Immune function of a novel lysozyme in Litopenaeus vannamei and its application as a feed supplement.

As a key component of humoral immunity within the innate immune system, lysozyme plays a crucial role in host defense against pathogenic infections. In this study, the cDNA sequence of an i-type lysozyme was obtained from Litopenaeus vannamei, and designated as LvLysi3. Following stimulation by Vibrio parahaemolyticus, transcripts of LvLysi3 in shrimp intestine, hepatopancreas and hemocytes was significantly up-regulated. Activity assays with recombinant protein showed LvLysi3 had agglutination activity and antibacterial activity against a broad spectrum of Gram-positive and Gram-negative bacteria. Furthermore, we found that LvLysi3 possessed high thermal stability and robust acid resistance, while also being non-toxic to human cells, ensuring the safety and potential application of this lysozyme as a feed additive. The incorporation of LvLysi3 into the feed could mitigate the detrimental effects of V. parahaemolyticus on L. vannamei by modulating reactive oxygen species (ROS) levels. Additionally, it promoted an increase in beneficial intestinal bacteria and reduced the abundance of V. parahaemolyticus. Moreover, feeding shrimp with LvLysi3 enhanced their innate immune response and facilitated pathogen phagocytosis by hemocytes, thereby decreasing the mortality rate associated with bacterial infections in shrimp. This study identifies an eco-friendly strategy to enhance shrimp health and control bacterial diseases of shrimp.