Breeding of Nannochloropsis oceanica: Growth Performance and Nutritional Potential of Wild-Type and Mutant Strains from Laboratory to Pilot Scale

The marine microalga Nannochloropsis oceanica is a promising organism for sustainable production of lipids, omega-3 fatty acids, and biomass with a high nutritional value. We demonstrate UV mutagenesis combined with visual screening to generate novel non-GMO strains with improved industrial traits. Four mutants displayed altered pigmentation and/or enhanced growth after UV treatment, of which mutants M34 and M181 were selected for detailed characterization. Mutant M34 displayed enhanced biomass productivity under high light conditions (400 µmol m−2 s−1) in small-scale photobioreactor cultivations, indicating improved tolerance to elevated irradiance. Pigment analyses revealed reduced levels of several xanthophyll carotenoids, suggesting altered light adaptation and photoprotective responses. However, the improved growth phenotype was not consistently maintained at medium and pilot scale, highlighting the strong influence of cultivation conditions on measured strain performance. Mutant M181 exhibited strongly reduced chlorophyll content, accompanied by impaired growth at elevated light intensities. Pilot-scale cultivation demonstrated significantly increased lipid accumulation, reaching up to 25% of dry matter compared to 17% in the wild type. While M181 showed an unaltered composition of amino acids, total fatty acids, and eicosapentaenoic acid, we found elevated vitamin D3 accumulation after UVB exposure and significantly higher menaquinone-4 (MK-4) bioaccessibility, potentially improving the nutritional functionality. The results demonstrate that UV mutagenesis combined with simple visual screening is an effective strategy to generate N. oceanica strains with altered biomass composition and growth performance. Our study shows the importance of evaluating mutants under industrially relevant conditions, as phenotypes observed at laboratory scale may not translate well to pilot-scale systems.