The Distribution ofTetrahymena pyriformis1

Abundant and diverse Tetrahymena species living in the bladder traps of aquatic carnivorous Utricularia plants

Ciliates are unicellular eukaryotes known for their cellular complexity and wide range of natural habitats. How they adapt to their niches and what roles they play in ecology remain largely unknown. The genus Tetrahymena is among the best-studied groups of ciliates and one particular species, Tetrahymena thermophila, is a well-known laboratory model organism in cell and molecular biology, making it an excellent candidate for study in protist ecology. Here, based on cytochrome c oxidase subunit I (COX1) gene barcoding, we identify a total of 19 different putative Tetrahymena species and two closely related Glaucoma lineages isolated from distinct natural habitats, of which 13 are new species. These latter include 11 Tetrahymena species found in the bladder traps of Utricularia plants, the most species-rich and widely distributed aquatic carnivorous plant, thus revealing a previously unknown but significant symbiosis of Tetrahymena species living among the microbial community of Utricularia bladder traps. Additional species were collected using an artificial trap method we have developed. We show that diverse Tetrahymena species may live even within the same habitat and that their populations are highly dynamic, suggesting that the diversity and biomass of species worldwide is far greater than currently appreciated.

Natural populations and inbred strains of Tetrahymena

Tetrahymena typically is found in freshwater lakes, ponds, and streams in association with submerged or emergent vegetation. The genus consists of numerous breeding species with micronuclei and many asexual species without micronuclei. In summer months when most populations are at their peak, 30-50% of water samples may yield one or more species of Tetrahymena. This chapter describes both bulk and trapping procedures for collecting Tetrahymena and also evaluates barcode methods for species identification. The history and inbreeding of the laboratory model Tetrahymena thermophila is also discussed. There are numerous unresolved questions about Tetrahymena evolution and biogeography that may be solved by additional collecting.

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

The mitochondrial cytochrome-coxidase subunit 1 (cox1) gene has been proposed as a DNA barcode to identify animal species. To test the applicability of thecox1gene in identifying ciliates, 75 isolates of the genusTetrahymenaand three non-Tetrahymenaciliates that are close relatives ofTetrahymena,Colpidium campylum,Colpidium colpodaandGlaucoma chattoni, were selected. All tetrahymenines of unproblematic species could be identified to the species level using 689 bp of thecox1sequence, with about 11 % interspecific sequence divergence. Intraspecific isolates ofTetrahymena borealis,Tetrahymena lwoffi,Tetrahymena patulaandTetrahymena thermophilacould be identified by theircox1sequences, showing <0.65 % intraspecific sequence divergence. In addition, isolates of these species were clustered together on acox1neighbour-joining (NJ) tree. However, strains identified asTetrahymena pyriformisandTetrahymena tropicalisshowed high intraspecific sequence divergence values of 5.01 and 9.07 %, respectively, and did not cluster together on acox1NJ tree. This may indicate the presence of cryptic species. The mean interspecific sequence divergence ofTetrahymenawas about 11 times greater than the mean intraspecific sequence divergence, and this increased to 58 times when all isolates of species with high intraspecific sequence divergence were excluded. This result is similar to DNA barcoding studies on animals, indicating that congeneric sequence divergences are an order of magnitude greater than conspecific sequence divergences. Our analysis also demonstrated low sequence divergences of <1.0 % between some isolates ofT. pyriformisandTetrahymena setosaon the one hand and some isolates ofTetrahymena furgasoniandT. lwoffion the other, suggesting that the latter species in each pair is a junior synonym of the former. Overall, our study demonstrates the feasibility of using the mitochondrialcox1gene as a taxonomic marker for ‘barcoding’ and identifyingTetrahymenaspecies and some other ciliated protists.