Enhancing biodiesel production in Anabaena sphaerica MBDU 105: exploring photo-, hetero-, and mixotrophic cultivation for biomass, lipid, and fuel properties

Cyanobacteria offer a promising alternative to conventional petro-diesel, presenting a potential pathway toward a cleaner environment. Twenty-six heterocystous cyanobacterial strains were tested in our previous study; the high lipid-yielding strain Anabaena sphaerica MBDU 105 (hereafter Anabaena 105) evidenced appropriateness for biodiesel production was selected to uplift biomass and lipid production. The current investigation examines the cultivation of the high lipid-yielding strain Anabaena 105 under three different modes: photoautotrophic, heterotrophic, and mixotrophic. The study delves into various aspects including biomass production, lipid yield, pigment, biomolecules, and fuel quality. Exogenous addition of glucose in media increased biomass productivity by 8.6-fold and 5.6-fold in mixotrophic compared to photoautotrophic and heterotrophic modes, respectively. The maximum lipid productivity of 31.64 ± 0.52 (mg/L/day) and lipid content of 39.21± 0.11 (% dwt) at 6 (g L⁻¹) glucose concentration was attained in mixotrophic mode. The highest palmitic acid (59.88–76.25%) concentration was obtained in a mixotrophic mode suitable for biodiesel production. Under heterotrophic conditions, the highest total protein content was observed, indicating significant potential for the utilization of cyanobacteria in food and feed applications. Biodiesel exhibits suitable fuel properties, including high cetane numbers, low unsaturation, and excellent lubricity, contributing to efficient engine performance and reduced emissions. To the best of current knowledge, this study represents the first validated report demonstrating that mixotrophic cultivation enhanced the lipid content and fuel quality of Anabaena 105. This study highlights that utilizing cost-effective organic carbon sources such as glucose in mixotrophic cultivation has the potential to decrease the overall production costs of biodiesel, thus enhancing its economic viability and competitiveness compared to conventional diesel fuel.