Effects of high vp28 expression in Synechocystis sp. PCC6803 constructed by homologous recombination on immunity and antioxidant capacity of white spot syndrome virus infected Litopenaeus vannamei

This study represents the first instance of integrating the vp28 gene from the white spot syndrome virus (WSSV) into the genome of Synechocystis sp. PCC6803 using homologous recombination technology, resulting in the construction of the homologous recombinant algae strain Hrvp28-6803. Compared to the directly introduced plasmid transgenic cyanobacterium vp28-6803, the expression efficiency of vp28 in Hrvp28-6803 was found to be 2.87 times higher. Litopenaeus vannamei were orally immunized with the transgenic cyanobacteria and subsequently challenged with WSSV 7 days later. The cumulative survival rate of L. vannamei infected with WSSV was 56.66% after 10 days, reflecting a 13.33% increase compared to the vp28-6803 group. After the challenge, immune-related enzyme activities, including alkaline phosphatase (AKP) and acid phosphatase (ACP), as well as antioxidant-related enzyme activities of lactate dehydrogenase (LDH) and total antioxidant capacity (T-AOC), were measured in the hepatopancreas of the shrimp. The enzyme activities of AKP, ACP, and T-AOC in the Hrvp28-6803 group were significantly higher than those in the positive control group and the vp28-6803 group, while the LDH level was significantly lower than that in both the positive control group and the vp28-6803 group. The results demonstrate that the Hrvp28-6803 strain significantly enhances the survival rate of L. vannamei and enhances their immunity and antioxidant capacity. Therefore, the homologous recombinant Synechocystis Hrvp28-6803 can be utilized as an oral immunostimulant against WSSV to provide protection for L. vannamei.