Comparative transcriptomic analysis of gene expression profiles in the liver and spleen of American bullfrog (Lithobates catesbeianus) in response to Citrobacter freundii infection

In recent years, bullfrog (Lithobates catesbeianus) has become one of the most commercially important amphibians for aquaculture in China, and its annual production has grown rapidly. However, bacterial diseases caused by Citrobacter freundii infection have resulted in enormous economic losses. The present study used RNA sequencing technology to analyze the transcriptomic profile and differentially expressed genes (DEGs) in the bullfrog liver and spleen post C. freundii infection. De novo assembly resulted in the generation of 77,556 L. catesbeianus transcripts, and 49,421 of these genes were successfully annotated to the databases. Overall, 1487 DEGs were identified in the liver group, including 788 upregulated and 709 downregulated DEGs. A total of 799 DEGs, including 311 upregulated and 488 downregulated genes, were detected in the spleen groups. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed significantly enriched pathways, including pathways involved in metabolism and immune responses. The processes in which the DEGs were enriched were those related to metabolic activities, including the lipid metabolism pathway, amino acid pathway, immune-related pathway, and inflammatory responses. The results of this study provide insight into the response of bullfrogs against C. freundii at the transcriptome level and reveal the mechanism of the immune response against C. freundii.