family have been identified in t. vorax. finally, the genetic mechanisms of the “tailed” microstome morph are completely unknown. metal resistance, gene & genome amplification other related species exhibit their own unique responses to various stressors. in t. thermophila, chromosome amplification and gene expansion are inducible responses to common organometallic pollutants such as cadmium, copper, and lead. strains of t. thermophila that were exposed to large quantities of cd2+ over time were found to have a 5-fold increase of mtt1, and mtt3 (metallothionein genes that code for cadmium and lead binding proteins) as well as cnbdp, an unrelated gene that lies just upstream of mtt1 on the same chromosome. the fact that a non-metallothionein gene on the same locus as mtt1 and mtt3 increased copy number indicates that the entire chromosome had been amplified, as opposed to just specific genes. tetrahymena species are 45-ploid for their macronucleus, meaning that the wild type of t. thermophila normally contains 45 copies of each chromosome. while the actual number of unique chromosomes are unknown, the number is thought to be around 187 in the mac, and 5 in the mic. thus, the ca2+ adapted strain contained 225 copies of the specific chromosome in question. this resulted in a nearly 28 times increase in detected expression levels of mtt1, and slightly less in mtt3. interestingly, when researchers grew a sample of the t. thermophila population in normal growth medium (lacking cd2+) for 1 month, the number of mtt1, mtt3, and cnbdp genes decreased to an average of 3 copies (135c). by 7 months in normal growth medium, the t. thermophila cells were found reduced to just the wild type copy number (45c). when researchers returned cells from the same colony to cd2+ medium, within a week mtt1, mtt3, and cnbdp genes increased to 3 copies once again (135c). thus, the authors argue that chromosome amplification is an inducible and reversible mechanism in the tetrahymena genetic response to metal stress. researchers also used gene-knockdown experiments, where the copy number of another metallothionein gene on a different chromosome, mtt5, was dramatically reduced. within a week, the new strain was found to have developed 4 novel genes from at least 1 duplication of mtt1. however, chromosome duplication had not taken place, as indicated by the wild-type ploidy and the normal quantity of other genes on the same chromosomes. rather, researchers believe that the duplication resulted from homologous recombination events, producing transcriptionally active, upregulated genes that carry repeated mtt1. enhanced motility and dispersal t. thermophila also undergoes phenotypic changes when faced with limited resource availability. cells are capable of changing their shape and size, along with behavioral swimming strategies in response to starvation. the more motile cells that change in response to starvation are known as dispersers, or disperser cells. while rates and levels of phenotypic change differ between strains, disperser cells form in nearly all strains of t. thermophila when faced with starvation. dispersers, and non-dispersing cells both become dramatically thinner and smaller, increasing the basal body and cilia density, allowing them to swim between 2 and 3 times faster than normal cells. some strains of t. thermophila have also been found to develop a single, non-beating, enlarged cilia that assists the cell in steering or directing movement. while the behavior has been shown to correlate with faster dispersal and form as a reversible trait in tetrahymena cells, little is known about the genetic or cellular mechanisms that allow for its development. furthermore, other studies show that when genetically variable populations of t. thermophila were starved, dispersal cells actually increased in cell length, despite still becoming thinner. more research is needed to determine the genetic mechanisms that underlie disperser formation. species in genus species in this genus include. tetrahymena americanis tetrahymena asiatica tetrahymena australis tetrahymena bergeri tetrahymena borealis tetrahymena canadensis tetrahymena capricornis tetrahymena caudata tetrahymena chironomi tetrahymena corlissi tetrahymena cosmopolitanis tetrahymena dimorpha tetrahymena edaphoni tetrahymena elliotti tetrahymena empidokyrea tetrahymena farahensis tetrahymena farleyi tetrahymena furgasoni tetrahymena glochidiophila tetrahymena hegewischi tetrahymena hyperangularis tetrahymena leucophrys tetrahymena limacis tetrahymena lwoffi tetrahymena malaccensis tetrahymena mimbres tetrahymena mobilis tetrahymena nanneyi tetrahymena nipissingi tetrahymena paravorax tetrahymena patula tetrahymena pigmentosa tetrahymena pyriformis tetrahymena rostrata tetrahymena rotunda tetrahymena setifera tetrahymena setigera tetrahymena setosa tetrahymena shanghaiensis tetrahymena sialidos tetrahymena silvana tetrahymena skappus tetrahymena sonneborni tetrahymena stegomyiae tetrahymena thermophila tetrahymena tropicalis tetrahymena vorax in education cornell university offers a national institutes of health (nih) funded program through the science education partnership award (sepa) program called advancing secondary science education thru tetrahymena (asset). the group develops stand-alone labs or lessons using tetrahymena as training modules that teachers can use in classes.