Optimising thermal and irradiance conditions for enhanced oxygen production in Tetradesmus bajacalifornicus

This work evaluated the effect of culture temperature and irradiance on oxygen production rate and biomass productivity of the microalga Tetradesmus bajacalifornicus, an understudied species with potential for different biotechnological applications. The optimal conditions to increase oxygen productivity were determined using a photorespirometer using a response surface methodology. The highest oxygen production rate (250.0 mg O₂·g⁻¹·h⁻¹) was achieved at 38.1 °C and 500 µmol photons·m⁻²·s⁻¹, a value comparable to other high-performance strains. However, continuous exposure to 38.1 °C for extended periods led to photodamage and culture collapse, indicating the importance of balancing peak oxygen production rates with thermal tolerance. Further experiments showed that heating the culture for 1 h per day at 38.1 °C enhanced biomass accumulation by 12.5%, but longer exposures reduced oxygen production efficiency and growth. Milder temperatures (29.0 °C) did not alter oxygen production even with prolonged exposures, while 34.0 °C became detrimental beyond 1 h. These findings highlight the need to incorporate both temperature magnitude and exposure duration into microalgal growth models. Furthermore, Tetradesmus bajacalifornicus demonstrated robust adaptability to high irradiance and moderate thermal stress, making it a promising candidate for outdoor cultivation in warm, high-radiation environments.