` Adaptive evolution of microalgae Schizochytrium sp. under high temperature for efficient production of docosahexaeonic acid

Temperature is an important factor that not only affects cell growth, but also changes fatty acid composition in oleaginous microorganisms. Here, adaptive laboratory evolution (ALE) was performed in Schizochytrium sp. to enhance strain thermotolerance in docosahexaeonic acid (DHA) production. The adaptive strain showed higher growth rate and lower temperature sensitivity. Cell growth rate of the adaptive strain after 70 cycles at high temperature stimulation (ALE70) at 28 degrees C and 34 degrees C were 46.93% and 60.55% higher than that of original strain. Meanwhile, the reduction ratio of DHA yield from 28 degrees C to 34 degrees C of ALE70 decreased by 61.71%. Finally, lipid and DHA concentration at 34 degrees C reached 4.31 and 4.33 times of the starting strain. Further physiological analysis showed ALE70 generated less ROS, synthesized less HSP proteins, and produced more pigments, which might be related to the improved performance. This work increased the fermentation temperature by 5 degrees without affecting DHA production, which significantly reduced the energy consumption cost of the industrialization.