Engineering culture medium for enhanced carbohydrate accumulation in Anabaena variabilis to stimulate production of bioethanol and other high-value co-products under cyanobacterial refinery approach

The present investigation aims towards simultaneous increase in biomass and carbohydrate accumulation of Anabaena variabilis by formulating an optimal growth condition. Based on the individual factor studies, concentrations of three variables were optimized. An initial pH 8.9, 168.8 mg L−1 MgSO4, and 64.3 mg L−1 NaHCO3 were the best combination resulting in respective ∼1.5 and ∼2.4-fold higher biomass and total carbohydrate yield compared to BG-11-grown control. Carbohydrate profiling indicated ∼2.6-fold rise in the yield of reducing sugar and glycogen. The bioethanol yield was, therefore, enhanced by ∼2.5-fold, reflecting almost two-times higher the value obtained earlier using the biphasic approach. The optimized condition also heightened the yield of the co-products C-phycocyanin and sodium copper chlorophyllin by ∼3-fold, and poly-β-hydroxybutyrate and exopolysaccharides by ∼2.6 and ∼1.8-fold. A ∼60% greater earning was projected from both bioethanol and co-products using the optimal medium under the large-scale set-up compared to control. Thus the present work engineered a robust way to maximize bioethanol production within a shortened time spell, ruling out the constraints of nutrient starvation under biphasic strategies alongside economizing the production process incorporating cyanobacterial refinery approach. Additionally, the details on photobioreactor prospects and sustainability assessment using ‘Water footprint’ would be beneficial for future research.