Catalase eliminates reactive oxygen species and influences the intestinal microbiota of shrimp

• A novel catalase (CAT) involved in ROS elimination was identified in kuruma shrimp.
• MjCAT was upregulated in shrimp challenged by pathogenic bacteria via oral injection.
• ROS was accumulated and bacterial clearance increased in the MjCAT-RNAi shrimp.
• The intestinal epithelium was impaired and survival rate declined after MjCAT-knockdown.
• MjCAT participated in the intestinal host–microbe homeostasis by regulating ROS level.

Intestinal innate immune response is an important defense mechanism of animals and humans against external pathogens. The mechanism of microbiota homeostasis in host intestines has been well studied in mammals and Drosophila. The reactive oxygen species (ROS) and antimicrobial peptides have been reported to play important roles in homeostasis. However, how to maintain the microbiota homeostasis in crustacean intestine needs to be elucidated. In this study, we identified a novel catalase (MjCAT) involved in ROS elimination in kuruma shrimp, Marsupenaeus japonicus. MjCAT mRNA was widely distributed in hemocytes, heart, hepatopancreas, gills, stomach, and intestine. After the shrimp were challenged with pathogenic bacteria via oral infection, the expression level of MjCAT was upregulated, and the enzyme activity was increased in the intestine. ROS level was also increased in the intestine at early time after oral infection and recovered rapidly. When MjCAT was knocked down by RNA interference (RNAi), high ROS level maintained longer time, and the number of bacteria number was declined in the shrimp intestinal lumen than those in the control group, but the survival rate of the MjCAT-RNAi shrimp was declined. Further study demonstrated that the intestinal villi protruded from epithelial lining of the intestinal wall were damaged by the high ROS level in MjCAT-knockdown shrimp. These results suggested that MjCAT participated in the intestinal host–microbe homeostasis by regulating ROS level.