Differential gene expression profiles in Japanese flounder (Paralichthys olivaceus) with different susceptibilities to edwardsiellosis

Edwardsiellosis, which is caused by Edwardsiella tarda, a Gram-negative bacterium, is one of the most serious problems in Japanese flounder (Paralichthys olivaceus) culture. In this study, we examined the immune responses at the molecular level of genetic groups of Japanese flounder that are either susceptible or moderately susceptible to E. tarda infection using a cDNA microarray which was spotted with approximately 2000 different genes. Four different genetic groups of Japanese flounder (groups A, B, C and D) were infected with E. tarda by immersion. Mortality was 100% in groups A and C but only about 50% in groups B and D. Microarray analyses revealed 36 genes that were differentially expressed between the susceptible (A and C) and resistant (B and D) groups before E. tarda infection. Three days after the challenge, the resistant groups highly expressed MHC class I antigen processing and presentation–related genes, while the susceptible groups highly expressed genes involved in innate immune responses. The microarray results could be useful for selective breeding to enhance disease resistance of Japanese flounder against E. tarda and for studying strategies for controlling edwardsiellosis.