The plerocercoid of Spirometra mansoni can parasitize both human and animals, resulting in sparganosis. Lactate dehydrogenase (LDH) is an important enzyme in parasites. However, our knowledge of the LDH family in S. mansoni is still inadequate. This work identified 19 new LDH members in S. mansoni. Clustering analysis demonstrated that all SmLDHs were divided into two main groups, which is consistent with the patterns of conserved motif organization. According to RT-qPCR, 2 LDHs were highly expressed in the plerocercoid stage and 17 LDHs were highly expressed in the adult stage. The evolutionary tree showed a high level of diversity of both cestode and trematode LDHs. SmLDHs contained both conserved family members and members in the process of further diversification. rSmLDH has a NAD-binding domain and a substrate-binding domain. The protein was immunolocalized in the epidermis of the pleroceroid and in the tegument, uterus and egg shell of adult worms. The optimum activity for rSmLDH in the pyruvate reduction reaction was found to be pH 4.5 and 37 °C. In the oxidation reaction, optimal values for pH and temperature were 9.0 and 30 °C, respectively. Gossypol was found to be the most powerful inhibitor in both reduction and oxidation reactions. The results provide a basis for the further study of the biological roles of LDHs in S. mansoni and other LDH-containing taxa.
Keywords: cestode; enzymatic traits; identification; lactate dehydrogenase; phylogeny.