Immune response and intestinal microbial succession of half-smooth tongue sole (Cynoglossus semilaevis) infected with Vibrio vulnificus

This study aimed to investigate the responses of the immune system and intestinal microbiota of half-smooth tongue sole (Cynoglossus semilaevis) to Vibrio vulnificus infection. The innate immune indicators in peripheral blood and liver were measured, and the process of microbial succession monitored. Half-smooth tongue sole (length: 29.75 +/- 2.63 cm, bodyweight: 116.21 +/- 7.34 g) were selected to perform the pathogen challenge test. The control group (C) was intraperitoneally injected with 100 mu L PBS. The inoculation amount of Vibrio vulnificus for the low-dose group (L), moderate-dose group (M), and high-dose group (H) were 1 x 10(4), 1 x 10(7), 1 x 10(10) cells for each fish, respectively. A decrease and an increase in the proportions of lymphocytes and monocytes, respectively, was observed at 24 h of L, M and H. Within initial 72 h, the joint action of monocytes, neutrophils, and eosinophils to cope with the pathogen infection only occurred in H. The serum CH50 and ALP levels were significantly higher and serum lysozyme activity significantly lower in H than those observed in C at 48 h (P < 0.05). Moreover, within the initial 72 h, lysozyme activity of the liver was significantly lower (P < 0.05) in H. The intestinal microbiota shifted significantly within the initial 24 h in H and 48 h in M. The bacteria: Shewanella, Pseudoalteromonas, Acidobacteria, Firmicutes, and Actinobacteria, showed some resistance to Vibrio to a certain range. From our findings, the innate immunity in half-smooth tongue sole is not sensitive to moderate- or lowdose V. vulnificus infection. Leukocytes, ALP, and complement are primarily involved in resisting high-dose infection of V. vulnificus. A variety of intestinal microbial taxa plays a vital role in inhibiting V. vulnificus growth. In addition to bacteria from Firmicutes and Actinobacteria, bacteria from Acidobacteria are also a good probiotic option for resisting V. vulnificus.

Automated summary

The study found that the immune system of the half-smooth tongue sole is not sensitive to moderate- or low-dose Vibrio vulnificus infection, while leukocytes, ALP, and complement primarily play a role in resisting high-dose infection. A variety of intestinal microbial taxa are important in inhibiting Vibrio vulnificus growth.