C-type lectin response to bacterial infection and ammonia nitrogen stress in tiger shrimp (Penaeus monodon)

C-type lectins (CTLs) are pattern recognition receptors (PRRs) that are important in invertebrate innate immunity for the recognition and elimination of pathogens. Although they were reported in many shrimp, C-type lectins subfamily contain a large number of members with different functions that need to research in deep. In this present study, a new type of CTL, PmCL1 with 861 bp long full-length cDNA, that encodes a protein with 164-amino acid from a 495-bp open reading frame, was isolated and characterized from tiger shrimp (Penaeus monodon). The mRNA transcript of PmCL1 showed the highest expression in the hepatopancreas, whereas it was barely detected in the ovary. After the shrimp were stimulated by Vibrio harveyi and Vibrio anguillarum, PmCL1 expression in the hepatopancreas and gill was significantly upregulated. A carbohydrate-binding assay revealed the specificity of PmCL1 for pathogen-associated molecular patterns (PAMPs) that included peptidoglycan (PGN) and lipopolysaccharide (LPS), and saccharides that included d -glucose, galactosamine, α-lactose, treholose, and d -mannose. Recombinant PmCL1 agglutinated gram-positive (Staphylococcus aureus) and gram-negative bacteria (V. harveyi, V. anguillarum, Vibrio alginolyticus, Vibrio parahemolyticus, Vibrio vulnificus, and Aeromonas hydrophila) in the presence of calcium ions and enhanced the efficiency of clearing the invading bacteria. Collectively, our results suggested that PmCL1 might play an important role as a pattern recognition receptor (PRR) in the immune response towards pathogen infections, as well as the response towards ammonia nitrogen stress.