A Temperature-sensitive Mutant in Tetrahymena Pyriformis,

After treatment with nitrosoguanidine a mutation to temperature sensitivity was obtained in Tetrahymena pyriformis, syngen 1. The trait is controlled by a recessive allele, ts, at a locus linked to serotype locus T. I S is completely recessive, unlike any other allele studied in this organism, and the heterozygotes do not show vegetative assortment. The cross which revealed the linkage of ts and T failed to show evidence of the linkage of mt (mating type) and E-1 (esterase-I) which has been demonstrated in other crosses (ALLEN 19M; DOERDER 1972), but revealed a third case of linkage, involving mt and TO (tetrazolium oxidase). Taken together, these results are presumptive evidence for large interstrain differences in recombination properties within syngen 1. GENETIC studies of Tetrahymena have been hampered by the scarcity of identifiable loci and by the technical difficulties involved in the production of new mutants. In addition to the mutant strain already produced and described in detail (BLEYMAN 1968,1971), PHILLIPS (unpublished) recovered several deviant strains, but their infertility prevented genetic analysis. Recently, CARLSON (1971) has reported induced mutations, but his stocks are no longer available. The present study reports the occurrence of a mutant with decreased temperature tolerance. The mutant strain was isolated in 1969 while the author was a participant in an Undergraduate Research Training Program sponsored by the National Science Foundation and under the guidance of DR. DAVID L. NANNEY, Department of Zoology, University of Illinois. Since autogamy has not been detected in this species, new recessive mutations are readily accessible only when selfing strains or genomic exclusion (ALLEN 1967) can be harnessed to produce the homozygous recessive. The former stratagem was employed here. MATERIALS A N D METHODS Culture methods and procedures for the determination of serotypes, mating types, and electrophoretic variants closely follow those previously described (NANNEY and CAUGHEY 1955; PHILLIPS 1967). Cultures were grown at room temperature unless otherwise stated, in 1% proteose * This research was supported in part by a National Science Foundation Undergraduate Research Training Award to the School of Life Sciences, University of Illinois, and by Public Health Service Grant GM07779 to DR. D. L. NANNEY. Genetics 74: 107-114 May, 1973,