Temperature-dependent growth rate and photosynthetic performance of Antarctic symbiotic alga Trebouxia sp. cultivated in a bioreactor

Optimum growth temperature of Trebouxia sp. (re-classified as Asterochloris sp. recently), a symbiotic lichenized alga was evaluated using a batch culture cultivated in a bioreactor. The algae were isolated from lichen thalli of Usnea antarctica collected at the James Ross Island, Antarctica in February 2012. The algae were isolated under laboratory conditions and then cultivated on agar medium at 5°C. When sufficiently developed, the algae were suspended in a BBM liquid medium and cultivated in a photobioreactor for 33 days at either 15, or 10°C. During cultivation, optical density (OD) characterizing culture growth, and effective quantum yield of photosystem II (FPSII) characterizing photosynthetic performance were measured simultaneously. Thanks to higher FPSII values, faster growth was achieved at 10oC than 15oC indicating that Trebouxia sp. might be ranked among psychrotolerant species. Such conclusion is supported also by a higher specific growth rate found during exponential phase of culture growth. The results are discussed and compared to available data on temperature-dependent growth of polar microalgae.