Far-Red Component Enhances Paramylon Production in Photoautotrophic <em>Euglena gracilis</em>

In recent years, microalgae have gained significant biotechnological importance as a sustainable source of various metabolites of industrial interest. Among these, paramylon, a polysaccharide produced by the microalga Euglena gracilis, stands out for its diverse applications in biomedicine and pharmaceuticals. E. gracilis is an adaptable secondary eukaryote capable of growing photoautotrophically, heterotrophically and mixotrophically. During photoautotrophic growth, varying light conditions impact biomass and paramylon production. To investigate the effects of varying illumination more thoroughly, we designed and built a modular photobioreactor that allowed us to evaluate simultaneously the photoautotrophic growth of E. gracilis under twelve different light conditions: seven single spectrum lights (Ultraviolet, Royal Blue, Blue, Green, Red, Far-Red, and Infrared) and five composite spectra lights (3,000K, 10,000K, 30,000K white lights, Amber, and “Full-spectrum”). 24-day growing kinetics were recorded, and growth parameters calculated for each light regime. Additionally, pigment composition, photosystem II oxygen evolution, and paramylon production were determined under each light condition. The designed Ankaa photobioreactor enabled us to follow the adaptation of E. gracilis to several specific light regimes. Our results suggest a differential paramylon production profile between logarithmic and stationary phases that is strongly dependent on illumination. Additionally, far-red component enhances paramylon production, specially, during stationary phase.