Enhancing carotenoid production and exploring the potential use of microalga Desmodesmus cf. pleiomorphus DSHM22 as a biodiesel feedstock through photoheterotrophic cultivation

Improving biomass and value-added compound production is crucial for the industrial application of microalgae, achieved through the utilization of low-cost nutrients and various cultivation modes. This study aimed to enhance the biomass and biochemical production of the indigenous microalgae by comparing different cultivation modes. Among six algal strains obtained from the East Sea in South Korea, Desmodesmus cf. pleiomorphus DSHM22 exhibited the highest biomass productivity (0.0118 g L⁻¹ d⁻¹) and was selected for optimization. Algal growth responses were assessed under four commercially available soluble fertilizer media to identify a cost-effective nutrient substrate. The most effective fertilizer demonstrated 2.2-fold higher growth compared to the BG-11 algal medium after 14 days. Glucose was supplemented in the culture medium to evaluate organic carbon availability under light and dark conditions. While no growth responses were observed under glucose-supplemented dark condition, the highest biomass production (approximately 1.22 g L⁻¹) was achieved under glucose-supplemented light condition. The algal strain showed growth under both photoautotrophic (PA) and photoheterotrophic (PH) conditions, excluding the heterotrophic mode. Biochemical accumulations were compared by analyzing photosynthetic pigments and fatty acids under both PA and PH modes. The algal strain effectively produced lutein, neoxanthin, and omega-3, 6, and 9 fatty acids. Although PH condition yielded significantly higher biochemicals and lipid production compared to PA condition, both culture conditions exhibited similar fatty acid compositions and biodiesel properties. This study suggests that PH cultivation is an effective approach for producing value-added biochemicals and biodiesel using microalga D. cf. pleiomorphus DSHM22.