Carbon Concentrating Mechanisms Research Of Chlorella Pyrenoidosa In Response To Different CO₂

The CO2 emission are gradually payed attention to with the rapid development of social economy and the industrialization. Compared with higher plants, microalgae can take the advantages of rapid growth rate, high biomass productivity, high value bio-products output as well as more than 10 times higher of carbon sequestration efficiency. Therefore, microalgae-mediated CO2 fixation has become a hot topic in recent years in the field of carbon reduction. However, the issue of efficiently capturing CO2 and its molecular foundation with high growth rate is still a key challenge.Here we proposed a topic to investigate the physiological and metabolic phenotype characteristics of photosynthetic growth process under different CO2 conditions, by presenting the foundation of whole-genome sequence of the oleaginous industrial strain Chlorella pyrenoidosa which is used as a model. On this basis, we illuminated the molecular mechanism of algal CCM regulating the expression and co-regulatory of CO2 bio-fixation network as well as key differentially expressed genes via high-throughput transcriptome sequencing under the high/low CO2 concentration. All of this lay the foundation of revealing the CO2-concentrating mechanism in Chlorella pyrenoidosa.Firstly, appropriate CO2 can keep the pH value stable in the neutral range and promote the growth of algal cells. The final cell dry weight reached more than 4 g/L under 1% and 5% CO2 and less than 1 g/L under the air, respectively. While almost all the algal cells were dead under the 100% CO2 because of the low pH. The chlorophyll content showed a trend of decline after rising at first as a whole. The content of total lipids was 1% CO2>5%CO2>air>10% CO2>20% CO2 in order.Secondly, switch from high (5%) to low (0.03%, air) CO2 concentration showed significant inhibitory effect on growth, and CO2 fixation rate declined 20%-30%. The intracellular carbon content maintained at about 45% while nitrogen content maintained at a constant level (2%-3%) after dropping from 8.5% to 4.5%. Moreover, the fatty acid composition of C16-C18 accounted for 72%-92% which indicated low CO2 concentration (0.03%) was suitable for the accumulation of saturated fatty acids.Finally, the center carbon metabolism, lipid synthesis and CCM differentially expressed genes were analyzed through high-throughput transcriptome sequencing with the transition. PEPC, MDH, ME in C4 pathway and some enzymes promoting pyruvate into oxaloacetic acid, malic acid, Co-A in TCA cycle were up-regulated under low CO2. Combined with the transcriptome sequencing and Real-time PCR analysis results, LCIB, HLA3, LCIA and two low-CO2 inducible protein gene (g4975, g7352) with remarkable experession changes were confirmed to be the key target genes of CO2-concentrating mechanism and molecular modification of Chlorella pyrenoidosa in the future.