Type II ice structuring protein (ISP II) gene and its potential role in low temperature tolerance in Manila clam, Ruditapes philippinarum

To elucidate the function of type II ice structuring protein (ISP II) in the cold tolerance and resistance of Ruditapes philippinarum, we investigated ISP II mRNA expression, the antifreeze effect of recombinant ISP II protein, and adaptation of R. philippinarum after acute and chronic cold stress. Bacterial freeze-thaw experiments showed that ISP II significantly increased the survival rate of Escherichia coli BL21 (DE3) under low temperature stress, suggesting that it had a potential antifreeze effect. Furthermore, rISP II protein injections significantly increased the survival rate of R. philippinarum compared with a PBS control group. In addition, succinate dehydrogenase (SDH), lactate dehydrogenase (LDH), and glutathione peroxidase (GSH-Px) activities, Malondialdehyde (MDA) content, total antioxidant capacity (T-AOC), and immune-related genes (Syk, SCD, and SOD) were measured in three populations of clams (northern, southern, and zebra). The results indicated that ISP II was likely to improve the cold resistance and performance of R. philippinarum under cold stress. These results not only provided molecular insights for improving the low-temperature resistance and immunity of shellfish but also provided useful information for improving the low temperature tolerance of R. philippinarum in aquaculture environments.