Enhancing Phycoerythrin Production of Marine Red Microalga Porphyridium purpureum with Low Salinity and Semi-Continuous Culture Strategy

<i>Porphyridium purpureum</i> can synthesize a high phycoerythrin content, which has strong potential application in nutrition, pharmaceuticals, and cosmetics. An effective culture strategy is the key to producing biomass of <i>P. purpureum</i> rich in phycoerythrin. However, there are still bottlenecks in the large-scale production of <i>Porphyridium</i>, such as nutrient supplementation and cultivation mode. In this study, <i>P. purpureum</i> SCS-02, isolated from the South China Sea, was used as experimental microalga strain. The effects of different salinity (10, 20 and 34 ppt) and semi-continuous culture on accumulation of biomass and phycoerythrin were investigated. The semi-continuous culture modes include recycled culture medium mode (RM) and fresh culture medium mode (FM). The results showed that low salinity (10 ppt) could enhance the accumulation of phycoerythrin, the content and yield of which were 8.39% DW and 160 mg L^-1, respectively. The yield of phycoerythrin of <i>P. purpureum</i> in semi-continuous culture with a 30% renewal rate of fresh culture medium was 253% higher than the batch culture. In summary, the semi-continuous culture strategy with fresh medium renewal under low salinity conditions increased the phycoerythrin yield to 641.47 mg after 30 days of cultivation, while exopolysaccharide accumulation was significantly reduced compared with batch culture. These results provide useful reference for optimizing culture strategies of <i>P. purpureum</i>, and may serve as a basis for future attempts to scale phycoerythrin production under industrially relevant conditions.