Enhanced CO2-to-lipid bioconversion in oleaginous Coccomyxa subellipsoidea by high light intensity: A comprehensive analysis of photosynthesis and carbon allocation

Oleaginous microalgae are promising candidates for biodiesel production due to their ability to convert CO2 into lipids. However, achieving simultaneous high biomass productivity and lipid accumulation remains a challenge. This study demonstrates that high light intensity (HL, 300 μmol/m2/s) significantly enhances both CO2 fixation and lipid synthesis in Coccomyxa subellipsoidea, a species with exceptional HL-tolerance. Under HL, 10.00 g/L biomass and 1.42 g/L/d CO2 fixation rate were achieved, with increases of 61.29% and 69.05% compared to moderate light intensity (ML, 80 μmol/m2/s); lipid content (51.84% DW) and productivity (401.75 mg/L/d) reached 1.6-fold and 2.7-fold improvements, overcoming the trade-off between biomass and lipid yields. Chlorophyll fluorescence analysis revealed HL-induced non-photochemical quenching enabled high CO2 fixation rate despite initial inhibition in photosystem II. Metabolome profiling revealed that proteins and free amino acids were degraded under HL, recycling nitrogen and carbon to redirect carbon flux toward lipid biosynthesis. HL optimized the fatty acid profile, improving the properties of fatty acid methyl esters that complied with biodiesel standards in China, USA and Europe. These findings establish HL-driven metabolic adaptation as a scalable strategy for CO2-to-lipid conversion, advancing carbon-neutral energy solutions and biofuels production.