Chromosomal localisation of five genes in Perkinsus olseni (Phylum Perkinsozoa).

The molecular karyotype of Perkinsus olseni, a pathogenic protist that infects the clam Ruditapes decussatus, comprises nine chromosomes, ranging in size from 0.15 Mb to 6.5 Mb, representing a haploid genome of about 28 Mb. In order to establish chromosome specific markers, PCR-amplified DNA sequences belonging to five conserved genes (18S rRNA, actin type I, hsp90, ß-tubulin and calmodulin) were hybridised to chromosomal bands separated by pulsed-field gel electrophoresis. Three of those probes (actin type I, hsp90 and calmodulin) hybridised to only one chromosome and the remaining two (18S rRNA and ß-tubulin) hybridised to two chromosomes. In the first place, the hybridisation pattern obtained serves to dispel any doubt about the nuclear location of the smallest chromosome observed in the molecular karyotype of Perkinsus olseni. Additionally, it will be a reference for further analysis of karyotype polymorphisms in the genus Perkinsus.

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.

Is there a plastid in Perkinsus atlanticus (Phylum Perkinsozoa)?

Perkinsus atlanticus is a pathogenic protist that infects the clam Ruditapes decussatus. The recent proposal for the inclusion of the genus Perkinsus in a new phylum, Perkinsozoa, in the infra-kingdom Alveolata, gave rise to controversies whether this genus should form a phylum on its own. Molecular analysis of some conserved nuclear genes shows a closer proximity of the genus Perkinsus to the dinoflagellates than to the apicomplexans. Studies on extranuclear genomes, however, could also be very helpful for a more precise definition of those phyla. In Perkinsozoa, there have been until now no reports about the isolation of mitochondria as well as no conclusive results about the presence of any plastids, therefore a comparison with the data already obtained in Apicomplexa and Dinoflagellata has not yet been possible. In this work, we identify a plastid in Perkinsus atlanticus, using ultrastructural techniques and inhibition growth tests. It will be important to analyze the plastid genome at a molecular level, in order to confirm if the plastid in Perkinsus is more similar to those of Dinoflagellata or Apicomplexa. Such information will doubtless contribute to a more precise determination of the phylogenetic position of the genus Perkinsus.