Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2007
Publication Date: 10/1/2007
Citation: Chantangsi, C., Lynn, D.H., Brandl, M. 2007. Barcoding Ciliates: a comprehensive study of 75 isolates of the genus Tetrahymena. International Journal of Systematic and Evolutionary Microbiology. 57:2412-25.
Interpretive Summary: DNA-based identification was proposed to serve as an alternative taxonomic approach for identifying a large number of species of organisms. It was suggested that a 5' 650-bp fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene could serve as a universal marker or “DNA barcode” for global biological identification of animal species. Preliminary studies have proven this gene to be a good taxonomic marker for discriminating animal species. Among living organisms, protists have long been recognized as an assemblage of organisms of complex forms and with polymorphic life histories. A majority of them are microscopic, and often specific staining procedures and electron microscopy are required to reveal key features for taxonomic identification. Thus far, a DNA barcoding approach using cox1 gene sequences has been applied to identify only a few groups of protists. To examine the usefulness of the cox1 barcode to ciliated protist species identification, species of the genus Tetrahymena were investigated
Technical Abstract: A mitochondrial cytochrome c oxidase subunit 1 (cox1) gene has been proposed as a DNA barcode to identify animal species. To test the applicability of the cox1 gene in identifying ciliates, 75 isolates of the genus Tetrahymena and three non-Tetrahymena ciliates – Colpidium campylum, Colpidium colpoda, and Glaucoma chattoni – were selected. All isolates of unproblematic species could be identified to the species level using 689 bp of the cox1 sequences with about 10% interspecific sequence divergence. Intraspecific isolates of Tetrahymena borealis, Tetrahymena lwoffi, Tetrahymena patula, and Tetrahymena thermophila could be identified by their cox1 sequences, showing <0.65% intraspecific sequence divegences. In addition, isolates of these species were clustered together on a cox1 neighbor-joining (NJ) tree. However, strains identified as Tetrahymena pyriformis and Tetrahymena tropicalis showed high “within-species” sequence divergence values of 5.01% and 9.07%, respectively, and did not cluster together on a cox1 NJ-tree. Our analysis also demonstrated low sequence divergences of <1.0% between some isolates of T. pyriformis and Tetrahymena setosa on the one hand, and some isolates of Tetrahymena furgasoni and T. lwoffi on the other, suggesting that the latter species in each pair is a junior synonym of the former. Overall, our study demonstrates the feasibility of the mitochondrial cox1 gene as a taxonomic marker for “barcoding” and identifying ciliated protists.