Study on high-CO2tolerant Scenedesmus sp. And its mechanism via comparative transcriptomic analysis

The emission of carbon dioxide (CO2) to the atmosphere at an increasingly high rate is the primary cause of global warming. Previous studies have mostly focused on low CO2 concentration inputs and the resulting CO2 concentrating mechanisms (CCM). However, there are relatively few reports on high-CO2 tolerant species and their tolerance mechanisms. In this study, Scenedesmus sp. was grown under 1-70 % CO2 conditions, and a transcriptomic analysis was performed to analyze the global gene expression profiles induced by extremely-high CO2 (70 %) relative to relatively-low CO2 (1%). Results showed that Scenedesmus sp. produced a maximum biomass of 3.92 g L-1 at 10 % CO2 and a biomass of 2.75 g L-1 at 70 % CO2. High relative CO2 levels (30-70 %) were favorable for accumulation of lipids and yielded a maximum lipid productivity of about 82.9 mg L-1 d-1. The abundance of genes related to oxidoreductase activities and photorespiration were stimulated under 70 % CO2 condition, which in turn led to overproduction of ROS. In addition, qPCR was used to validate the results from the transcriptomic analysis and found that most genes involving in the antioxidant system, such as CAT and SOD2, were upregulated around 16.5 times under the high CO2 treatments. In addition, the down-regulation of genes involved in CCM might ensure Scenedesmus sp. rapid adaption to the environmental signal to maintain microalgal growth through energy saving