Mitochondrial dynamics and description of a novel Myxobolus species infecting Piaractus mesopotamicus in Brazil.

A new Myxobolus species was identified infecting the gill arch of Piaractus mesopotamicus from a fish farm in São Paulo State, Brazil, and is described based on morphological, molecular, and biological data. Mature myxospores of Myxobolus naldonensis n.sp. were round in frontal view, with a length of 9.0 ± 0.3 µm, a width of 5.9 ± 0.3 µm, and a thickness of 5.2 ± 0.1 µm in the lateral view. Its polar capsules were elongated and equal size, occupying more than half of the myxospore, measuring 4.4 ± 0.2 µm in length, 1.7 ± 0.1 µm in width, and the polar tubules had 5 - 7 coils. Ultrastructural analysis revealed that the plasmodial wall was composed of a single membrane and that the sporogenesis process was asynchronous, with early developmental stages of myxospores in the periphery of the plasmodia and mature myxospores in the central part. Numerous mitochondria and pinocytotic channels were observed in the ectoplasm. Confocal analysis showed labeling of the nuclei of the sporoplasm, as well as of the valves and polar capsules. In mature myxospores a volume mitochondrial could be detected, but no labeling indicative of mitochondrial activity was observed. Molecular analysis based on the amplification and sequencing of small subunit ribosomal DNA (SSU rDNA) resulted in a 1968 bp sequence. Phylogenetic analysis grouped Myxobolus naldonensis n. sp. as sister species of Myxobolus tambaquiensis, which infects Colossoma macropomum, a fish belonging to the family Serrasalmidae.