Expression Profiles of Zebrafish (Danio rerio) Lysozymes and Preparation of c-Type Lysozyme with High Bacteriolytic Activity against Vibrio vulnificus

Lysozyme is a crucial component of the host’s innate immune system. Due to its natural non-toxic and harmless characteristics, lysozyme is considered to be an ideal antibiotic substitute. In this study, we analyzed the expression profiles of lysozymes from zebrafish (Danio rerio) in uninfected or V. vulnificus-infected tissues using real-time quantitative PCR (qPCR). Furthermore, lysozymes that might be involved in the defense against V. vulnificus were selected for over-expression, and the antibacterial activity of over-expressed lysozyme proteins were evaluated using V. vulnificus. The results showed that three types of zebrafish lysozyme, i.e., c-type lysozyme (DrLysC), g1-type lysozyme (DrLysG1), and g2-type lysozyme (DrLysG2), were identified, and V. vulnificus infection significantly changed the expression levels of DrLysC and DrLysG1. Then, DrLysC and DrLysG1 were over-expressed in E. coli, and the purified recombinant DrLysC (rDrLysC) showed more potent antibacterial activity against V. vulnificus. This finding lays the foundation for further application of rDrLysC to treat V. vulnificus infection.