| At present,CuSO4 is used in large quantities during the cultivation of microalgae causing different levels of Cu2+residues.Copper mining also allows copper to enter the offshore ecosystem along with underground rivers and inland rivers.However,despite being a trace element,copper is required for the growth of microalgae.It is also an important coenzyme factor in many metabolic pathways.Chlorella strains are known to stimulate their growth under certain toxic conditions.Compared to marine microalgae,deserts and polar species of this microalgae are more resistant to stress and can tolerate more severe temperature changes,higher salinity and glare Irradiation.However,the response of Chlorella to extreme environments of heavy metal ion contamination has not been studied.Hence,this study deems that it is necessary to explore the influence of heavy metal ions on the growth and lipid production of Chlorella in such an extreme environment.In this experiment,Chlorella pyrenoidosa was compared with desert and polar chlorella to study the differences in growth and physiological and biochemical indexes under copper ion stress conditions.(1)The growth of the three Chlorella strains at concentrations of 0.157 mM,0.314 mM,0.393 mM,1.57 mM,6.28 mM,12.56 mM,25.12 mM,and 50.24 mM has been investigated.A certain promotion effect has been observed,in which the biomass and oil content of Chlorella in the desert increased by 13.1%and 9.81%respectively,and the biomass and lipid content of Chlorella pyrenoidosa increased by 9.37%and 8.09%,respectively.Quantity and lipid content of the polar Chlorella has increased by 9.23%and 8.21%,respectively,at 12.56mM,while the lipid content of Chlorella desertensis increased by 25.92%.This shows that certain copper ion stress can promote the growth and oil content of these three Chlorella strains.(2)Under such condition of Cu2+ stress,the three Chlorella strains have revealed their protective mechanism:Chlorella pyrenoidosa shows a high growth rate under Cu2+ stress;whereas the desert and polar Chlorella tend to increase their polysaccharides and proteins content with the increase in Cu2+,especially the content of extracellular polysaccharides and intracellular proteins indicating that these two strains of Chlorella have good biosorption capacity Hence,they prevent the of absorption Cu2+by secreting metal binding proteins and polysaccharides to ensure normal physiological function.(3)The growth rate of the three Chlorella strains can be effectively promoted under high nitrogen conditions.The initial concentration of nitrogen was 117.6 mM.Compared with the control group,the specific growth rates of Chlorella pyrolense,Chorella-Arc,and Chlorella-Des increased by 18.6%,23.3%,and 25.9%,respectively.However,there is a certain threshold limit for the absorption of nitrogen by Chlorella,which does not increase with the nitrogen concentration.Under low nitrogen condition when the initial nitrogen concentration was 117.6 mM,the lipid content of Chlorella pyrenoidosa at the time of harvest was the highest at 50.6%,showing an increase by 12.6%,and the lipid content of Chlorella desertis reached up to 53.2%.20.3%.The highest lipid content of Chlorella curcuma was 52.3%,at an increase of 21.4%.This shows that the oil content of the three Chlorella strains cultured under low nitrogen conditions can be promoted.(4)Cu2+ combined with nitrogen in the cultivation of desert and polar Chlorella resulted in a significant increase in the lipid concentration of Chlorella pyrenoidosa.A 16.35%increase of lipid concentration has been recorded at concentrations of 12.56 mM Cu2+ and 117.6 MM NaNO3.The concentration of the lipid content of the combination was 12.56 mM Cu2+ and 29.4 mM NaNO3,and the grease content increased by 24.14%.It was shown that low nitrogen stress conditions increase the lipid and protein content of desert and Chlorella vulgaris,respectively.Hence,these two Chlorella strains are considered to be suitable for low-cost large-scale outdoor cultivation... |
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