Decreasing fossil fuels and its impact on global warming have led to an increasing demand for its replacement by sustainable renewable biofuels. Microalgae may offer a potential feedstock for renewable biofuels capable of converting atmospheric CO2 to substantial biomass and valuable biofuels, which is of great importance for the food and energy industries. Parachlorella kessleri, a marine unicellular green alga belonging to class Trebouxiophyceae, accumulates large amount of lipids under nutrient-deprived conditions. The present study aims to understand the metabolic imprints in order to elucidate the physiological mechanisms of lipid accumulations in this microalga under nutrient deprivation. Molecular profiles were obtained using gas chromatography–mass spectrometry (GC–MS) of P. kessleri subjected to nutrient deprivation. Relative quantities of more than 60 metabolites were systematically compared in all the three starvation conditions. Our results demonstrate that in lipid metabolism, the quantities of neutral lipids increased significantly followed by the decrease in other metabolites involved in photosynthesis, and nitrogen assimilation. Nitrogen starvation seems to trigger the triacylglycerol (TAG) accumulation rapidly, while the microalga seems to tolerate phosphorous limitation, hence increasing both biomass and lipid content. The metabolomic and lipidomic profiles have identified a few common metabolites such as citric acid and 2-ketoglutaric acid which play significant role in diverting flux towards acetyl-CoA leading to accumulation of neutral lipids, whereas other molecules such as trehalose involve in cell growth regulation, when subjected to nutrient deprivation. Understanding the entire system through qualitative (untargeted) metabolome approach in P. kessleri has led to identification of relevant metabolites involved in the biosynthesis and degradation of precursor molecules that may have potential for biofuel production, aiming towards the vision of tomorrow’s bioenergy needs.

The economic feasibility of the next-generation algal biofuels rely largely on the simultaneous production of high-value-added bioproducts (HVABs) in these photosynthetic cell factories. In this study, a newly isolated indigenous microalga belonging to the selenastraceae family Monoraphidium sp. (designated as CABeR41) has been isolated and characterized for its relevant biofuel precursors along with other HVABs, i.e., tocopherols. Our preliminary data sets demonstrate accumulation of higher amounts of lipids (266.6 mg g^–1 dcw) along with antioxidant molecules, such as α- and δ-tocopherols (456 μg g^–1 dcw and 974 μg g^–1 dcw), simultaneously when subjected to nutrient deprivation. The total tocopherol content has been increased in nitrogen-deplete conditions to 1450.24 μg g^–1 dcw from 638.2 μg g^–1 dcw. In conclusion, bioprospecting of new isolates from natural habitats and fine-tuning of specific conditions without compromising growth has potential for developing into a sustainable industrial strain for concomitant production of biofuels and bioproducts.