Production characteristics of Porphyridium purpureum (Bory) Drew et Ross semi-continuous culture at low irradiance

The red microalga Porphyridium purpureum (Bory de Saint-Vincent, 1797) Drew et Ross, 1965 is of great interest to researchers as a source of various biologically valuable substances, with their content in cells being determined by cultivation conditions. Phycobiliproteins concentration in P. purpureum cells depends directly on nitrogen concentration in the culture medium and cell irradiance. Semi-continuous cultivation allows maintaining these parameters at a level given. The aim of the work was to study P. purpureum culture growth and B-phycoerythrin (B-PE) accumulation and production at low irradiance, with minimal rates of pigment photodestruction. P. purpureum semi-continuous (quasi-continuous) cultivation was carried out at a specific flow rate of 0.1 and 0.2 day−1 and mean surface irradiance of 5 and 25 W·m−2. P. purpureum culture productivity increased by 1.6–17 times both with a rise in surface irradiance 5 to 25 W·m−2 and an increase in the medium specific flow rate 0.1 to 0.2 day−1. Maximum productivity values for the experimental conditions (0.21 g·L−1·day−1) were recorded at 25 W·m−2 and 20 % medium specific flow rate, but those were 1.5–2 times lower than the precalculated ones. In P. purpureum cells, protein and B-PE concentrations decreased both with an increase in surface irradiance (by 15–20 %) and with a rise in a specific flow rate (by 1.5 times) for all the variants. The shifts in protein and B-PE concentration in P. purpureum culture had a unidirectional character as well; those mainly corresponded to the shift in the culture density. P. purpureum B-PE productivity increased by 1.5–1.9 times with a rise in surface irradiance 5 to 25 W·m−2. Maximum B-PE productivity (13 mg·L−1·day−1) was recorded for the variants of the experiment with a surface irradiance of 25 W·m−2 (0.1 and 0.2 day−1). An increase in specific irradiance of P. purpureum cells 7 to 26 W·g−1 resulted in a rise in biomass productivity by 2.6 times; in B-PE productivity, by 1.8 times; and in protein productivity, by 1.7 times. In the experiment, irradiance was the factor determining the production characteristics of P. purpureum culture, and it was confirmed by the data obtained.