Growth of Porphyridium purpureum (Porphyridiales, Rhodophyta) and Production of B-Phycoerythrin under Varying Illumination

Abstract

The red pigment B-phycoerythrin (B-PE) belongs to the group of phycobiliproteins (PBPs). It is a part of the light-harvesting pigment complex of the red microalga Porphyridium purpureum (Bory) Drew et Ross, and its amount in cells is determined by the level of irradiation and nitrogen supply. B-PE is a valuable natural pigment whose biotechnological potential is used in nutraceuticals, pharmaceuticals, food and cosmetic industries, and in biomedical research and clinical diagnostics. The dynamics of cell number and the content of photosynthetic pigments are quite often assessed in experiments with P. purpureum. The culture’s density is low in the majority of the experiments, although it is known that it can reach 10 g/L of dry matter. The aim of the study was to investigate the features of the accumulation and production of PBPs in a dense culture of P. purpureum under varying illumination. The molecular-genetic analysis confirmed the taxonomic affiliation of P. purpureum culture. Algae were grown in flat plate photobioreactors with an average illumination of 5, 10, and 15 klx. The dynamics of culture density, the content of B-PE, and production characteristics were used as indicators. It was shown that an increase in the microalgae culture density corresponding to the calculated nitrogen concentration in the nutrient medium was obtained only under illumination of 5 klx. Illumination increased to 10, and 15 klx caused a decrease in both the maximum and average productivities of the culture by 2.5–3.5 times. It was experimentally shown that the highest content of B-PE in the cells and culture of P. purpureum (5.5% of dry matter and 74 mg/L, respectively) was observed under illumination of 5 klx. The pattern of the change in B-PE content in P. purpureum culture was determined depending on the specific illumination of microalgae cells: the pigment concentration hyperbolically decreased with increasing specific illumination. Thus, the level of illumination of P. purpureum microalgae cells had a significant effect on the growth characteristics of the culture (growth rate, B-PE synthesis rate and yield): a lower level of surface illumination was preferred for P. purpureum cultivation. The approach proposed in the study allows one to reduce material costs during the cultivation of P. purpureum while maintaining a high growth rate of the culture.