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 r ed alga Porphyridium purpureum. Several macroscopic regulation mechanisms w ere shown to influence product formation. The growth and formation of pigme nts and polysaccharides and the release of polysaccharides were studied in different photobioreactors under batch and continuous cultivation condition s. The light intensity tested ranged from the compensation point to conditi ons nearly saturating for growth. Temperature, gas and the medium were kept constant during the experiments in the photobioreactors, but were varied i n supplementary experiments in shaken flasks. A non-linear relationship was found between the biomass concentration and the polysaccharides excreted t o the medium. Light intensity did not influence polysaccharide formation di rectly, but was the main external factor influencing pigment composition. T hese two factors are considered in a structural model of functional macromo lecules to give a proper description of the product regulation. Based on th e experimental results a model is proposed that describes the formation of functional macromolecules in this alga.