Biomass and phycobiliprotein production of Galdieria sulphuraria, immobilized on a twin-layer porous substrate photobioreactor

The extremophile red alga Galdieria sulphuraria was successfully grown immobilized in a twin-layer porous substrate bioreactor (TL-PSBR). A maximal biomass growth rate of 10 g dry weight m⁻² day⁻¹ was measured at a photon fluence rate of 200 μmol photons m⁻² s⁻¹ with addition of 1% CO₂ and a temperature of 34 °C. Under these conditions, a maximal biomass value of 232 g m⁻² was attained after 33 days of growth. Phycobilin productivity, however, was highest at a lower photon fluence rate of 100 μmol photons m⁻² s⁻¹ and reached a phycobilin value of 14 g m⁻², a phycobilin content in the biomass of 63 mg g⁻¹ and a phycobilin growth rate of 0.28 g m⁻² day⁻¹ for phycocyanin and 0.23 g m⁻² day⁻¹ for allophycocyanin. Addition of CO₂ was essential to enhance growth and phycobilin production in G. sulphuraria and further optimization of the cultivation process in the TL-PSBR appears possible using a multi-phase approach, higher growth temperatures and optimization of nutrient supply. It is concluded that autotrophic cultivation of G. sulphuraria in a TL-PSBR is an attractive alternative to suspension cultivation for phycobilin production and applications in bioremediation.