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Open Access Highly Accessed Research article

The Alveolate Perkinsus marinus: Biological Insights from EST Gene Discovery

Sandeep J Joseph125, José A Fernández-Robledo3, Malcolm J Gardner46, Najib M El-Sayed47, Chih-Horng Kuo28, Eric J Schott39, Haiming Wang1, Jessica C Kissinger12* and Gerardo R Vasta3*

Author Affiliations

1 Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA

2 Department of Genetics, University of Georgia, Athens, GA 30602, USA

3 Department of Microbiology and Immunology, University of Maryland School of Medicine, IMET, Baltimore, MD 21202, USA

4 J. Craig Venter Institute, formerly Institute for Genomic Research, 9712 Medical Center Drive, Rockville, MD 20850, USA

5 Current address: Department of Medicine, Division of Infectious Diseases, Emory University School of Medicine, Atlanta, GA 30322, USA

6 Current address: Seattle Biomedical Research Institute, Seattle, WA 98109, USA

7 Current address: Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, MD 20742, USA

8 Current address: Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA

9 Current address: University of Maryland Center for Environmental Science, IMET, Baltimore, MD 21202, USA

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BMC Genomics 2010, 11:228  doi:10.1186/1471-2164-11-228

Published: 7 April 2010

Abstract

Background

Perkinsus marinus, a protozoan parasite of the eastern oyster Crassostrea virginica, has devastated natural and farmed oyster populations along the Atlantic and Gulf coasts of the United States. It is classified as a member of the Perkinsozoa, a recently established phylum considered close to the ancestor of ciliates, dinoflagellates, and apicomplexans, and a key taxon for understanding unique adaptations (e.g. parasitism) within the Alveolata. Despite intense parasite pressure, no disease-resistant oysters have been identified and no effective therapies have been developed to date.

Results

To gain insight into the biological basis of the parasite's virulence and pathogenesis mechanisms, and to identify genes encoding potential targets for intervention, we generated >31,000 5' expressed sequence tags (ESTs) derived from four trophozoite libraries generated from two P. marinus strains. Trimming and clustering of the sequence tags yielded 7,863 unique sequences, some of which carry a spliced leader. Similarity searches revealed that 55% of these had hits in protein sequence databases, of which 1,729 had their best hit with proteins from the chromalveolates (E-value ≤ 1e-5). Some sequences are similar to those proven to be targets for effective intervention in other protozoan parasites, and include not only proteases, antioxidant enzymes, and heat shock proteins, but also those associated with relict plastids, such as acetyl-CoA carboxylase and methyl erythrithol phosphate pathway components, and those involved in glycan assembly, protein folding/secretion, and parasite-host interactions.

Conclusions

Our transcriptome analysis of P. marinus, the first for any member of the Perkinsozoa, contributes new insight into its biology and taxonomic position. It provides a very informative, albeit preliminary, glimpse into the expression of genes encoding functionally relevant proteins as potential targets for chemotherapy, and evidence for the presence of a relict plastid. Further, although P. marinus sequences display significant similarity to those from both apicomplexans and dinoflagellates, the presence of trans-spliced transcripts confirms the previously established affinities with the latter. The EST analysis reported herein, together with the recently completed sequence of the P. marinus genome and the development of transfection methodology, should result in improved intervention strategies against dermo disease.