Study On The Mechanism Of Tolerance,Absorption And Metabolism Of Spirulina To Arsenic

Arthrospira（Spirulina）is a kind of microalgae and is widely used due to its rich nutrition and high value.Spirulina Cultivation Park in Inner Mongolia is located in the high arsenic area of groundwater.The accumulation of heavy metals in Spirulina allows arsenic to enter the food chain,thus posing a potential health hazard.In this study,Arthrospira platensis XJ007 was used as the experimental material to study the physiological response,absorption and metabolism of As（Ⅲ）with different concentrations in Arthrospira.The tolerance,detoxification and metabolism mechanism of Arthrospira to As（Ⅲ）were investigated preliminarily at the level of biochemical and cellular metabolism.The results are as follows:1.The growth of A.platensis XJ007 cells with an initial OD₅₆₀=0.2 were treated with gradient concentrations of 0,0.5,2,10,20,50,80,100 mg/L As（Ⅲ）.Lower As（Ⅲ）concentrations have almost no effect on the entire growth cycle of Arthrospira;while higher As（Ⅲ）concentrations significantly inhibit the normal growth of the delayed growth phase of A.platensis,and even cause the death of initial algal cells,thereby reducing the initial growth rate,prolonging the growth phase,and eventually leading to a decrease in biomass.When Arthrospira cells enter the exponential phase,the toxic effect of arsenic on Arthrospira gradually decreases.The half inhibitory concentrations(IC₅₀)of As（Ⅲ）to A.platensis at 48h and 336h are 13.43 mg/L and 35.73 mg/L,respectively.2.The effects of As（Ⅲ）on the protein,photosynthetic pigment and polysaccharide content of A.platensis XJ007 in the exponential phase were observed.In the whole,lower As（Ⅲ）concentrations can increase the contents of total protein,chlorophyll a and polysaccharide of A.platensis,indicating that Arthrospira may resist lower dose of As（Ⅲ）by facilitating the synthesis of active compounds.Higher As（Ⅲ）concentrations can decrease the content of photosynthetic pigment,but have no significant effect on the content of protein and polysaccharide,speculating that the synthesis and decomposition of photosynthetic pigment are more affected by arsenic,and protein and polysaccharide may enhance the tolerance of Arthrospira to arsenic.3.The effects of As（Ⅲ）stress on the photosynthetic mechanism and energy distribution of A.platensis XJ007 PSⅡ in the delayed growth phase were demonstrated.The fluorescence parameters of PSⅡ show no significant change with As（Ⅲ）≤10 mg/L,signifying that lower concentrations of arsenic have no significant effect on the overall photochemical reaction of PSⅡ in the delayed growth phase.When As（Ⅲ）concentrations are higher than 20 mg/L,the values of Fv/Fm,PIabs,RC/CS and chlorophyll fluorescence yield all decrease obviously,indicating that photosynthesis and the activity of the PSⅡ reaction center are subjected to photoinhibition significantly.With the increase of As（Ⅲ）concentration,the values of Vj and Sm increase and decrease respectively,which manifests that large dose of arsenic cause severe damage to the electron transporter on the PSⅡ receptor side in Arthrospira,limit the electron transfer from Q_A to other receptors.The value of Wk gradually decreases with As（Ⅲ）concentration increasing,indicating that the damage of arsenic to PSⅡ receptor side is much greater than that of donor side in Arthrospira.When treated with higher As（Ⅲ）concentrations than 30 mg/L,the energy in the PSⅡ reaction center used to reduce the acceptor Q_A,transfer electron and generate fluorescence decrease obviously,while the heat dissipated energy increase significantly,thereby maintaining the energy balance in the algal cells.4.The effects of As（Ⅲ）stress on the antioxidant enzyme activity and membrane lipid peroxidation in the exponential A.platensis XJ007 were demonstrated.The activities of SOD and CAT increase firstly and then decrease with the increase of As（Ⅲ）concentration of a range of 0⁵0 mg/L,which indicate that Arthrospira can stimulate the activity of antioxidant enzymes in cells to weaken oxidative damage after being exposed to arsenic.With As（Ⅲ）concentration more than 20 mg/L,it is difficult to maintain the balance between the generation and removal of reactive oxygen species in Arthrospira,so that the degree of membrane lipid damage in the algal cells aggravate and the MDA content increase significantly.5.The experimental results show that A.platensis XJ007 can absorb lower concentration（2 mg/L）of As（Ⅲ）quickly and has a strong enrichment effect on higher As（Ⅲ）concentrations.The main metabolic detoxification mechanisms of arsenic in Arthrospira depend on oxidation and methylation,generating As（V）,DMA and a small amount of arsenic choline.The arsenic contents in the algal cells decrease with the prolonged stress,thus speculating that there are other arsenic metabolism pathways in Arthrospira.The results of this study can provide a scientific basis for the setting of arsenic species and content in the quality standard of Spirulina products,and also supply a data support that Spirulina may be used as a biological adsorbent to solve arsenic pollution in water.