ABSTRACT
Phycocyanin is a blue, photosynthetic pigment produced in phototrophic cultures of the cyanobacterium Arthrospira platensis and used in food and health products. Since the production process depends on externally suppled light, the productivity of biomass, and therefore also phycocyanin, is low in these cultures. Heterotrophic cultivation of the microalga Galdieria sulphuraria has emerged as a prospective alternative for production of phycocyanin. G. sulphuraria grows at pH 1–2, where most contaminating organisms will not grow; it takes up a large number of different carbon substrates, tolerates very high nutrient concentrations (e.g., up to 400 g L–1 glucose), and shows no sign of overflow metabolism, so biomass yields may exceed 0.5 g g–1 irrespective of to the substrate concentration. This alga is therefore excellently suited for high-cell-density cultivation at concentrations above 100 g L–1 and biomass productivities above 50 g L–1 day–1. Some isolates, including the well-characterized G. sulphuraria strain 074G, maintain phycocyanin synthesis even when grown heterotrophically in darkness. Although these cells contain less phycocyanin (10–30 mg g–1) than A. platensis (>100 mg g–1), the highest phycocyanin productivities in G. sulphuraria 074G cultures of 0.86 g L–1 day–1 are more than 10 times higher than in other organisms. The production is independent of climatic zone and season, and phycocyanin from cyanobacteria and G. sulphuraria share the same properties.
