Chlorella sp. Mg shows special trophic transitions and biomass production

Abstract Most microalgae have strategy to switch their growing modes depending on the availability of light and carbon sources. Unexpectedly mixotrophic Chlorella sp. Mg produced much less biomass than its heterotrophic counterpart. Investigation of the growth, photosynthetic activity, and ROS levels showed that mixotrophic Chlorella sp. Mg did not repress its photosynthesis activity upon glucose treatment, which accumulated much higher amounts of ROSs than heterotrophic one. Treatment of DCMU to the mixotrophic cells decreased photosynthetic activity and ROS levels, resulting in an increase of biomass by 62%. Decreased light intensity for the mixotrophic cells led to a similar result to that of DCMU treatment. Transcriptomic analysis showed that mixotrophic Chlorella sp. Mg did not up-regulate the hexokinase (HXK) and did not down-regulate most photosynthesis-related genes. Taken together, the algal HXK gene may not act as a glucose sensor, which could lead to unbalance of carbon metabolisms and low biomass production.