Barbara J. Sheppard1; Michael M. Miyamoto2; Debrata M. Mahapatra1; James Coleman1; Joselyn M. Hager1; Karen Kelley3
Abstract
A new pathogen recently discovered after importation into the USA in photosynthetic ornamental clams,1-3 Tridacna crocea, was investigated. The organism readily enlarged in alternative Ray's thioglycollate media (ARFTM), a diagnostic media specific for Perkinsus species, but did not propagate under standard culture conditions for known members of the Perkinsoa genus.4 Furthermore, a small percentage of P. olseni also found in the host tissues as a dual infection rapidly overgrew the unpurified cultures. Light microscopy and ultrastructural (TEM) examinations revealed tissue stages and morphology consistent with Perkinsus species trophozoites. Extensive phylogenetic and population genetic analyses using nuclear DNA sequences for the 5.8S ribosomal RNA (rRNA) gene and its surrounding internal transcribed spacers were performed. These analyses, which are based on 357 rRNA sequences, confirm that our new form is strongly diverged from other known members of the genus and belongs to a separate distinct evolutionary lineage. In turn, our population genetic (coalescent) analysis documents that limited gene flow is occurring between our new form and its closest known relative (P. olseni). On the basis of our behavior-in-culture experiments, morphology, and evolutionary inferences, we conclude that our new Perkinsus constitutes a previously unknown species of the genus. As such, we are in the process of providing a formal description and name for our new species.
Acknowledgments
The authors gratefully acknowledge the technical contributions provided by Lauren Roero, Paul Kuipers and George Papadi of the University of Florida, College of Veterinary Medicine.
References
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