Massilia varians P2-4 Supplementation Enhances Immunity, Antioxidant Capability, Intestinal Microbiota Diversity, and Disease Resistance Against Pseudomonas aeruginosa Infection in Chinese Mitten Crab Eriocheir sinensis

Massilia varians has potential as a probiotic to inhibit bacterial pathogens in aquaculture, but very limited information is available regarding its use in Chinese mitten crab Eriocheir sinensis for enhancing host immunity, antioxidant ability and intestinal microbiota homeostasis. In this study, a 40-day feeding trial was conducted to evaluate the protective effects of dietary supplementation with M. varians P2-4 on nonspecific immune response, antioxidant status, intestinal microbiota and resistance against Pseudomonas aeruginosa infection in E. sinensis. Results demonstrated that dietary supplementation with M. varians P2-4 at 6.0 × 106 to 6.0 × 108 CFU/g diet significantly boosted nonspecific immunity and improved antioxidant capability of E. sinensis, mainly as evidenced by markedly increased activities of plasma lysozyme, plasma superoxide dismutase, hepatopancreatic superoxide dismutase and catalase. Furthermore, crabs fed M. varians P2-4-supplemented diets exhibited markedly improvements in intestinal microbiota composition and diversity, and showed substantially enhanced survival following P. aeruginosa challenge, with 7-day relative percentage survival ranging from 76.9% to 100.0%. To the best of our knowledge, this is the first study to reveal that M. varians P2-4 supplementation functions as a new biocontrol strategy in E. sinensis by effectively improving the non-specific immunity, antioxidant status and intestinal microbiota to mitigate P. aeruginosa infection.