Assessment of growth dynamics, metabolite production phasic analysis in microalgae Scenedesmus rotundus under varying...

Scenedesmus rotundus is a freshwater microalga with a wide range of biotechnological applications. This study elucidates the potential of Scenedesmus rotundus under varying pH (5,7,9,11, and 13) conditions focusing on growth profiles and metabolite dynamics. pH is a significant environmental factor in bioproduct industries, as it influences algal physiology and functional molecules. Results showed that extreme pH conditions (5 & 13) were not suitable microalgae growth and the highest biomass production of 4.3 g/L was observed in culture grown at pH 9. Biochemical profiling showed higher accumulation of proteins (1.58 ± 0.2 mg/L), carbohydrates (1.45 ± 0.1 mg/L) and total carotenoids (1.40 ± 0.005 µg/L) in culture grown at pH 9 during exponential phase. Whereas in the late exponential phase, maximum phenolic content (2.63 ± 0.05 mg GAE/g DW) and the highest antioxidative activity (ATBS radical scavenging rate = 86 %) were observed at pH 7 and pH 11 respectively. FAME analysis revealed higher portion of saturated fatty acid content (69.10 %) at pH 9, which resulted in better biodiesel quality with a higher cetane number (28.86) and lower iodine value (77.61 g I₂/100 g). FTIR spectral analysis provided further confirmation regarding pH-induced fluctuations in accumulation of biomolecules, such as pH 9 exhibited increased phosphate expression and membrane restricting and polysaccharide degradation was induced at pH 11. Phasic study provides a methodical way to enhance biomass and sustainable production of bioproducts. Therefore, the present study highlights that pH is a strong physiological phase-dependent regulator enabling selective enhancement of biomass, lipids, pigments, proteins, or antioxidants in Scenedesmus rotundus.