Cloning and characterization of chst11 from Procambarus clarkii involved in the host immune response of white spot syndrome virus and Aeromonas hydrophila

Genomics and transcriptomics reveal new molecular mechanism of vibriosis resistance in fish

Infectious diseases have caused dramatic production decline and economic loss for fish aquaculture. However, the poor understanding of fish disease resistance severely hampered disease prevention. Chinese tongue sole (Cynoglossus semilaevis) is an important economic flatfish suffering from vibriosis. Here we used genomic, transcriptomic and experimental approaches to investigate the molecular genetic mechanisms underlying fish vibriosis resistance. A genome-wide comparison revealed that the genes under selective sweeps were enriched for glycosaminoglycan (GAG) chondroitin sulfate (CS)/dermatan sulfate (DS) metabolism. Transcriptomic analyses prioritized synergic gene expression patterns in this pathway, which may lead to an increased CS/DS content in the resistant family. Further experimental evidence showed that carbohydrate sulfotransferases 12 (Chst12), a key enzyme for CS/DS biosynthesis, has a direct antibacterial activity. To the best of our knowledge, this is the first report that the chst12 gene has a bactericidal effect. In addition, CS/DS is a major component of the extracellular matrix (ECM) and the selection signatures and fine-tuned gene expressions of ECM-receptor interaction genes indicated a modification in the ECM structure with an enhancement of the barrier function. Furthermore, functional studies conducted on Col6a2, encoding a collagen gene which constitutes the ECM, pointed to that it may act as a cellular receptor for Vibrio pathogens, thus plays an important role for the Vibrio invasion. Taken together, these findings provide new insights into the molecular protective mechanism underlying vibriosis resistance in fish, which offers crucial genomic resources for the resistant germplasm breeding and infectious disease control in fish culturing.

Pathogenicity of Aeromonas hydrophila causing mass mortalities of Procambarus clarkia and its induced host immune response

Outbreaks of mass mortalities among cultured Procambarus clarkia occurred in a commercial hatchery during the spring of 2019 in Jiangsu province of China. Here, we exploit the pathogenicity and immune response of Aeromonas hydrophila (GPC1-2), which was isolated from diseased P. clarkia. Crayfish challenged showed similar pathological signs to the naturally diseased P. clarkia, lethal dose 50% (LD₅₀) of the strain GPC1-2 to P. clarkia was 3.8 × 10⁶ CFU/mL. Detection of virulence-associated genes by PCR indicated that the strain GPC1-2 carried hlyA, aerA, alt, ast, act, aha, ahp, ahpA, and ahpB. Histopathological analysis of hepatopancreas revealed that the hepatic tubule lumen and the gap between the hepatic tubules became larger, and the brush border disappeared in the P. clarkia infected by GPC1-2. Quantitive real-time PCR (qRT-PCR) was undertaken to measure mRNA expression levels for six immune-related genes in P. clarkia after A. hydrophila infection. The expression level of proPO, NOS, ALF1, TLR2, PX, and AST were detected in hemolymph, hepatopancreas, gill and intestine tissues, and clear transcriptional activation of these genes were observed in the infected individuals. These results revealed pathogenicity of A. hydrophila and its activation of host immune response, which will provide a scientific reference for the breeding and disease prevention in P. clarkia culture.