The Metabolic Response In Dunaliella Salina To Different Concentration Of CO₂ And Light Quality

The unicellular green alga Dunaliella salina can survive in extreme stations and accumulate ?–carotene,which is thought to be the best and most important biological source of ?-carotene.The organic substances of D.salina is derived from the photosynthesis of fixed CO₂.In this thesis,we studied the physiological metabolic response of D.salina to different concentrations of CO₂ and light quality in the following aspects.Firstly,the optimal growth salinity for D.salina strain HG01 was selected to be 75‰,and the next culture experiment was conducted based on this salinity.To study the response of D.salina to different concentration of CO₂,the growth rate,carbonic anhydrase?CA enzyme?activity and glycerol content under different concentration of CO₂ were investigated.Differential expression of proteins in D.salina exposed to different CO₂ concentrations was analyzed.Our results showed that different concentrations of CO₂ could affect the growth and photosynthesis of D.salina cells.The physiological and photosynthetic activity both increased as the CO₂ concentration elevated,while higher concentration suppressed this trend.The optimal group was 97%N2+3%CO₂ for cell growth.The photosynthetic activity of PSII increased under 0.03% to 3%CO₂ and was inhibited under 9%CO₂.The relative expression of photosynthesis proteins was consistent with this trend.The synthesis and portion of light-harvesting pigment was possibly regulated in D.salina in response to the CO₂ concentration change.Higher CO₂ concentration may induced excess cellular oxidative stress,and heat shock proteins and superoxide dismutase were up-regulated to cope with the negative factor.Secondly,the culture systems of different LED light qualities were designed to culture the D.salina strain HG01.The selected light qualities were red?R?,blue light?B?and white light?W?,and the transcriptomic analysis was performed.The results showed that among the three light qualities,red light was more conducive to the growth and accumulation of glycerol and other substances of the strain HG01 cells,while Blue light had a positive effect on the synthesis of carotenoid.Red light and blue light have a certain role in promoting the oxygen evolution of photosynthesis.The expression of psb O,psb P and some peripheral antenna protein genes related to photosynthetic and oxygen evolution in red light are up-regulated,and the expression of psb P in blue light is down-regulated,indicating that red light and blue light have different effects on photosynthetic oxygen release by increasing efficiency of light energy capture,or the regulation of different photosynthetic oxygenation-related proteins.Compared with red light and white light,the expression of psb S was downregulated under blue light,indicating that blue light had a certain effect on the photoprotective mechanism of D.salina.Therefore,different light qualities could cause changes in the expression of the light-harvesting antenna protein,photosynthetic oxygen release protein,and proteins in the electron transport chain,thereby affecting the photosynthesis of D.salina.In addition,transcriptome sequencing and sequence segmentation of Dunaliella salina with different light qualities were performed and reached a certain depth of sequencing.During the process of cluster analysis,functional annotation and differential enrichment analysis of the assembly and splicing sequences,a large amount of gene information of D.salina was obtained,which further enriched the gene pool of microalgae.In summary,the difference in CO₂ concentration and light quality can affect the growth,substances accumulation and photosynthesis pathway of D.salina HG01.The 3%CO₂ concentration is most suitable for the growth of this strain.The red light is more conductive to the growth of the algae cells and the accumulation of glycerol,starch and other substances while blue light can promote the synthesis of ?-carotene.The response CO₂ concentration and light quality of D.salina are mainly caused by the change of the proportion of photosynthetic pigments or the expression of their complex proteins,and in the expression of protein in the central protein and electron transport chain of the photosystem.In addition,high concentrations of CO₂ can induce oxidative stress on the cells,so that up-regulate the expression of antioxidants;blue light has an impact on the expression of psb S,which may affect the photoprotective mechanism of D.salina.Therefore,the results of this paper provide a certain theoretical guidance for the large-scale production of D.salina.