Characterization of a nicotine-resistant mutant of Chlorella emersonii

A nicotine-resistant mutant of the unicellular green microalga Chlorella emersonii was induced by UV light followed by selection in the presence of nicotine. In comparison with the wild type cells, the mutant cells produced lower amounts of the photosynthetic pigments chlorophyll and carotenoids, the culture appearing paler. However, in the presence of nicotine, the photosynthetic potential of the mutant was higher than that of the wild type. The effect of nicotine on the inhibition of cyclization steps in the biosynthetic pathway of carotenoids and the consequent accumulation of the intermediates, γ-carotene and lycopene, in the nicotine-resistant mutant was similar to that of the wild type alga. In the presence of nicotine, the mutant was insensitive to light and responded to increasing concentrations of nitrogen in the growth medium by enhanced production of carotenoids, especially lycopene.