Protection of Litopenaeus vannamei against the white spot syndrome virus using recombinant Pm-fortilin expressed in Pichia pastoris

Pm-fortilin/TCTP is a highly expressed protein in white spot syndrome virus (WSSV) infected shrimp, Penaeus monodon. It was demonstrated in insect cell line that Pm-fortilin could down regulate the expression of WSSV early genes and inhibit viral replication. To confirm this function in shrimp, dsRNA was designed to target endogenous fortilin. The dsRNA significantly reduced the expression of Pm-fortilin mRNA within 12 days after introducing them in P. monodon. The mortality rates after Pm-fortilin knockdown in WSSV-challenged P. monodon significantly increased compared with those of the controls. The silencing of Pm-fortilin also lowers the expression levels of prophenoloxidase (proPO) and fortilin binding protein (FBP1). This implies the interconnection of these three molecules in immune responsive pathways. To investigate the practical approach of Pm-fortilin in aquaculture, the sonicated yeast Pichia pastoris that harbored recombinant Pm-fortilin protein was added to the food that was ingested by another commercially important species, Litopenaeus vannamei. We revealed that protection against WSSV but not YHV can be conferred in L. vannamei. The reduced levels of WSSV in surviving animals that were fed a diet containing 5% yeast harboring recombinant Pm-fortilin was confirmed. The purified recombinant protein was stable at pH values ranging from 6-9, salinities of 15-30 ppt and temperatures of 50-90 °C. These results imply that the Pm-fortilin confers a specific clearance effect on WSSV and can act as a useful feed additive. Pm-fortilin and some WSSV proteins may be involved in the process of latency or prevention of WSSV replication.