Transcriptome and key genes expression related to carbon fixation pathways in Chlorella PY-ZU1 cells and their growth under high concentrations of CO2

Abstract

BackgroundThe biomass yield of Chlorella PY-ZU1 drastically increased when cultivated under high CO2 condition compared with that cultivated under air condition. However, less attention has been given to the microalgae photosynthetic mechanisms response to different CO2 concentrations. The genetic reasons for the higher growth rate, CO2 fixation rate, and photosynthetic efficiency of microalgal cells under higher CO2 concentration have not been clearly defined yet.ResultsIn this study, the Illumina sequencing and de novo transcriptome assembly of Chlorella PY-ZU1 cells cultivated under 15% CO2 were performed and compared with those of cells grown under air. It was found that carbonic anhydrase (CAs, enzyme for interconversion of bicarbonate to CO2) dramatically decreased to near 0 in 15% CO2-grown cells, which indicated that CO2 molecules directly permeated into cells under high CO2 stress without CO2-concentrating mechanism. Extrapolating from the growth conditions and quantitative Real-Time PCR of CCM-related genes, the K m (CO2) (the minimum intracellular CO2 concentration that rubisco required) of Chlorella PY-ZU1 might be in the range of 80–192 μM. More adenosine triphosphates was saved for carbon fixation-related pathways. The transcript abundance of rubisco (the most important enzyme of CO2 fixation reaction) was 16.3 times higher in 15% CO2-grown cells than that under air. Besides, the transcript abundances of most key genes involved in carbon fixation pathways were also enhanced in 15% CO2-grown cells.ConclusionsCarbon fixation and nitrogen metabolism are the two most important metabolisms in the photosynthetic cells. These genes related to the two most metabolisms with significantly differential expressions were beneficial for microalgal growth (2.85 g L−1) under 15% CO2 concentration. Considering the micro and macro growth phenomena of Chlorella PY-ZU1 under different concentrations of CO2 (0.04–60%), CO2 transport pathways responses to different CO2 (0.04–60%) concentrations was reconstructed.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0868-z) contains supplementary material, which is available to authorized users.

Enhanced biomass and CO2 sequestration of Chlorella vulgaris using a new mixotrophic cultivation method

“…Carbonic anhydrase (CA) and Rubisco are two key enzymes in the microalgae CO 2 concentrated mechanism (CCM) and play important roles in carbon transport and metabolism [34]. Therefore, the enzyme activity of CA and Rubisco was determined to characterize the effect of culture conditions on their CO 2 fixation process.…”

“…Most significantly, the transcript abundance of Rubisco (EC4.1.1.39) was down-regulated in the Calvin cycle, which catalyzes the carboxylation of ribulose 1,5-diphosphate with carbon dioxide in the Calvin cycle, and then is a key enzyme in the carbon concentrating mechanisms. In control group, the carbon source was insufficient and Chlorella need to activate the carbon concentrating mechanisms (CCM) to maintain normal cell growth [34,35]. But in the other three groups, there are enough carbon sources (CO 2 or acetic acids), the algae do not need to activate CCM, and therefore resulted in the down-regulation of Rubisco.…”

Characterization and optimization of endogenous lipid accumulation in Chlorella vulgaris SDEC-3M ability to rapidly accumulate lipid for reversing nightly lipid loss

“…It showed that a high CO 2 level stimulated lipid accumulation in microalgae in both light and darkness. High CO 2 level is considered a stress condition to promote lipid accumulation for some algae species [3, 31]. The other possible explanation is that lower O 2 partial pressure in higher CO 2 mixtures lowers the DO in the broths, which is lethal to algal cells [1] and eventually decreases the lipid content in microalgae cells [32].…”

Transcriptional analyses reveal the molecular mechanism governing shade tolerance in the invasive plant Solidago canadensis

“…Most of enzymes, such as phosphoribulokinase (PRK), phosphoglyceratekinase (PGK), RuBP carboxylase (rubisco), fructose‐bisphosphatase aldolase (ALDO), and glyceraldehyde phosphate dehydrogenase (GAPDH), plays an important role in the carbon fixation process (Huang et al, 2017; Silveira & Carvalho, 2016). Many DEGs, such as rbcL , PGK , GAPDH , and ALDO , were upregulated, which might enhance carbon synthesis in S .…”