Changes in gut microbiota and physiological functions of mud crab (Scylla paramamosain) in response to Vibrio parahaemolyticus infection

The mud crab (Scylla paramamosain) is a major aquaculture species in southeastern China. However, intensifying farming has led to disease outbreaks, with Vibrio parahaemolyticus (Vp) infections causing high mortality and economic losses. Although gut microbiota is important for host health, its response to artificial Vp challenge in mud crabs remains poorly understood. In this study, we investigated gut microbiota and physiological responses to Vp infection resistant (VPS) and susceptible (VPD) mud crab groups. 16S RNA sequencing presented significant changes in microbial diversity, composition, and functional structure after Vp infection. Firmicutes significantly increased in VPS, but decreased in VPD, while Bacteroidetes significantly reduced in VPD. Compared to VPS, the structure of the intestine and hepatopancreas in the VPD group exhibited severe intestinal and hepatopancreatic damage, and reduced short chain fatty acids (including propionic and butyric acids) and antioxidant and immune enzyme activity (including superoxide dismutase, catalase, alkaline phosphatase, acid phosphatase, and polyphenol oxidase). In addition, RT-qPCR results indicated a significant upregulation of immune-related genes (including GLT, tKtA, α-2M, Lamp, proPO, Rab5, Toll1, Toll2, CTL-B, ALF5, NF-κB, and TNF-α) in the VPD. Thus, we found that during Vp infection, mud crabs in the VPS could regulate gut microbiota and restore physiological functions to normal levels, protecting them from infestation. The results of this study enhance our understanding of Vp-induced gut microbiota dysbiosis and immune activation in mud crabs, providing actionable targets for developing disease-resistant aquaculture strategies based on microbial-immune synergy.