- Abstract The cyanobacterium Spirulina platensis is one of the most promising sources of the polyunsaturated fatty acid γ-linolenic acid (GLA). The GLA content of Spirulina can be enhanced by cultivation under light-dark cycles in the laboratory or outdoors. Thus, in strain BP, the GLA content increased from 1.2 to 1.6% when cultivated under light-dark cycles. Moreover, in the derived mutant Z19, the GLA content reached 2.4% when cultivated outdoors. To the best of our knowledge, this is the highest GLA content ever reported for any alga.