Identification of Galectin 9(CcGal-9) and its antibacterial function in Yellow River carp (Cyprinus carpio haematopterus)

Li Wang^1,2,3Yuanyuan Hu¹Xudong Li⁴Ziyan Zhang¹Nan Wang¹Limin Chao¹Chengfei Li¹Pei Gao⁵Jinyou Ma^1,2*Lei Wang^6*Xiaojing Xia^1,7*

• ¹Henan Institute of Science and Technology, Xinxiang, China
• ²Postdoctoral Research Base, Henan Institute of Science and Technology, Xinxiang, China
• ³Postdoctoral Research Station in Biological Sciences, Henan Normal University, Xinxiang, China
• ⁴Fishery Technology Extension Station of Henan Provincex, Zhengzhou, China
• ⁵Henan Fisheries Technology Extension Center, Zhengzhou, China
• ⁶College of Life Science, Henan Normal University, Xinxiang, China
• ⁷Ministry of Education Key Laboratory for Animal Pathogens and Biosafety, Zhengzhou, China

Galectin-9 is a β-galactoside-binding lectin that functions as a critical pattern recognition receptor (PRR) in the host immune system. It initiates immune defense responses by recognizing and binding to pathogen-associated molecular patterns (PAMPs) located on the surface of microorganisms. In this study, a novel galectin-9 cDNA, designated CcGal-9, was identified in Yellow River carp (Cyprinus carpio haematopterus). The full-length cDNA of CcGal-9 is 963 base pairs (bp) in length and encodes a protein comprising 320 amino acids (aa). The predicted CcGal-9 protein contains two distinct carbohydrate recognition domains (CRDs), characteristic of tandem-repeat type galectins. CcGal-9 mRNA was predominantly expressed in the spleen, testicle and head kidney, with relatively lower expression levels detected in the liver and intestine. Upon infection with Aeromonas hydrophila and Staphylococcus aureus, CcGal-9 expression was significantly upregulate in the liver, spleen, head kidney, kidney, gill and intestine. Recombinant CcGal-9 (rCcGal-9), purified from Escherichia coli BL21 (DE3), exhibited binding activity for lipopolysaccharides (LPS), peptidoglycans (PGN), mannan and various microorganisms, including both Gram-negative and Gram-positive bacteria. Moreover, rCcGal-9 demonstrated the ability to bind and agglutinate a broad spectrum of microorganisms. Furthermore, supplementation with varying concentrations of rCcGal-9 significantly improved the survival rate of Cyprinus carpio following infection with A. hydrophila. In summary, this study suggests that CcGal-9 plays a critical role in the immune defense of C. carpio against pathogenic microorganisms by functioning as an important PRR that recognizes PAMPs and agglutinates invading microbes.