Carbon Dioxide Mitigation using Thermophilic Cyanobacteria

Microalgal biofixation of carbon dioxide (CO₂) in photobioreactors is a promising strategy for CO₂ mitigation, addressing the increased concerns over greenhouse gases (GHG). Previous studies on the subject focused mainly on the use of mesophilic cyanobacteria, not on thermophilic cyanobacteria. The specific objective of this study was to characterise Chlorogleopsis sp. (or SC2), a thermophilic cyanobacterial species collected from the Yellowstone National Park, as a potential candidate species for microalgal CO₂ biofixation. The results showed that: (1) the thermophilic SC2 grew very well at the elevated temperature of 50 °C and at an elevated CO₂ level of 5% (v/v supplemented); (2) the species also exhibited high light adaptability, growing successfully both under high light intensity (246·1 μmol m^-2 s^-1) and low light intensity (36·9 μmol m^-2 s^-1); (3) the optimum light intensity for SC2 among three light intensities tested was 200 μmol m^-2 s^-1; and (4) the maximum carbon-assimilation rate achieved by SC2 was 20·45 mg [C] l^-1 d^-1, occurring at 200 μmol m^-2 s^-1 and at 5% CO₂ level, and delivered at the low flow rate condition of 0·002 l [gas] l^-1 [medium] min^-1. Thus, SC2's high-temperature tolerance, high light adaptability, and reasonably high carbon-assimilation rate make SC2 a promising thermophilic cyanobacteria for use in a CO₂-mitigating photobioreactor.