Editing Tetrahymena (section)

=== Inducible trophic polymorphisms ===
''T. vorax'' is known for its inducible trophic polymorphisms, an ecologically offensive tactic that allows it to change its feeding strategy and diet by altering its morphology.<ref>{{cite journal |last1=Banerji |first1=Aabir |last2=Morin |first2=Peter J. |title=Trait-mediated apparent competition in an intraguild predator-prey system |journal=Oikos |date=May 2014 |volume=123 |issue=5 |pages=567–574 |doi=10.1111/j.1600-0706.2013.00937.x |bibcode=2014Oikos.123..567B }}</ref> Normally, ''T. vorax'' is a bacterivorous microstome around 60 μm in length. However, it has the ability to switch into a carnivorous macrostome around 200 μm in length that can feed on larger competitors. If ''T. vorax'' cells are too nutrient starved to undertake transformation, they have also been recorded as transforming into a third "tailed"-microstome morph, thought to be a defense mechanism in response to cannibalistic pressure. While ''T. vorax'' is the most well studied ''Tetrahymena'' that exhibits inducible trophic polymorphisms, many lesser known species are able to undertake transformation as well, including ''T. paulina'' and ''T. paravorax''.<ref>{{cite book |doi=10.1016/s0074-7696(01)12006-1 |chapter=Phenotype Switching in Polymorphic Tetrahymena: A Single-Cell Jekyll and Hyde |title=A Survey of Cell Biology |series=International Review of Cytology |year=2002 |last1=Ryals |first1=Phillip E. |last2=Smith-Somerville |first2=Harriett E. |last3=Buhse |first3=Howard E. |volume=212 |pages=209–238 |pmid=11804037 |isbn=978-0-12-364616-3 }}</ref> However, only ''T. vorax'' has been recorded as having both a macrostome and tailed-microstome form.

These morphological switches are triggered by an abundance of stomatin in the environment, a mixture of metabolic compounds released by competitor species, such as ''[[Paramecium]]'', ''[[Colpidium]]'', and other ''Tetrahymena''. Specifically, chromatographic analysis has revealed that [[ferrous]] iron, [[hypoxanthine]], and [[uracil]] are the chemicals in stomatin responsible for triggering the morphological change.<ref>{{Cite journal |last1=Smith-Somerville |first1=Harriett E. |last2=Hardman |first2=John K. |last3=Timkovich |first3=Russell |last4=Ray |first4=William J. |last5=Rose |first5=Karen E. |last6=Ryals |first6=Phillip E. |last7=Gibbons |first7=Sandra H. |last8=Buhse |first8=Howard E. |date=2000-06-20 |title=A complex of iron and nucleic acid catabolites is a signal that triggers differentiation in a freshwater protozoan |journal=Proceedings of the National Academy of Sciences |volume=97 |issue=13 |pages=7325–7330 |doi=10.1073/pnas.97.13.7325 |pmc=16544 |pmid=10860998 |bibcode=2000PNAS...97.7325S |doi-access=free }}</ref> Many researchers cite "starvation conditions" as inducing the transformation, as in nature, the compound inducers are in highest concentration after microstomal ciliates have grazed down bacterial populations, and ciliate populations are high. When the chemical inducers are in high concentration, ''T. vorax'' cells will transform at higher rates, allowing them to prey on their former trophic competitors.

The exact genetic, and structural mechanisms that underlie ''T. vorax'' transformation are unknown. However, some progress has been made in identifying candidate genes. Researchers from the University of Alabama have used cDNA subtraction to remove actively transcribed DNA from microstome and macrostome ''T. vorax'' cells, leaving only differentially transcribed cDNA molecules.<ref>{{Cite journal |last1=Green |first1=M. M. |last2=LeBoeuf |first2=R. D. |last3=Churchill |first3=P. F. |date=2000 |title=Biological and molecular characterization of cellular differentiation in Tetrahymena vorax: a potential biocontrol protozoan |journal=Journal of Basic Microbiology |volume=40 |issue=5–6 |pages=351–361 |doi=10.1002/1521-4028(200012)40:5/6<351::aid-jobm351>3.0.co;2-q |pmid=11199495 |s2cid=21981461 }}</ref> While nine differentiation-specific genes were found, the most frequently expressed candidate gene was identified as a novel sequence, ''SUBII-TG''.

The sequenced region of ''SUBII-TG'' was 912 bp long and consists of three largely identical 105 bp open-reading frames. A northern blot analysis revealed that low levels of transcription are detected in microstome cells, while high levels of transcription occur in macrostome cells. Furthermore, when the researchers limited ''SUBII-TG'' expression in the presence of stomatin (using antisense oligonucleotide methods), a 55% reduction in ''SUBII-TG'' mRNA correlated with a 51% decrease in transformation, supporting the notion that the gene is at least partially responsible for controlling the transformation in ''T. vorax''. However, very little is known about the ''SUBII-TG'' gene. Researchers were only able to sequence a portion of the entire open-reading frame, and other candidate genes have not been investigated thoroughly. mRNA and amino acid sequencing indicate that ubiquitin may play a crucial role in allowing transformation to take place as well. However, no known genes in the ubiquitin family have been identified in ''T. vorax''.<ref>{{cite thesis |id={{ProQuest|304234889}} |last1=Martin |first1=Teresa Dianne |date=1996 |title=Analysis of ubiquitin and differential gene expression during differentiation in Tetrahymena vorax }}</ref> Finally, the genetic mechanisms of the "tailed" microstome morph are completely unknown.