Improving the lipid content of Nannochloropsis oculata by a mutation-selection program using UV radiation and quizalofop

Microalgal biomass with a high content of lipids and fatty acids is generally obtained by culture under stress conditions, limiting its growth and increasing production costs. However, it is possible to obtain strains with higher content of some of the desired biochemical component through genetic improvement strategies. Our objective was to increase the lipid content through a mutation-selection procedure in the microalga Nannochloropsis oculata. This procedure involved the ultraviolet radiation exposure of microalgae at different times at different densities and selecting surviving colonies. Subsequently, they were exposed to the herbicide quizalofop-p-ethyl, selecting the colonies with lower survival. An 85% mortality in the UV-exposed microalgae was recorded at 120 min for 1 × 10⁵ cells mL⁻¹. Two strains surviving quizalofop-p-ethyl were obtained, with only one strain surviving in standard culture conditions. The comparison of the new and original strains shows that the growth rate of the new strain of N. oculata (S3) is greater than that of the original strain, and it also had a higher content of total lipids and some fatty acids such as (a) arachidonic acid (up to five times higher than original); (b) oleic and heptadecaenoic acids (more than double than the original strain); (c) elaidic, tridecanoic, and palmitic acids (slightly higher than the original strain). There were significant differences in composition profile (carbohydrates, proteins) in comparison with the original strain. In conclusion, the mutation-selection procedure for obtaining new strains with higher lipid content is suitable for the freshwater microalga N. oculata. It could be considered as a strategy of genetic improvement with potential for aquaculture, food, pharmaceuticals, and biodiesel.