Sustainable process for increased lutein production in green microalga Coelastrella thermophila

Coelastrella thermophila represents a highly promising microalgal platform for sustainable lutein production due to its thermotolerance, high biomass productivity, robust carotenoid biosynthetic capacity, and compatibility with carbon capture technologies. The integration of optimized cultivation strategies, advanced bioprocess engineering, and downstream processing technologies is expected to accelerate the commercialization of lutein production from this microalga, contributing to the growing global demand for natural, environmentally friendly carotenoid products.

Coelastrella thermophila P2, isolated from marine brine samples collected at the CSIR-CSMCRI Experimental Salt Farm, was maintained axenically on Bold Basal Medium (BBM) and cultivated using a two-stage strategy to enhance lutein production. Initially, the strain was grown in modified CSMCRI P2 (Zarrouk's) medium under controlled conditions (16 h light/8 h dark) to maximize biomass accumulation. During the second stage, late logarithmic-phase biomass was transferred to alkaline medium under optimized reactive oxygen species (ROS)-inducing conditions, combining high salinity and elevated pH to stimulate carotenoid biosynthesis. Purification of lutein was achieved using Fe₃O₄ magnetic nanoparticles as selective adsorbents, followed by magnetic separation and desorption with tetrahydrofuran (THF). The purified lutein was characterized by UV-Vis spectroscopy, nuclear magnetic resonance (NMR), and high-performance liquid chromatography (HPLC), while the synthesized Fe₃O₄ nanoparticles were characterized using Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD).

Under optimized conditions, Coelastrella thermophila provided a biomass concentration of 1.1 g/L with a highly enriched lutein fraction representing approximately 10% of the total carotenoid fraction, as confirmed by UV-visible spectroscopy, HPLC and NMR. Surprisingly, in the current process, Coelastrella thermophila produced only lutein, a carotenoid, at a higher concentration, thereby reducing downstream production costs. Further at downstream, reusable Fe3O4 nanoparticles were used to purify separate lutein from other cellular impurities in a cost-effective manner. This is the first report on biomanufacturing a major single pigment at higher concentration from microalgae, which can provide new insights into microalgal pigment production.