Comparative Analysis of Immunostimulatory Effects of Various Synechococcus elongatus-Based CpG ODN Constructs on Litopenaeus vannamei

CpG ODNs have been confirmed to exhibit immunostimulatory effects on *Litopenaeus vannamei*. Currently, tandem CpG ODNs produced using *Escherichia coli* as the engineering bacterium are commonly applied in shrimp. However, due to the unique structure of CpG ODNs, it is difficult to randomly concatenate them, and there is a risk of endotoxin contamination during extraction. In this study, *Synechococcus elongatus* was used as a carrier to construct eight types of CpG ODNs, and their immunostimulatory effects, growth-promoting roles, and regulatory impacts on intestinal microbiota were compared.