The growth phase of the microalga Neochloris oleoabundans influences the production of useful biotechnological molecules and extracellular vesicles

Abstract Microalgae are versatile microorganisms that produce bioactive compounds with antioxidant, anti-inflammatory, and antimicrobial properties. Neochloris oleoabundans stands out for its adaptability and promising potential in a wide range of biotechnological applications, including the synthesis of high-value metabolites. Among the bioactive molecules of interest, extracellular vesicles (EVs) are gaining increasing attention for their potential in drug delivery and the development of novel therapeutic and healthcare products. The aim of this study is to investigate the microalga and how different growth phases can influence the yield of biologically active molecules with biotechnological relevance. For this reason N. oleoabundans (UTEX 1185) was cultivated for an unusually long period of 60 days. Measurements of the PSII maximum quantum yield indicated that the cultures remained in a healthy state even after prolonged cultivation, confirming the robustness of this strain. Biochemical characterisation of both the microalgal biomass and the conditioned medium was performed after 28 and 60 days of cultivation (corresponding to early and late stationary phases, respectively). The results suggest an enhanced production of high-value bioactive compounds during the early stationary phase, which is particularly advantageous given the higher biomass concentration at this stage. EVs were detected in the conditioned medium, with a higher abundance observed after 28 days. Transmission electron microscopy also revealed the presence of vesicles inside the cells, specifically located between the plasma membrane and the cell wall.