Integrated Vibrio load variation and transcriptome profiles provide new insights into the defensive response of Cyclina sinensis under Vibrio parahaemolyticus infection.

Vibrio parahaemolyticus is the dominant pathogen in mariculture, leading to the bivalves' mass summer mortality. This study investigated the antibacterial defense mechanism of the Cyclina sinensis against V. parahaemolyticus. The immersion challenge revealed that the daily mortality of C. sinensis increased and then decreased gradually, and the mass mortality occurred about a week after V. parahaemolyticus infection. The Vibrio load in the hepatopancreas of C. sinensis was dramatically increased at 12-24 hpi (hours post-infection) and then declined significantly at 2-7 dpi (days post-infection). RNA-Seq generated 866 differentially expressed genes (DEGs), and KEGG analyses enriched multiple innate immune-related and metabolic-related pathways. The expression levels of nine immune-related and metabolic-related DEGs were significantly changed after Vibrio infection, and their temporal expression patterns were multiple. Our results indicated that the immunity and metabolic responses might be reprogrammed to protect the host against pathogens at the early infection phase. This study would expand our knowledge of the pathogenesis mechanisms of clams infected with Vibrio and provide a theoretical basis for healthy shellfish cultivation.