Spermidine Enhanced Chlorella's Stress Resistance To Promote Growth Rate And CO₂ Fixation In Flue Gas Of Coal-fired Power Plant

The application of microalgae to fix CO₂ of coal-fired power plants is of great significance for mitigating the greenhouse effect and developing a low-carbon economy.However,the concentration of CO₂ in the flue gas of the power plant is about 10-15%,and it contains trace impurities such as SO₂ and NO.In addition,high light intensity stress conditions often exist in outdoor industrial production,which inhibits the growth and carbon fixation of microalgae.In this paper,spermidine increased the activity of antioxidant enzymes to reduce cell oxidative damage,enhanced the resistance of Chlorella and promoted its photosynthetic growth under the flue gas of coal-fired power plant.In order to promote the growth and carbon fixation of Chlorella in the presence of flue gas CO₂ from coal-fired power plants,spermidine was first used to enhance cellular resistance to a high CO₂ concentration?15%?and high light intensity?30,000 lux?.The biomass production of Chlorella increased first and then decreased with the increase of the spermidine concentration.The effect of spermidine concentration ?30 ?M on the growth of chlorella was small.When the concentration of spermidine was 300 ?M,the activity of superoxide dismutase?SOD?increased from 0.48 U/m L to 5.33 U/m L and expression levels of key enzymes of photosystems I and II,ATP synthase and transportase markedly increased,thereby enhancing the electron transport and energy supply that reduced oxidative damage.The accelerated cell division decreased the cell diameter from 3.64 ?m to 2.71 ?m and the fractal dimension from 1.60 to 1.49.Finally,an enhanced cellular resistance to the high CO₂ concentration and high light intensity increased the biomass yield from 0.11 g/L?0 ?M?to 1.71g/L?300 ?M?.Spermidine enhanced the cellular resistance to algae acidification and sulfite oxidation damage caused by SO₂ pollutants in coal-fired flue gas.Under high SO₂?192 mg/Nm3?conditions,the addition of spermidine containing alkaline amino groups effectively relieved algal acidification.The activity of superoxide dismutase?SOD?increased from 2.58 U/m L to 18.14 U/m L,which reduced the oxidative damage and pigment digestion of cells,significantly enhancing cell stress resistance.At the same time,the photosynthetic efficiency and pigment synthesis of the cells were improved,thereby promoting cell division,reducing the cell diameter by 25.95%,increasing the cell wall thickness by 29.68%,and finally increasing the yield of Chlorella carbonfixed biomass by 11.6 times.The use of spermidine enhanced the resistance of Chlorella to nitrite toxicity caused by NO pollutants in coal-fired flue gas and promoted its growth.400 mg/Nm3 NO inhibited the growth of microalgae;the addition of spermidine increased the activity of superoxide dismutase?SOD?and catalase?CAT?by 88.14% and 96.01%,respectively.Thereby,the ability to scavenge free radicals and photosynthesis of the cells was enhanced,and the chlorophyll a and b synthesis of chlorella cells were increased by 5.60% and 28.67%,respectively.Finally,the biomass yield of Chlorella was increased by 25.35%.