Dissecting Enhanced Carbohydrate and Pigment Productivity in Mutants of Nannochloropsis oculata Using Metabolomics and Lipidomics

Random mutagenesis is an effective strategy for enhancing cellular traits. In this study, we used the mutagen ethyl methanesulfonate to create fast-growing Nannochloropsis oculata mutants. When cultivated in a photobioreactor with a diel cycle, two mutants exhibited 2.2-fold higher carbohydrate productivity and 3.5-4.0-fold higher pigment productivity than the wild type, while one of them also showed 2.5-fold higher lipid productivity. A comprehensive physiological, metabolomic, and lipidomic study showed that the mutants had high levels of glucose-, galactose-, and xylose-based carbohydrates. Their high growth rate was attributed to increased chlorophyll a content, improved nitrogen assimilation, storage, and recycling, and low monogalactosyldiacyl glycerol/digalactosyldiacyl glycerol ratio, which was responsible for higher biomass productivity. The investigation revealed upregulation of lipid precursors, shedding light on high lipid accumulation. The derived algae strains are capable of increasing the biosynthesis of value-added storage molecules without impairing growth, rendering them promising candidates for commercial development in future biorefineries.