Barcoding ciliates: a comprehensive study of 75 isolates of the genus Tetrahymena

1 Department of Integrative Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada 2 United States Department of Agriculture, Agriculture Research Service, Western Regional Research Center, Food Safety and Health Unit, 800 Buchanan St, Albany, CA 94710, USA 3 Protistology Department, American Type Culture Collection, 10801 University Blvd, Manassas, VA 20110-2209, USA 4 Molecular Authentication Resource Center, American Type Culture Collection, 10801 University Blvd, Manassas, VA 20110-2209, USA Correspondence Denis H. Lynn ddr{at}uoguelph.ca The 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 that are close relatives of Tetrahymena , Colpidium campylum , Colpidium colpoda and Glaucoma chattoni , were selected. All tetrahymenines of unproblematic species could be identified to the species level using 689 bp of the cox1 sequence, with about 11 % interspecific sequence divergence. Intraspecific isolates of Tetrahymena borealis , Tetrahymena lwoffi , Tetrahymena patula and Tetrahymena thermophila could be identified by their cox1 sequences, showing