Utilizing carbon dioxide for thermostable phycocyanin production in Thermosynechococcus FACM4201

Thermophilic cyanobacteria are considered a promising alternative source of the natural blue colour, phycocyanin, which exhibits resistance to degradation at high temperatures. This study aims to investigate the utilization of carbon dioxide in the culture of Thermosynechococcus FA-CM-4201, an isolated strain from a hot spring in Thailand. The cells were grown in BG-11 with 1% CO₂ and modified BG-11 (M-BG-11) with various CO₂ concentrations (1%, 5%, and 10%) and incubated at 50 ^°C under a light intensity of 80 µmol photons m^-2 s^-1 for 7 days. The results revealed that introducing carbon dioxide into the culture medium led to increased yields of biomass (1.27 – 1.48 g L^-1) and phycocyanin (259.13 – 282.32 mg L^-1), approximately 1.5 and 2.1 times higher, respectively, compared to those achieved with BG-11 aerated with air. Furthermore, phycocyanin extracted from this cyanobacterium exhibited better thermostability than commercial phycocyanin. Subsequently, the experiment was expanded to outdoor conditions using M-BG-11 with 1% and 10% CO₂. The results showed that cells exhibit growth even under fluctuating conditions, although yields of biomass and phycocyanin were lower compared to the controlled laboratory conditions. Conclusively, carbon dioxide shows significant potential for producing thermostable phycocyanin, offering a cost-effective alternative. However, further research is required to assess the suitability of applying this strategy in outdoor conditions.