Mutagenesis of the cyanobacterium Spirulina platensis by UV and nitrosoguanidine treatment

The production of Spirulina platensis cells resistant to 8-azaguanine or β-(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 μg MNNG/ml of tricomes derived from cultures entering stationary phase sonicated for 10 s and 5 s respectively. Under these conditions β-(2-thienyl)-dl-alanine-resistant mutants appeared at a frequency ≥10−4 and ≥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.