Time-resolved transcriptome analysis of Scenedesmus obliquus HTB1 under 10% CO2 condition.

Abstract

Certain microalgal species can grow under high CO2 concentrations providing potential for mitigating CO2 pollution in flue gas produced by power plants. Microalga Scenedesmus obliquus strain HTB1 was isolated from the Chesapeake Bay and grow rapidly in a high level of CO2 . However, little is known about the molecular responses of HTB1 to high CO2 levels. Here, we investigated how HTB1 responds to 10% CO2 using the time-resolved transcriptome analysis. Gene expression profiles indicated that HTB1 responds quickly (in 2 h) and becomes adaptive within 12 h when exposed to 10% CO2 . Interestingly, certain genes of light-harvesting, chlorophyll synthesis and carbon fixation (i.e. rbcS) were up-regulated at 10% CO2 , and these functional responses are consistent with the increased photosynthesis efficiency and algal biomass under 10% CO2 . Nitrate assimilation was strongly enhanced, with amino acid biosynthesis and aminoacyl tRNA biosynthesis genes being markedly up-regulated, indicating that HTB1 actively takes up nitrogen and accelerates protein synthesis at 10% CO2 . Carbon metabolism including fatty acid biosynthesis and TCA cycle was enhanced at 10% CO2 , supporting the earlier observation of increased lipid content of Scenedesmus sp. under high CO2 levels. Interestingly, key genes like RuBisCO (rbcL) and carbonic anhydrase in carboxysomes did not respond actively to 10% CO2 , implying that exposure to 10% CO2 has little impact on the carbon concentrating mechanisms and CO2 fixation of the Calvin cycle. It appears that HTB1 can grow rapidly at 10% CO2 without significant metabolic changes in carbon fixation and ATP synthesis.