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 biological relevance of algae-derived marine oligosaccharides has potential significance in numerous applications of industrial biotechnology. Marine oligosaccharides are produced in algae naturally and/or by hydrolysis of derived polysaccharides. The potential of marine oligosaccharides is still unexplored, and these molecules, including their derivatives, are a versatile source of chemical diversity. In-depth knowledge on such molecules will provide novel insights, thus depicting their role in discovering mechanisms and the molecular functions within specific biological applications.

Tocopherols are the highly active form of the antioxidant molecules involved in scavenging of free radicals and protect the cell membranes from reactive oxygen species (ROS). In the present study, we focused on employing carbon supplementation with varying nitrate concentrations to enhance the total tocopherol yields in the native isolate Monoraphidium sp. CABeR41. The total tocopherol productivity of NR_HC (Nitrate replete + 3% CO₂) supplemented was (306.14 µg·L⁻¹ d⁻¹) which was nearly 2.5-fold higher compared to NR_VLC (Nitrate replete + 0.03% CO₂) (60.35 µg·L⁻¹ d⁻¹). The best tocopherol productivities were obtained in the NL_HC (Nitrate limited + 3% CO₂) supplemented cells (734.38 µg·L⁻¹ d⁻¹) accompanied by a significant increase in cell biomass (2.65-fold) and total lipids (6.25-fold). Further, global metabolomics using gas chromatography-mass spectrometry (GC-MS) was done in the defined conditions to elucidate the molecular mechanism during tocopherol accumulation. In the present study, the Monoraphidium sp. responded to nitrogen limitation by increase in nitrogen assimilation, with significant upregulation in gamma-Aminobutyric acid (GABA). Moreover, the tricarboxylic acid (TCA) cycle upregulation depicted increased availability of carbon skeletons and reducing power, which is leading to increased biomass yields along with the other biocommodities. In conclusion, our study depicts valorization of carbon dioxide as a cost-effective alternative for the enhancement of biomass along with tocopherols and other concomitant products like lipids and carotenoids in the indigenous strain Monoraphidium sp., as an industrial potential strain with relevance in nutraceuticals and pharmaceuticals.