Morphological and genetical description of Loma psittaca sp. n. isolated from the Amazonian fish species Colomesus psittacus.

A previously unrecognised fish-infecting microsporidia (Loma psittaca n. sp.), found adherent to the intestinal mucosa of the freshwater puffer fish Colomesus psittacus (Teleostei, Tetraodontidae) from lower Amazon River, was described based on light and transmission electron microscope and phylogenetic analysis. The whitish xenoma was completely filled by numerous spores, including several developmental stages of the parasite. In all of these stages, the nuclei were monokaryotic. The merogonial plasmodium divided by binary fission and the sporont gave rise to disporoblastic ovoid spores measuring 4.2 +/- 0.4 x 2.8 +/- 0.4 microm. In mature spores, the polar filament was arranged in 10-11 (rarely 12) coils in one row in turn of posterior vacuole. The polaroplast had two distinct regions around the manubrium. The polyribosomes were organised in coiled tapes. The small subunit rRNA gene was sequenced and maximum parsimony analysis placed the microsporidian described here in the clade that includes the genera Ichthyosporidium, Loma and Pseudoloma. Based on differences from previously described microsporidians, such as ultrastructural characteristics of the xenoma, developmental stages including the spore and phylogenetic analysis supported the recognition of a new species, herein named L. psittaca n. sp.