Enhanced co-production of polysaccharide and phycoerythrin of Porphyridium purpureum via the synergistic effect of glycerol supplementation and increased irradiance in a stirred tank photobioreactor.

Background: To achieve efficient co-production of polysaccharides and phycoerythrin of Porphyridium purpureum in a 40 L stirred tank photobioreactor, a strategy of stepwise increasing irradiance and adding glycerol was proposed after optimization of environmental factors for microalgae growth.

Results: The results showed that the optimal temperature and NaCl concentration were 25 °C and 25 g L^-1, respectively. In addition, 100 and 13 μmol m^-2 s^-1 were identified as the optimal incident light intensity and volume-averaged light intensity, respectively. Among the four different culture strategies, compared with the traditional photoautotrophic culture with constant light intensity, the production of biomass, polysaccharides, and phycoerythrin were enhanced by 266.38%, 390.24%, and 61.76% under mixotrophic culture with stepwise increasing light intensity, respectively. The result demonstrated that the combination of glycerol supplementation and increased light intensity had a synergistic effect. Moreover, the production costs of polysaccharide and phycoerythrin decreased by 78.42% and 34.57% compared to the typical culture method (photoautotrophic culture with constant light intensity).

Conclusion: The strategy of mixotrophic culture with stepwise increasing light intensity not only enhanced the productivity of biomass and active substances, but also reduced production costs. © 2025 Society of Chemical Industry.