COMPLEMENTATION ANALYSIS WITH NEW GENETIC-MARKERS IN PHAFFIA-RHODOZYMA

Isolation and characterization of auxotrophic mutants from wild-type a nd astaxanthin mutant strains of Phaffia rhodozyma is described. Diffe rences in survival were observed when u.v. irradiation of P. rhodozyma wild-type and astaxanthin mutant strains were incubated in the dark o r exposed to photoreactivating light. Ultra-violet mutagenesis was not effective to produce auxotrophic mutants in this yeast. Auxotrophic m utants were obtained with high efficiency through a nystatin enrichmen t procedure after a N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutagen ic treatment with a 0.12% survivor level. Stringent mutagenetic condit ions were needed to obtain P. rhodozyma auxotrophs. The most frequent mutants were ade(-) and met(-) in a rather narrow auxotroph spectrum. These results may be associated with a possible diploid condition of t his yeast. The high number of adenine auxotrophs obtained in relation to other auxotrophic mutants suggests the possibility of some degree o f heterozygosity in the wild-type strain UCD 67-385.