Abstract:To understand the roles of antimicrobial peptides expressed in microalgae for aquaculture, expression vectors containing Cath-1a (from rainbow trout) gene were constructed and introduced to Nannochloropsis oceanica, N. limnetica and Phaeodactylum tricornutum, respectively. Randomly selected transformants were confirmed by PCR and Western Blot. Positive clones were used for the in vitro bacteriostatic experiments, and some lines were used as additives to feed zebrafish in order to test the effect of different nutrients on the immune system of fish. The results showed that all the three algal strains had successfully expressed exogenous antimicrobial peptides. Only P. tricornutum showed a bacteriostatic effect on Edwardsiella tarda, a common pathogenic bacterium in aquaculture, and there was no significant difference in the bacteriostatic effect between the wild-type and transformants of the three species of microalgae. The growth of zebrafish fed with algae as additives had no significant difference compared with the control (without additives). The expression levels of antioxidant and immune related genes together with the content of malondialdehyde (MDA) in the liver of zebrafish indicated that zebrafish fed with additives showed stronger antioxidant and anti-inflammatory ability than the control, and expression of antimicrobial peptides (PtC, a wild-type P. tricornutum strain Pt1 transformant expressing Cath-1a gene) could further enhance the immunity of zebrafish. In addition, the anti-inflammatory capacity of the group with Pt6 (a wild-type P. tricornutum strain with high fucoxanthin content) additives is more significant than that of the group with PtC additives, which indicated that fucoxanthin and eicosapentaenoic acid (EPA) in P. tricornutum might enhance disease resistance of zebrafish.