Effect of trans-vp28 gene Synechocystis sp. PCC6803 on growth and immunity of Litopenaeus vannamei and defense against white spot syndrome virus (WSSV)

This study was aimed to assess the effect of oral administration of trans-vp28 gene Synechocystis sp. PCC6803 against white spot syndrome virus (WSSV) on the juveniles of Litopenaeus vannamei. Shrimp were immunized with trans-vp28 gene Synechocystis sp. PCC6803 for 10 days, followed by challenge with WSSV. The survival rate of each group of L. vannamei was then determined. We also detected the activities of phenoloxidase (PO), superoxide dismutase (SOD), catalase (CAT) and lysozyme (LYZ) in muscle and hepatopancreas at different time after immunization and after viral challenge. On the 7th day after challenge, the relative survival rate (RPS) of the experimental group (challenge, feeding mutant of Synechocystis sp. cells) was 88.42%, which was 3.47 times higher than that of the wild type group (challenge, feeding wild type of Synechocystis sp. cells), while all of the positive control group (challenge and no vaccination) died. Ten days after infection, the survival rate of experimental group was still as high as 62.5%, but the survival rate of wild type group was only 4.83%. There was no death in negative control group (neither vaccination nor challenge). The results showed that oral administration of trans-vp28 gene Synechocystis sp. PCC6803 could significantly enhance the ability of shrimp to resist WSSV. The analysis of immunological parameters after immunization showed that the activities of PO, SOD, CAT and LYZ in muscle and hepatopancreas in the experimental group were the highest, followed by the wild type group, control groups (positive and negative control group). The analysis of immunological parameters post challenge showed that the activities of the four enzymes in both tissues in the experimental group were higher than those in the wild type group and the positive control group, but the final enzyme activities of these three groups were lower than the negative control group. These results indicated that oral administration of trans-vp28 gene Synechocystis sp. PCC6803 could increase the activity of immune enzymes and enhance the defense ability of juvenile shrimp against WSSV infection.