An exploration of lipid remodeling by microalga Chlamydomonas reinhardtii in autotrophic and mixotrophic cultivation for bioenergy prospects

Optimizing microalgal biomass production is pivotal for advancing sustainable bioenergy production, yet the inherent trade-off between growth and lipid accumulation under nutrient stress remains a significant hurdle. This study utilized C. reinhardtii to examine the effects of acetate supplementation on enhancing biomass under nitrogen sufficiency (Stage I) and lipid synthesis under nitrogen deficiency (Stage II) through growth kinetics, key enzymatic activities, and metabolomic profiling. Results displayed that at Stage I, optimum acetate supplementation increased the biomass concentration (4 fold), Chl a (∼3 fold), Fv/Fm (0.71) reflected in simultaneous increment in the enzymatic activities of isocitrate lyase (12.5 folds), malate synthase (20 folds), citrate synthase (9.75-fold) and RuBisCO (1.72-fold) against the control. However, acetate spiked culture (50 mM) led to a significant increase in the lipid content (44 % DCW) with enhanced activities of antioxidant enzymes (SOD, CAT, and APX) at Stage II. In addition, the increased ACCase and GPAT enzymatic activities substantiated the elevated fatty acid biosynthesis. Furthermore, high-resolution mass spectrometry (HR-MS)-based untargeted metabolomic analysis revealed a pronounced decline in polyunsaturated fatty acids and carbohydrates, concomitant with a substantial increase in saturated and monounsaturated fatty acids. This shift underscores a strategic metabolic reprogramming of the cellular carbon flux toward the biosynthesis of vehicular-grade lipids at Stage II cultivation. Collectively, these findings elucidate the intricate metabolic adjustments induced by acetate assimilation, presenting innovative strategies to enhance sustainable and economically viable microalgal biofuel production. • Acetate enhanced biomass (4 folds) and lipids (2.88 fold) over the control. • Acetate supplementation increased ICL and MS enzyme activity. • ACCase and GPAT enzyme activity were enhanced under N- starvation. • SOD, CAT and APX strengthened cell under N- starvation. • Increased SFA and reduced PUFA suggested lipid remodeling.