Evaluating the potential of cytokinins for biomass and lipid enhancement in microalga Acutodesmus obliquus under nitrogen stress

Despite the significant reduction in biomass production, nitrogen stress is the most feasible strategy used for lipid enhancement in microalgae. The present study evaluates the potential for application of exogenous cytokinins to enhance the lipid accumulation and overcome the biomass production constraint of microalgae under nitrogen stressed conditions. This study was undertaken to investigate the effect of exogenously supplied cytokinins viz. kinetin and zeatin at various stages of growth on biomass and lipid productivities of Acutodesmus obliquus under nitrogen stress (ON). The effect of cytokinins on photosynthetic performance and biochemical composition of biomass was also evaluated. Enhanced biomass and lipid productivities were observed upon supplementation of the microalgae with selected cytokinins. Supplementation with kinetin (1 mg L⁻¹) and zeatin (0.1 mg L⁻¹) resulted in increased biomass productivity up to 50% and 60.7% respectively as compared to ON control. The highest biomass productivity of 176.79 mg L⁻¹d⁻¹was obtained with the addition of 0.1 mg L⁻¹zeatin (ON-Z_i) at the initial log phase. Cytokinin supplementation resulted in improvement in photosynthetic performance and exhibited higher rETR (relative electron transport rate) values as compared to ON control. The addition of kinetin (ON-K_m) at mid log phase and Zeatin (ON-Z_i) at initial log phase resulted in 64.95% and 63.06% increase in lipid productivity respectively, compared to ON control. Carbohydrate productivity was also found to be increased with zeatin (ON-Z_i) supplementation. The supplementation of cytokinins is an easy and scalable strategy for biomass and lipid enhancement in Acutodesmus obliquus under nitrogen stress.