Isochrysis’s Recycling Culture,Harvest And Cryopreservation

With the rapid development of aquaculture industry,the demand for aquaculture bait is increasing year by year.As a high-quality seedling bait,Isochrysis zhanjiangensis is very importance to the aquaculture industry.However,limited by the development and cost of recycling culture,harvest and cryopreservation technology of Isochrysis zhanjiangensis,today,there are still great challenges in the large-scale intensive production and supply.Therefore,this paper explores the techniques of recycling culture,harvest and cryopreservation of Isochrysis zhanjiangensis.Isochrysis zhanjiangensis 30005 did not result in normal growth in the recycling medium with only trace elements supplemented but not treated.However through 5 g/L activated carbon and 0.22μm treatment can successfully realize the four recycling culture of Isochrysis zhanjiangensis.There is no significant difference in the biomass and growth of algae cell in the recycling medium compared with the fresh medium.After repeated recycling culture,the biomass content of Isochrysis zhanjiangensis decreased to a certain extent.However,the treated recycling medium reduced the decline of biomass significantly,and the total organic carbon content of the recycling medium treated with activated carbon decreased significantly.Combining the membrane treatment with the polyaluminium chloride flocculation harvest,Isochrysis zhanjiangensis 30005 did result in normal growth in the recycling medium,and the harvest efficiency is close to 90%.In the study of Isochrysis zhanjiangensis’s flocculation harvest,Isochrysis zhanjiangensis1750 and Isochrysis zhanjiangensis 30005 were used in experiment.Firstly,by adjusting the concentration of metal ions in the culture medium,it is concluded that Mg²⁺is the main ion in alkali flocculation.When c(Mg²⁺)=39 mmol/L,the harvest efficiency of the two kinds of Isochrysis zhanjiangensis reached more than 90%.The use of polyaluminium chloride as flocculant has achieved good results.When the concentration of polyaluminium chloride is 1g/L,the harvest efficiency of the two kinds of Isochrysis zhanjiangensis is more than 90%.Tween 80 and chitosan can achieve 80%recovery efficiency of Isochrysis zhanjiangensis 1750.Chitosan,sodium alginate,cationic starch,tween 80 and F68 can achieve more than 80%recovery efficiency of Isochrysis zhanjiangensis 30005,and the F68 is the highest up to 90%.Last,explored the p H influence of alkali flocculation Isochrysis zhanjiangensis 1750 and Isochrysis zhanjiangensis 30005.The results show that the recovery efficiency of Isochrysis zhanjiangensis 1750 is more than 90%when the p H value is 10,11.5 and above,and Isochrysis zhanjiangensis 30005 is more than 90%when the p H value is 11.5 and above.The results of the variation trend about the the two kinds of Isochrysis zhanjiangensis sedimentation efficiency with time show that the the two kinds of Isochrysis zhanjiangensis start sedimentation when sedimentation 8 hours have passed.The biggest problem in the preservation of Isochrysis zhanjiangensis 30005 is the reduction of cells.Therefore,when the cell density is lower than 10⁷/m L,it is not suitable for preservation.Low temperature preservation at 4℃is more conducive to maintain the number of cells.Adding 0.1%VC or 0.1%VE as preservative can improve the cell activity,and also significantly improve the maintenance of the number of cells.In addition,after storage,a large number of carbohydrate were converted into lipid,but the protein content didn’t change significantly.The algal cells stored at 10⁶/ml and within 32 days can recover growth（with obvious color change）in one month.The algal cells stored at 10⁷/ml and above may need more than one month to recover and then growth.In short,this study explored the way to realize the recycling culture of Isochrysis zhanjiangensis and harvest Isochrysis zhanjiangensis efficiently,and verified that the combination of recycling culture and flocculation sedimentation can be realized.In addition,explored the conditions to better realize the long-term preservation of algal cells and discussed the possibility of recovery culture of preserved algal cells.The successful realization of recycling culture and high-efficiency harvest can reduce the cost of the Isochrysis zhanjiangensis’s commercial production.The exploration of preservation conditions will laid a certain foundation for the stable application of Isochrysis zhanjiangensis.