CO gradient domestication improved high-concentration CO tolerance and photoautotrophic growth of Euglena gracilis.

In order to improve CO biofixation efficiency of microalgae cultivated with coal-chemical flue gas, CO gradient domestication was employed to improve high-concentration CO tolerance and photoautotrophic growth of acid-tolerant Euglena gracilis. The dried biomass yield of photoautotrophic growth of E.gracilis increased from 1.09 g/L (wild-type strain) by 21 % to 1.32 g/L with CO gradient domestication to 15 % CO. The RuBisCO activity and biomass production of E.gracilis strain domesticated to 99 % CO were 2.63 and 3.4 times higher, respectively, than those of wild-type strain. The chlorophyll a and b contents were 2.52 and 1.79 times higher, respectively, than those of wild-type strain. Superoxide dismutase and catalase activities of 99 % CO-domesticated strain increased to 1.24 and 6 times, which reduced peroxide damage under high carbon stress and resulted in lower apoptotic and necrotic rates of domesticated strain. Thus, this work provides valuable guidance for CO fixation and adaptive evolution of E. gracilis in industrial flue gas.