Self-Shading effect caused by high biomass concentration increased phycocyanin accumulation in Galdieria sulphuraria strain UTEX 2919 under autotrophic conditions

Abstract Galdieria sulphuraria exhibits metabolic flexibility, allowing it to grow heterotrophically or mixotrophically. Under these conditions, this microalga accumulates significant amounts of phycocyanin (PC). Additionally, autotrophic conditions combined with light limitation, PC accumulation may occur as a stress response. In this study, varying initial biomass concentrations of G. sulphuraria strain UTEX 2919 under autotrophic conditions were used to evaluate the effect of self-shading on PC accumulation. The effect of light exposure intensity and duration was also evaluated. Our results demonstrated that increased PC levels were directly correlated with prolonged exposure to light, reaching a maximum concentration of 7.75 mg PC g -1 dry cell weight (DCW) under continuous illumination at 140 μmol photons m -2 s -1 . Furthermore, a volumetric PC content of 17.12 mg L -1 and a specific PC productivity (Qp) of 4.28 mg L -1 day -1 , were achieved four days after inoculation under continuous light with a high initial biomass concentration. Overall, the results showed that a self-shading effect, based on a high inoculum concentration, enhanced PC synthesis in G. sulphuraria UTEX 2919.