Cellular Three-Dimensional Structure And Environmental Adaptation Mechanism Of Microalgae For Utilizing Flue-Gas CO₂ From Power Generation

The conversion and utilization of CO₂ from power generation flue-gas by microalgae through photosynthesis has the advantages of high carbon fixation efficiency,fast growth rate,strong environmental adaptability and high economic value of algal powder.It is an important technological choice for carbon reduction and conversion in China.However,the three-dimensional structure of microalgal organelles and the number of positional changes are not clear,nor is the regulatory mechanism of the multivariate competitive response to flue-gas CO₂ fixation by microalgae.Since nutrient concentrations are constantly changing during carbon fixation by microalgae.The coupling effect of optimal nitrogen and phosphorus concentration with CO₂ concentration adapted to the photosynthetic carbon fixation mechanism of microalgae has not been revealed.Under unfavorable conditions,such as high flue-gas temperature and N₂O,carbon fixation by microalgae growth is limited.In this paper,we used cryoelectron microscopy to reconstruct the three-dimensional structure of microalgae organelles and quantitatively analyze the effect of organelle changes on photosynthetic carbon fixation in microalgae.Protein sequencing was used to dissect the regulatory mechanisms of multiple competitions for carbon fixation in microalgae.It also revealed the characteristics of carbon accumulation,key enzymes and signaling mechanisms of photosynthesis in microalgae in response to different concentrations of CO₂ in response to changes in nitrogen and phosphorus concentrations.To analyze the adaptation mechanisms of microalgae to the stress of cellular carbon sequestration under the adverse conditions of high flue gas temperature and impurity N₂O.To reveal the influence of organelle microstructure on the photosynthetic conversion of CO₂ by microalgae.The three-dimensional structure of the dynamic growth of Chlorella organelles was completely reconstructed and quantitatively resolved using focused ion beam scanning electron microscopy.As chlorella progressed from the meristematic,elongation and mature stages,only one mitochondrion in each cell first fissioned into a single disc shape and then gradually fused and grew into a circular shape.The distance between the center of gravity of the chloroplast and the nucleus to the mitochondrion was shortened to 45.5% and 88.3% of the initial distance,respectively,to facilitate energy transfer.The pyrenoid duplex structure gradually evolved into a mature state of equal volume,which effectively promoted photosynthetic carbon fixation in chlorella.As the cell grows,euchromatin replicates,the nucleolus becomes progressively larger and the number of starch grains increases,but the average size of individual grains remains largely unchanged.Focused ion beam scanning electron microscopy combined with proteomics and phosphorylation modification techniques.It was used to reveal the mechanism of lipid synthesis at the protein and organelle level in Chlorella cells cultured at 15% CO₂ concentration in flue gas.The volume of chloroplasts and endoplasmic reticulum in subcellular organelles was increased by 47% and 306% respectively,improving the efficiency of starch grains conversion into lipids.Proteomics and modifications omics revealed that protein translation,ribosome structures and biosynthesis-related enzymes were significantly altered by phosphorylation,fine-tuning the biological functions of proteins.Increased protein modification of the pentose phosphate pathway,enhanced glycolysis and reduced gluconeogenesis pathways promoted lipid synthase expression and lipid accumulation（50% increase in lipid content）.This is consistent with enhanced carbon fixation,expanded subcellular organelles and improved lipid synthesis in photosynthesis.It was found that the optimal combination of CO₂ concentration and nitrogen and phosphorus nutrients significantly increased the expression of proteins related to photosynthesis and cellular respiration in microalgal cells.As well as improving the efficiency of photosynthetic electron transfer and carbon metabolism.Microalgal cells deficient in phosphorus and at optimal CO₂ concentrations expressed high levels of phosphate transporter proteins to improve phosphorus and nitrogen metabolism and maintain high carbon fixation capacity.However,inappropriate combinations of nitrogen,phosphorus and CO₂ concentrations caused more errors in DNA replication and protein synthesis,produced more lysosomes and phagosomes,and inhibited carbon fixation and biomass production in microalgae.The optimal CO₂ concentration under100% nitrogen and phosphorus nutrient conditions was 70% and microalgal biomass yield was 1.57 g/L.Proteomics reveals adaptation mechanisms of cellular carbon sequestration stress in microalgae at high flue gas temperatures.Microalgae showed a 26% increase in biomass production from carbon sequestration at an ambient temperature of 35°C compared to 25°C.The expression of photosynthesis-related proteins was up-regulated by 14.3%,increasing the electron transfer efficiency and photosynthetic oxygen release rate of photosynthetic carbon sequestration.The extracellular polymer content was increased by 2.71-fold.The cells took up more elemental Sulphur,and lysosomes and hydrogenases were up-regulated,promoting the removal of metabolic waste and damaged organelles as well as antioxidant defenses.However,the photosynthetic carbon fixation of the microalgae cells was severely inhibited at 42°C,and the cells were unable to maintain normal growth or even died by apoptosis.The mechanism of the effect of N₂O impurities in the flue gas of circulating fluidized bed boilers on carbon sequestration by microalgae was investigated.The dry weight of microalgal biomass increased by 13.8%,chlorophyll a by 19.8% and protein content by 1.97-fold when the N₂O concentration was 80 ppm.Thereby effectively improving the photosynthetic electron transfer efficiency and photosynthetic oxygen release rate.N₂O increased superoxide dismutase activity in microalgae cells by 2.21-fold,significantly enhancing the antioxidant capacity of the cells.N₂O restricted glycolysis and the tricarboxylic acid cycle by influencing the intermediates of photosynthetic carbon fixation towards starch synthesis,resulting in lower respiratory oxygen consumption by microalgae.N₂O increased the carbon/nitrogen ratio of the cells and reduced extracellular polymers but upregulated the expression of metabolites such as methyl gallate,increasing the cellular anti-inflammatory and antibacterial capacity.Chlorophyll fluorescence quenching was reduced at N₂O concentrations up to300 ppm,and cells were photo inhibited,synthesizing reactive oxygen species,leading to oxidative damage and a 1.45-fold increase in malondialdehyde levels.The research results of this paper have been applied to the China Resources Group Haifeng Power Plant.The first technical demonstration of a column-type microalgae photoreactor for the reduction and utilization of flue gas CO₂ from a coal-fired power plant has been completed in China.The development of the column reactor with a compact structure and superior lighting conditions.This greatly reduced the footprint of the microalgae carbon sequestration equipment,breaking through the technical bottleneck of the traditional runway pond with its large footprint and low CO₂ utilization efficiency.The microalgae yield and CO₂ fixation per mu was over 5 times higher than that of the traditional runway pond microalgae reactor,realizing a microalgae carbon fixation process route for large-scale,high-efficiency and low-cost engineering implementation.The microalgae can produce nutritious food,functional feed and organic fertilizer,etc.,and achieve significant environmental,social and economic benefits.It has solved the common problem of poor economic efficiency of greenhouse gas CO₂ emission reduction in China and is able to achieve commercial operation of flue gas CO₂ emission reduction.