Pathogenicity and immune response of the sea urchin Mesocentrotus nudus to Vibrio coralliilyticus infection

Abstract

Bacterial infectious diseases, as one of the serious threats to sea urchins, have brought great economic losses to the farming industry in East Asia. In the present work, we isolated a pathogen named Vibrio coralliilyticus G2–37 from the sea urchin Strongylocentrotus intermedius with overt disease symptoms. Here, we first confirmed this bacterium as a potential pathogen of the sea urchin Mesocentrotus nudus and then assessed its impacts on the survival, histology, and immune responses of M. nudus. The median lethal dose (LD50) for G2–37 on M. nudus was determined to be 4.486 × 105 CFU/mL by a bacterial challenge experiment. Histopathological examination showed that V. coralliilyticus caused severe damage to the intestine, gonad, and perioral membrane of M. nudus in the late stage of infection. Flow cytometry demonstrated that V. coralliilyticus could significantly induce the apoptosis of M. nudus coelomocytes. Moreover, we found that M. nudus presented complex tissue-specificity and time-dependent immune responses after V. coralliilyticus infection. Principal Component Analysis (PCA) revealed that the physiological states of the intestine, coelomocyte lysate supernatant (CLS), and cell-free coelomic fluid (CCF) from M. nudus were strongly affected with increasing duration of infection. Integrated biomarker response (IBR) analysis proved that V. coralliilyticus infection could decrease the immune capacity and increase the oxidative damage of M. nudus, leading to potential consequences for sea urchin health. M. nudus might exist for a certain steady period at 60 h after pathogen infection, but they still face a survival crisis under the long-term challenge of the pathogen.