Chicken-type lysozyme functions in the antibacterial immunity in red swamp crayfish, Procambarus clarkii

Lysozymes possess antibacterial activities, making them crucial defense proteins in innate immunity. In this study, a chicken-type (c-type) lysozyme (designated PcLyzc) was cloned and characterized from red swamp crayfish Procambarus clarkii. The full-length cDNA had an open reading frame of 435 base pairs encoding a polypeptide of 144 amino acid residues. Multiple alignments and phylogenetic analysis revealed that PcLyzc shared high similarity to the other known invertebrate c-type lysozymes. PcLyzc transcripts were steadily expressed in a wide range of tissues in healthy crayfish, and were prominently up-regulated in the hepatopancreas and gills after Vibrio anguillarum or Aeromonas hydrophila challenge. Recombinant PcLyzc showed inhibitory activity in vitro against both Gram-positive bacteria, including Staphylococcus aureus, Micrococcus luteus and Bacillus thuringiensis, and Gram-negative bacteria, including A. hydrophila, V. anguillarum and Escherichia coli. By overexpressing PcLyzc through introducing exogenous recombinant protein, or silencing PcLyzc expression through injecting double strand RNA, it was found that PcLyzc could help eliminate the invading bacteria in crayfish hemolymph and could protect crayfish from death, possibly by promoting the hemocytic phagocytosis. These results indicated that PcLyzc played a role in the antibacterial immunity of crustaceans, and laid a foundation of developing new therapeutic agents in aquaculture.