Enhanced lipid production in Chlorella vulgaris via indole-3-acetic acid salt stress in a two-stage culture for biofuels

Utilizing saline wastewater for the cultivation of microalgae represents a viable approach to decrease the production costs associated with microalgae-derived biodiesel. In this study, a new method of combining plant hormones with two-stage culture was proposed to drive efficient lipid production of microalgae under salt stress. The findings indicated that the introduction of 40 mg·L⁻¹ of indole-3-acetic acid (IAA) during the initial phase resulted in optimal cell density and lipid productivity of Chlorella vulgaris under conditions of 10 g·L⁻¹ NaCl stress, achieving values of 65.15 × 10⁶ cells·mL⁻¹ and 47.62 mg·L⁻¹·d⁻¹, respectively. In the second stage, the application of salt stress was repeated, leading to a lipid productivity of 56.17 mg·L⁻¹·d⁻¹, which represents an increase of 150.8 % compared to the untreated control group. Additionally, the proportion of saturated fatty acids rose to 29.26 %. Therefore, it has better combustion characteristics and stability. At the same time, the self-flocculation efficiency of microalgae also increased by 93.75 %. In addition, the regulatory mechanism of IAA on the growth and lipid accumulation of Chlorella under salt stress was discussed by quantitative analysis of the expression of genes related to signaling pathways and lipid biosynthesis in algal cells. This study provides ideas for microalgae to produce biodiesel and achieve sustainable development.