Study On Accumulation,Metabolism And Antibacterial Activity Of Polysaccharides From Euglena Gracilis Based On Carbon Sequestration By Photosynthesis

With the acceleration of industrialization,the extensive use of fossil fuels,the gradual increase of CO₂emissions,the increase of CO₂concentration in the atmosphere and other factors have caused climate change,and global climate change has become one of the crises facing human society.In order to solve the global climate crisis,achieve carbon neutrality,promote the world energy transformation and promote sustainable development,microalgae reduction has become the frontier research focus and high-tech competition focus in the field of international emission reduction and new energy development.Microalgae can efficiently fix CO₂and convert solar energy into chemical energy through photosynthesis,and then directly convert the products of photosynthesis into high value-added substances to accumulate in cells.Therefore,using microalgae to reduce CO₂emission and produce high value-added products has great application prospects.In this study,Euglena gracilis was taken as the research object.By measuring the changes of cell density and photosynthetic pigment content of Euglena gracilis,the optimal illumination conditions were explored.Under the optimal illumination and photoperiod,the effects of CO₂aeration culture on the growth and photosynthesis of algae and on the polysaccharide content of Euglena gracilis were further explored.The response mechanism of Euglena gracilis under different CO₂aeration cultures was explored by transcriptome sequencing,and the antibacterial effect of Euglena gracilis polysaccharide was also discussed to explore the carbon assimilation products of Euglena gracilis.The main results are as follows:（1）The optimized light intensity（6000 lx）and light/dark ratio（15L:9D）were selected for aeration culture.The results showed that the growth of Euglena gracilis was the best under 5%CO₂aeration culture,with the cell density up to 8.14×10⁵cells/m L and polysaccharide content up to 30.76%.The effects of CO₂aeration on the contents of photosynthetic pigments and Malondialdehyde in eukaryotic algae;Malondialdehyde（MDA）content and superoxide dismutase（SOD）;The results showed that CO₂aeration culture reduced the content of photosynthetic pigment in the cell of Euglena gracilis.Meanwhile,MDA content and SOD activity indicated that Euglena gracilis gradually adapted to the CO₂aeration environment with the extension of culture time.（2）To explore the influence mechanism of CO₂aeration culture on the photosynthetic carbon fixation and polysaccharide content of Euglena gracilis,select aeration culture groups with the optimal growth concentration（5%CO₂）and the highest treatment concentration（20%CO₂）,and take air aeration culture as the control group,and conduct transcriptome sequencing.Five pathways including photosynthesis,photosynthetic antenna protein,photosynthetic carbon fixation,and starch and sucrose synthesis were selected for analysis according to physicochemical indexes and sequencing results.Compared with the control group,genes related to photoreactive protection mechanism were up-regulated in the CO₂aeration culture group.Analysis of the peroxisome pathway showed that the expression of SOD protein encoding gene was significantly up-regulated under 5%CO₂aeration culture,while the expression was not significant under 20%CO₂aeration culture.Combined with the physiological results,5%CO₂aerated culture stimulated the increase of intracellular metabolic activity of Euglena gracilis,produced a large number of metabolic reactive oxygen species,and caused the up-regulated expression of genes encoding SOD protein.（3）The antibacterial activity of polysaccharides extracted from Euglena gracilis was also discussed.Bacillus subtilis,Staphylococcus aureus,Pseudomonas aeruginosa,Trichoderma harzianum and Aspergillus niger were selected.Five kinds of common bacteria were cultured by adding psilocybin polysaccharide solution respectively.The results showed that Aspergillus niger and Bacillus subtilis had the highest sensitivity to polysaccharide,and the lowest inhibitory concentration was 25mg/m L.Followed by Pseudomonas aeruginosa and Aspergillus niger,the minimum inhibitory concentration was 50 mg/m L.It was also found that the polysaccharide could inhibit the protein synthesis of the bacteria and thus inhibit the growth of the bacteria.