Morphology, proteome and metabolome characterization of the sporoplasm of Ameson portunus (Microsporidia)

Infective sporoplasms are the first stage of intracellular survival and propagation for Microsporidia, yet there is a paucity of knowledge regarding their biological characteristics. In this study, we successfully germinated Ameson portunus in vitro, and for the first time, we successfully isolated and purified the sporoplasm of this aquatic microsporidian. Morphological observations show that sporoplasms are spherical, non-refractive, and are similar in size to mature spores. Further ultrastructural observations show that sporoplasms are enclosed by a single membrane, with a single nucleus, their cytoplasm covering a monokaryotic nucleus is relatively granular and homogeneous. Comparative proteomic and metabolomic analyses of sporoplasms and mature spores suggest that 214 significantly differentially expressed proteins (DEPs) and 198 significantly differentially expressed metabolites (DEMs) are possibly involved in the spore germination processes. Several DEPs involved in glycolysis, the pentose phosphate pathway, aminoacyl-tRNA synthesis, nucleotide metabolism and ribosome pathways were upregulated in sporoplasms. Specially, the expression of several transporter proteins was also significantly increased in sporoplasms. Correspondingly, some DEMs involved in aminoacyl-tRNA synthesis, nucleotide metabolism, and amino acid biosynthesis pathways were downregulated. Collectively, our results indicate that significant metabolic activities, including energy and nucletotide and protein synthesis have been initiated in the in vitro produced sporoplasms of A. portunus to prepare for the transition of the parasites from the dormant stage to the active infective stage.