Growth and product formation of Porphyridium purpureum

A mathematical model was developed to describe the influence of cultivation conditions on the growth and formation of macromolecular products of the red alga Porphyridium purpureum. Several macroscopic regulation mechanisms were shown to influence product formation. The growth and formation of pigments and polysaccharides and the release of polysaccharides were studied in different photobioreactors under batch and continuous cultivation conditions. The light intensity tested ranged from the compensation point to conditions nearly saturating for growth. Temperature, gas and the medium were kept constant during the experiments in the photobioreactors, but were varied in supplementary experiments in shaken flasks. A non-linear relationship was found between the biomass concentration and the polysaccharides excreted to the medium. Light intensity did not influence polysaccharide formation directly, but was the main external factor influencing pigment composition. These two factors are considered in a structural model of functional macromolecules to give a proper description of the product regulation. Based on the experimental results a model is proposed that describes the formation of functional macromolecules in this alga.