1. Evaluation of Growth and Lipid Profiles in Six Different Microalgal Strains for Biofuel Production

Microalgae have been considered as potential feedstock to produce higher biomass and lipid content that is more suitable for biofuel production than traditional oleaginous crop plants, thus seems to be on niche of accumulating energy reserves to produce next-generation renewables such as biofuels and high-value chemicals, an essential alternative for diminishing fossil fuels. Evaluation of growth and lipid profiles of few oleaginous microalgae under nutrient deprivation will be the method to identify best industrial strain for production of biofuel precursors at commercial level. In the present study, we have evaluated six microalgal (both marine and freshwater) strains to find out their metabolic responses on growth and lipid profiles under different nutrient limitation (nitrogen, phosphorous, and/or sulfur) conditions. Our results demonstrate that all these strains showed severe growth hampering by stress phenomenon under nutrient deprivation except for phosphorous limitation, wherein the growth was normal among marine strains. Algal oils are rich in the triacylglycerols (TAGs) that serve as material for conversion to biofuels. Therefore, changes triggered by nutrient deprivation in these microalgae primarily increased TAG content (~up to 20 mg L⁻¹ D⁻¹) among marine strains under nitrogen and phosphorous limitation, whereas among freshwater strains, nitrogen limitation played a major role in increasing the TAG content (~up to 15 mg L⁻¹ D⁻¹). In conclusion, the biomass and lipid productivity among marine strains seems to be higher when compared to freshwater strains. Among all these six potential strains, we evaluated and identified a suitable marine strain Parachlorella kessleri with better biomass and higher lipid productivity for further characterization, which may be a critical step toward making algae-derived biofuels economically competitive for industrial production.