The production of Spirulina platensis cells resistant to 8-azaguanine or beta-(2-thienyl)-DL-alanine following mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and UV-irradiation is described. The conditions for the mutagenesis were determined by monitoring cell viability and the appearance of the two types of mutants as a function of the stage of growth of the tricomes and the length and the conditions of the treatment. The optimal conditions for UV and MNNG mutagenesis were found to be 1-3 min irradiation and 30 min incubation with 50 micrograms MNNG/ml of tricomes derived from cultures entering stationary phase sonicated for 10 s and 5 s respectively. Under these conditions beta-(2-thienyl)-DL-alanine-resistant mutants appeared at a frequency greater than or equal to 10(-4) and greater than or equal to 10(-5) following UV- and MNNG-mutagenesis, respectively. Mutants resistant to 8-azaguanine were found at a frequency approx. 10(-5) only after MNNG mutagenesis. A few chlorate-resistant mutants were also obtained following UV treatment.

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