Effect Of Light Intensity On The Growth,Biochemical Components And Transcriptome Of Oocystis Borgei During Preservation

Oocystis borgei,a green algae,was isolated from high-level ponds of subtropical shrimps in the laboratory.It has significant advantages in regulating the water quality of shrimp farming.At present,China is the first country in the world to develop and industrialize O.borgei as a products.At present,how to make the microalgae ecological preparation products easy to preserve for a longtime and maintain biological activity is a key problem in the industrialization and application of O.borgei in shrimp culture.In this paper,the concentrated O.borgei?1.22�0.2�10⁷ cell/m L?were preserved at room temperature?25??for 100 days under five light intensity of 40 lx?400 lx?1500 lx?3000 lx and 5000 lx.The effects of light intensity on the growth,biochemical components during the preservation period and recovery of preserved O.borgei were studied by measuring the biomass,chlorophyll content,polysaccharide content,protein content,fluorescence intensity of lipid,survival rate,biomass and specific growth rate during recovery.At the same time,transcriptome sequencing was performed on O.borgei under different light intensities?40 lx,1500 lx and 5000 lx?,to explore the difference in expression profiles,and to analyze the molecular mechanism of O.borgei in response to light in order to study The molecular mechanism of O.borgei at room temperature provides new insights.The main research results are as follow:1.Light intensity has a significant effect on the growth,pigment content,and biochemical components of the concentrated O.borgei stored at room temperature for 100days?p<0.05?.Under low light conditions?400 lx and 40 lx?,O.borgei showed no growth or negative growth.The best growth light condition for O.borgei was normal light?1500lx?.In general,the contents of chlorophyll a,chlorophyll b and carotenoids all decreased with time,but the content of chlorophyll a,chlorophyll b and carotenoids in each group was negatively correlated with light intensity,and carotenoid/total chlorophyll increased with light intensity increased.O.borgei will adopt different strategies under different light levels to accumulate different biochemical components to cope with environmental changes.Under low light?40 lx?conditions,it accumulated a large amount of carbohydrates and proteins,while under strong light?5000 lx?conditions accumulated a large amount of lipids.2.Light intensity has a significant effect on the the survival rate of the concentrated O.borgei stored at room temperature for 100 days and the growth and pigment of the recultivation process?p<0.05?.Among them,the survival rate of concentrated O.borgei at 400 lx was significantly lower than that of other groups?p<0.05?,which was 82.56�1.72%.The survival rate of O.borgei preserved under extremely low light intensity or high light intensity is high,ranging from 87.78�1.08%?91.50�0.94%.O.borgei was recovered and cultured?7?10 days?after being stored under different light for 60 days,and its specific growth rate was positively correlated with light intensity.But if you want to achieve rapid recovery of algae species in the short term?2?3 days?,the specific growth rate of O.borgei preserved at 40 lx is significantly higher than that of other groups?p<0.05?,and then the advantage disappears.The chlorophyll content of O.borgei after 40days of storage under different light intensity will increase during the recovery culture period.3.Compared with the normal light group?1500 lx?,the genes of photosynthesis-antenna protein pathway were significantly up-regulated in the O.borgei stored under low light?40 lx?conditions.It showed that O.borgei synthesized more antenna proteins in order to capture light energy under low light conditions,and the key genes in the process of photosynthetic phosphorylation were significantly up-regulated,and a large amount of CO₂ was fixedly converted into sugar.Genes related to the structure and function of the ribosome were significantly up-regulated,indicating that under low light conditions,not only the extension of the peptide chain in the synthesis of new proteins,but also recognition and transport are promoted,and the protective effect on protein structure has also been promoted,resulting in a significant increase in protein content.The genes of peroxisomes and unsaturated fatty acid synthesis-related pathways were significantly up-regulated,indicating that the antioxidant capacity of O.borgei cells increased at this condition.The related genes in the nitrogen metabolism pathway are significantly up-regulated,indicating that the cells have a high absorption capacity for external inorganic nitrogen and organic nitrogen,and a large amount of ammonia is synthesized,which provides raw materials for the synthesis of proteins and nucleic acids.4.Compared with the normal light group?1500 lx?,stored under strong light?5000 lx?,the psb A and psb D genes encoding PS?reactive center proteins D1 and D2,and the Psb B gene encoding the light-harvesting pigment protein subunit cp47 is significantly down-regulated in the O.borgei It indicates that O.borgei.has been under strong light for a long time,PS?is inhibited,PS?reactive center protein is reduced,thus the structural stability is reduced,which led to the PSII's ability to use light reduced,and electron transfer and H⁺generation are reduced.The increased cytochrome b6/f complex can help transfer the electrons produced by PSII and increase the ring-shaped electron flow around PSI,while producing ATP under high light.Peroxisomal related genes were significantly up-regulated more than weak light,indicating that strong light stimulates the antioxidant system more than weak light,and the synthesis of related enzymes is also promoted.And the?oxidation process of fatty acids and unsaturated fatty acids is also promoted,which in turn promotes the synthesis of fatty acids and unsaturated fatty acids,and the analysis of the synthesis pathway of unsaturated fatty acids shows that the main product synthesized under strong light is DHA.Analysis of the nitrogen metabolism pathway resulted in significant upregulation of each gene,which provided raw materials for the synthesis of proteins and nucleic acids under this condition.Moreover,the related genes of formamide enzyme?EC3.5.1.49?are still significantly up-regulated than weak light,indicating that strong light is more conducive to the absorption of organic nitrogen.