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Microalgae are a renewable resource that has the potential to supply the bioeconomy with drop-in fuels and biomaterials. However, economic feasibility requires high biomass and metabolite productivities and low cultivation cost before algae technologies can be commercialized. In this context, agricultural residues can serve as inexpensive sustainable sources of fermentable carbohydrates that may help algae meet those requirements. The present study investigates this approach by cultivating Chlorella vulgarisin the biomass hydrolysate of the inedible cover crop Brassica carinata, which is the residue remaining after oil is extracted from the seeds for manufacturing sustainable aviation fuel. The biomass, termed carinata meal, was pretreated with phosphoric acid and then enzymatically hydrolyzed by cellulase enzyme, resulting in readily fermentable renewable sugars, primarily glucose. C. vulgariscultivated in the hydrolysate showed higher lipid and lutein productivity compared to costlier commercial media. The optimal hydrolysate inclusion level of 50% (v/v) in BBM resulted in maximum lipid productivity of 75 mg L−1day−1and lutein productivity of 4 mg L−1day−1, which were threefold and sixfold, respectively, higher than in expensive BBM. Time course studies revealed distinct biochemical alterations in the algae, shedding light on the effect of culture medium on lipid and lutein biosynthesis. Moreover, the fatty acid profile of mainly C16:0, C16:1, C18:0, and C18:1 looked promising for biodiesel manufacture. As a result, inexpensive CM hydrolysate may be a viable renewable alternative to high-cost synthetic media for algae cultivation as it enhances biomass and product yields.

Graphical abstract:

Random mutagenesis is an effective strategy for enhancing cellular traits. In this study, we used the mutagen ethyl methanesulfonate to create fast-growing Nannochloropsis oculatamutants. 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 acontent, 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.