Identification and characterization polar tube protein 2 (PTP2) from Enterocytozoon hepatopenaei and its potential effect on shrimp microsporidian germination activity evaluation

Abstract

Microsporidia are obligate, intracellular, spore-forming parasites, whose hosts involve almost all animals from invertebrates to vertebrates. In the last decade, the microsporidium Enterocytozoon hepatopenaei (EHP) mainly infects the hepatopancreas of shrimp to hinder the host's growth, causing substantial economic losses in farms. Polar tube, as an important taxonomy index, is a unique highly specialized invasion apparatus of microsporidia. It is composed of polar tube proteins (PTPs), and more than six polar tube proteins have been identified from various microsporidia. In this study, we have successfully identified the polar tube protein 2 of EHP. EHPPTP2, rich in lysine, encoded 284 amino acids, and it contained a signal peptide of 15 amino acids at the N-terminus. The sequence alignment analysis revealed that EHPPTP2 was homologous with other polar tube protein 2 from microsporidia Ent. bieneusi, Encephalitozoon cuniculi, Enc. hellem, Enc. intestinalis and Enc. romaleae. Additionally, EHPPTP2 was expressed in mature EHP spores. Indirect immunofluorescence analysis (IFA) and immunoelectron microscopy (IEM) results showed that EHPPTP2 was localized on the whole polar tube of germinated spores. This is the first study to identify and characterize the polar tube protein from aquatic microsporidia, and these results could serve for the following epidemiological study and provide a reliable target for EHP diagnosis.