The C-type lysozyme of Miichthys miiuy exhibits specific antibacterial activity against Gram-negative bacteria.

Abstract

Lysozyme is a key antimicrobial molecule in the innate immune system of fish, playing a central role in defending against pathogen invasion. In this study, a novel c-type lysozyme (mmi-LyzC) was identified and functionally characterized from Miichthys miiuy. The full-length cDNA was 432 bp, encoding a 143-amino-acid protein containing a conserved LYZ_C domain, in which the active sites Gluand Aspwere highly conserved across teleosts. After LPS challenge, the expression of mmi-LyzC in immune-related tissues was significantly upregulated, peaking at 48 h. The recombinant mmi-LyzC protein (rMmiLyzC) exhibited unexpectedly strong antimicrobial activity against two Gram-negative bacteria, while only moderate effect against a Gram-positive bacteria. The active protein was optimally produced by induction with 0.1 mM IPTG at 30 °C for 12 h, and it remained stable at pH 5-8. This study reveals the potent activity of mmi-LyzC against two Gram-negative bacteria and provides a potential target for improving bacterial disease resistance in aquaculture.