Experimental Study On The Response Of Oleaginous Tribonema Minus In Response To Nitrite Nitrogen

Tribonema.minus can absorb nitrite which exists widely in high nitrogen water and convert it into biomass resources.However,in the process of open culture,T.minus is faced with the challenges of nitrite inhibition and unicellular microalgae pollution.In this experiment,T.minus with high oil content,self-flocculation and easy harvest was selected as the research object to explore the effects of different concentrations of free and dissociated nitrite on the growth,photosynthetic activity,chloroplast protein,physical and chemical composition and fatty acid composition of T.minus.The effects of adding Na HCO₃ to improve T.minus tolerance to free nitrite,and using free nitrite to control pollution by single-celled microalgae（Chlorella.vulgaris and Tetradesmus.obliquus）during T.minus cultivation were also explored.The main contents of this research are presented below.1.The effects of free and dissociated nitrite on the growth of T.minus were studied in this experiment.The results showed that when the p H value of the culture system was 6.5,the inhibition domain of free nitrite on T.minus was 130μg/L.When the ambient light intensity was 500μmol·m^-2·s^-1 and the dissociated nitrite concentration was 164 mg/L on the 7th day,the growth inhibition rate was 41.18%compared with the control group.Compared with the mixed nitrogen source group,the biomass of the single nitrite group decreased by 18.19%.The results showed that dissociation of nitrite could inhibit T.minus under high light intensity,while the presence of nitrate would compete with T.minus for nitrite absorption and reduce the inhibition.Free nitrite hinders the synthesis of T.minus proteins and carbohydrates and promotes the synthesis of oils and fats.Dissociation of nitrite can promote the production of protein,in addition,in different culture environments,with the increase of nitrite content,fatty acids gradually transform from monounsaturated fatty acids to polyunsaturated fatty acids.2.In this experiment,we investigated the effects of free and dissociated nitrite on the dynamic accumulation of nitrite and photosynthesis in T.minus,and the control effect of free nitrite on unicellular microalgae in mixed culture mode.The results showed that when cultured in p H 6.5 with high concentration of free nitrite（130μg/L）,the value of nitrite reductase（Ni R）decreased to lower than the initial value,and the photosynthetic structure of II（PSII）,the photosystem of which the accumulation of intracellular nitrite content was 93.75μg/g,was destroyed rapidly.On the 7th day cultured under high light intensity,the biomass of 164 mg/L dissociated nitrite decreased by 21.88%compared with the control group.High concentration of dissociated nitrite increased the proportion of light reaction center closure and heat dissipation value,and the absorbed light quantum could not be normally transferred to the side of photosystem I（PSI）for carbon fixation to produce organic matter.The addition of Na HCO₃ as carbon source could significantly increase the activity of Ni R,reduce the content of intracellular nitrite in T.minus,and improve the tolerance of T.minus to free nitrite.the value of Fm/Fv increased by 8%and 10%compared with the group without carbon source.In the mixed culture of T.minus and T.obliquus（1:1）,70μg/L and 100μg/L free nitrite could well inhibit the growth of T.obliquus and achieve the purpose of control.Different inoculation ratios were used to simulate the different pollution degrees in the process of T.minus culture in mixed culture.After the treatment of 100μg/L free nitrite,it had a good control effect on different pollution degrees of T.obliquus,and showed a good control effect on C.vulgaris only in the initial stage of pollution（1:20）,but not ideal in the middle and later stage of pollution（1:10,1:5）.On the fifth day of culture,the biomass of T.minus was only 2.2times and 1.4times of that of C.vulgaris.3.The purpose of this study was to investigate the effects of free and dissociated nitrite on T.minus light energy conversion and chloroplast protein.OJIP parameters showed that the J phase value of 130μg/L free nitrite treatment group was significantly lower than that of other treatment groups on the first day,and the characteristic point disappeared on the third day.It is suggested that high concentration of free nitrite can accelerate the reduction of primary electron receptor（QA）by T.minus in a short time and increase the absorption of energy in the center of reflection,so as to maintain the energy balance.In the later stage,the photoelectron capture and absorption ratio decreased continuously,which inhibited the plastid quinone library（PQ）and PSI reaction center,so that the photosynthetic electron transport chain could not work properly.The differences of T.minus protein expression under free nitrite stress were mainly concentrated in photosynthetic reaction center,energy production and membrane function.Under high light intensity,the inhibitory effect of dissociated nitrite on T.minus was relatively limited,and OJIP parameters showed that all treatment groups tended to balance on the 3rd day after dissociation nitrite treatment of 164mg/L under high light intensity,indicating that T.minus carried out active photoremediation under strong light.The stress of T.minus protein expression showed the functions of nitrogen assimilation,photosynthetic activity and fatty acid synthesis.The results showed that under high light intensity,the photosynthetic system of T.minus chloroplast was inhibited,the metabolism of nitride was abnormal,and the function of photosynthetic transport chain and protein synthesis were inhibited.The addition of Na HCO₃ promoted the growth and metabolism of T.minus.OJIP parameters showed that the photoelectrons accumulated by PSII in 130μg/L free nitrite treatment group could be quickly transferred to the PSI side for carbon fixation,alleviating the inhibition of free nitrite to some extent.The expression of differential protein in the treated group was higher than that in the untreated group,especially in terms of cell composition and molecular function.The specific manifestations are photosynthesis-related and up-regulation of energy metabolism system proteins.