Metabolomics analysis of eastern oysters ( <i>Crassostrea virginica</i> ) exposed to <i>Vibrio cholerae</i> toxin

<i>Vibrio cholerae (V. cholerae)</i> is a type of bacterium that causes cholera, a severe diarrheal disease globally affecting hundreds of people annually. However, the effect of the <i>V. cholerae</i> toxin on oyster metabolite signatures has not been well studied. In this study, nuclear magnetic resonance (NMR) based metabolomics was applied to investigate the metabolic level response of eastern oysters (<i>Crassostrea virginica</i>) to cholera toxin (CT), under low concentrations. Our study demonstrated that the decrease of branched-chain amino acids (BCAAs) in oysters was a response to CT exposure at low concentrations (10 ng/mL) in gill and mantle extracts. Metabolites such as leucine and isoleucine were significantly decreased in gills with toxin exposure at 10 ng/mL, and similar but weaker changes were also observed at 1 ng/mL, indicating an early response to CT. However, the trend reversed at 20 ng/mL, with acetate and propionate significantly increased over control (p < 0.07), which is a sign of antioxidant defenses that could help the recovery of the BCAAs. In the hemolymph study, acetate and propionate levels correlated strongly with those in the tissue extracts at 20 ng/mL, suggesting that hemolymph metabolites begin contributing to gill metabolic perturbations. More importantly, a principal component analysis (PCA) also revealed a partial separation between the control and the 20 ng/mL CT group, indicating potential major perturbations in hemolymph metabolites. This study provides evidence that metabolites in oyster tissues resulting from exposure to <i>Vibrio</i> toxin can serve as a new early warning system for predicting potential human pathogen risks in both environmental and seafood exposure.