A method of obtaining clones of
Tetrahymena pyriformis
on solid medium has been developed. The medium consists of a basal layer of 1.5% agar topped with 2 ml of 0.3% agar in sterile, plastic petri plates (100 by 15 mm). Both agar layers contain either 2% proteose peptone and 0.1% liver extract (complex medium) or defined medium supplemented with proteose peptone. After drying, 0.5 ml of liquid culture is spread evenly over the top agar, and the plates are then sprinkled lightly and evenly with autoclaved dry Sephadex G-25 (fine). Cell colonies can be observed after 5 days of incubation either by viewing with a microscope or without the aid of a microscope after staining. Plating efficiency is high on either complex or defined medium with a number of strains of
Tetrahymena
, both micronucleate and amicronucleate. Colonies can be picked and transferred to liquid culture for further growth. The existence of clones was demonstrated by plating a mixture of two different drug-resistant mutants. The method should prove useful in selective procedures for the isolation of mutants and for determining survival after treatments such as ultraviolet irradiation.
The effects of the chelating agent 8-hydroxyquinoline (Hq) on Tetrahymena thermophila were examined. Cell division was completely inhibited by 5 ug of Hq per ml. At this concentration deoxyribonucleic acid, ribonucleic acid, and protein syntheses were also completely and nonselectively inhibited. The inhibition was reversible after 6 h of Hq treatment. At concentrations above 20 /g/ml a 10,000
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