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are prominent members of 
the ciliate communities in water treatment plants 
(Curds, 1969, 1975b). The peritrichs are a particu-
larly important group, responsible for clarification 
of the water by their bacterivory (Fried et al., 2000; 
Lee, Basu, Tyler, & Wei, 2004; Martin-Cereceda 
et al., 2001a, 2001b; Rivera et al., 1988). The wide-
spread distribution of scuticociliates , hymenos-
tomes , and peritrichs , and the ease with which 
they can be cultivated has also established them as 
model organisms in the assessment of toxicants . 
 Hymenostomes , in particular Tetrahymena and 
Colpidium , have often been used in a wide vari-
ety of applications testing a diversity of toxicants 
from heavy metals to detergents to hydrocarbons . 
Recent reviews discuss the various end-points used 
(Gilron & Lynn, 1996; Sauvant, Pepin, & Piccinni, 
1999). These include growth inhibition (Dive et al., 
1991; Miyoshi et al., 2003; Schultz, 1997; Schultz 
& Dumont, 1977; Zilberg & Sinai, 2006), survival 
(Komala, 1993; Madoni & Romeo, 2006; Sartory 
& Lloyd, 1976; Schlenk & Moore, 1994), respiration 
(Slabbert, Smith, & Morgan, 1983), chemosensory 
behavior (Berk, Gunderson, & Derk, 1985; Gilron 
et al., 1999; Roberts & Berk, 1990), mutagenicity 
(Smith-Sonneborn, 1981), and ingestion rate 
(Juchelka & Snell, 1995). Recently, viability has 
15.7 Other Features 325
been assessed using fluorescent dyes indicative 
of the integrity of particular cell functions (Dayeh 
et al., 2004; Dias et al., 2003; Wang, Zhang, & 
Wang, 2000). 
 Toxicants , such as heavy metals and oils , are 
likely to impact communities, both in natural habi-
tats (Caron & Sieburth, 1981) and in waste-water 
treatment plants (Madoni et al., 1996). Nevertheless, 
the scuticociliate Uronema can acquire tolerance to 
 heavy metals (Berk et al., 1978), and this is likely 
due to the induction of metallothioneins , cysteine-
rich metal-binding proteins, which have been iden-
tified in Tetrahymena (Fu & Miao, 2006; Santovito 
et al., 2001). Nyberg and Bishop (1983) concluded 
that selective forces have operated to generate the 
variation in tolerance to heavy metals , particularly 
 copper and mercury , among stocks of Paramecium 
primaurelia . 
 Finally, Tetrahymena may be engineered to play 
a new role in the manufacturing of proteins for 
human use. Gaertig et al. (1999) were able to 
express the surface antigen of Ichthyophthirius 
multifiliis on the cell surface of Tetrahymena , 
demonstrating that Tetrahymena might be used 
as the “vehicle” to establish immunity to “ Ich ”
in fishes. Of more relevance to humans, Peterson 
et al. (2002) targeted a protein from the malaria par-
asite Plasmodium falciparum to the cell surface of 
Tetrahymena , demonstrating that this ciliate might 
be used in vaccine development against malaria . 
As a last example, Weide et al. (2006) have used 
Tetrahymena as an expression system for human 
enzymes and shown that a functional enzyme 
results. Is it too much of a stretch to imagine oligo-
hymenophoreans , like Tetrahymena , playing crucial 
roles in future human health applications?