The Physiological Effects of Organic Solvents, Plant Growth Regulators, and Fungicide on Auxenochlorella protothecoides

The cost of lipid production per biomass is an important factor for the expansion of the microalgal biorefinery industry. Some stressors and regulatory molecules, such as salicylic acid (SA), abscisic acid (ABA), indole-3-butyric acid (IBA), and carbendazim (CARB), can stimulate microalgal biomass and lipid quality, as well as improve their properties, by lowering unsaturated fatty acids, stimulating cell division and development, or causing oxidative stress. This study focused on identifying a microalgal growth condition that is compatible with enhanced lipid and biomass yields and high biodiesel quality while being highly resistant to stressors. Many carbon sources, such as glycerol (GLY), remain unclear as to how hormones and other stressors may stimulate growth under photoheterotrophic conditions, and GLY, also a regulator of fatty acid metabolism and hormone cross-talk, might enhance lipid accumulation under supplementation with phytohormones, fungicides, or even organic solvents. In addition, two organic solvents, three phytohormones, and one fungicide were evaluated, which are considered stressors to increase lipid productivity and the lipid quality of microalgae. Among the six stressors, 108 µM SA and 2.5 µM ABA combined with 8.4 g/L GLY resulted in the highest lipid productivity for Auxenochlorella protothecoides. In addition, supplementation with CARB concentrations of 260 µM and 1040 µM, ABA concentrations between 10 and 40 µM, and an SA concentration of 360 µM to GLY-modified Blue‒Green (BG11) medium provided lipid productivity to satisfy biodiesel standards. As a general statement, organic solvents, plant hormones, and fungicides at various concentrations in combination with GLY can enhance microalgal biomass productivity and lipid quality by promoting microalgal-based biodiesel.