (108 CFU/g) and B-9 (109 CFU/g) groups. Fish (mean weight: 9.98 ± 0.05 g) were fed for 56 days. The trypsin, lipase, amylase, γ-glutamyltransferase, Na+-K+-ATPase, and alkaline phosphatase activity in the liver and intestines of the treatment groups considerably increased in comparison to the control group (p<0.05), according to the results. Contrasted with the control group, the muscle layer thickness, lamina propria width, intestinal fold height, and fold breadth of the B-7, B-8, and B-9 groups increased considerably (p<0.05). Intestinal ZO-1, Claudin-3, and APN mRNA expression levels displayed significant up-regulation trends (p<0.05). The profusion of Proteobacteria, Bacteroidetes, Fusobacteria, and Cyanobacteria in intestines first increased and then decreased. In contrast, the abundance of Firmicutes showed an opposite trend. In summary, adding 107~109 CFU/g of B. velezensis LSG2-5 to feed can improve the intestinal health of R. lagowskii Dybowski.