Optimization And Scale-up Of Heterotrophic Cultivation And Outdoor Photoinduction Of Galdieria Sulphuraria 074G Cultivation For Efficient Production Of Phycocyanin

Phycocyanin is a natural blue-colored biliprotein,and has greater commercial application value in the medical and health care field.Compared with the Spirulina,Galdieria sulphuraria has higher phycocyanin yield,and its phycocyanin has obvious advantages in high temperature resistance and photosensitivity.Therefore,G.sulphuraria has attracted widespread attention.In-depth study of the high-efficiency and large-scale production of phycocyanin by G.sulphuraria 074G has gradually become of greater and greater practical significance.In this study,G.sulphuraria 074G was taken as the research object.Based on the "Sequential Heterotrophy-Dilution-Photoinduction"(SHDP)technology studied previously by our laboratory,we have further optimized the heterotrophic culture process and increased the yield of G.sulphuraria 074G cells after photoinduction.Furthermore,the outdoor photoinduction was optimized according to the local climate conditions.Finally,the yield of phycocyanin was improved,meanwhile heterotrophic cultivation and outdoor photoinduction were scaled up successfully.In short,these results have greatly promoted the industrialization of phycocyanin production by G.sulphuraria 074G.The main conclusions are as follows:(1)In the optimization of heterotrophic cultivation,the effects of loading volume,seed age,initial carbon-to-nitrogen ratio,organic nitrogen source and other factors on the heterotrophic culture of G.sulphuraria 074G were optimized by flask experiment;the pH between 0.98?1.43 was determined to be suitable for logarithmic growth of G.sulphuraria 074G.It is confirmed that the removal of halogen elements has little effect on the culture,but the salinity and dissolved oxygen have a great effect on the growth of G.sulphuraria 074G.After the above optimization,the final biomass increased by 26%.(2)In the study on the scaling up of heterotrophic cultivation,the heterotrophic culture of G.sulphuraria 074G in the 50L fermenter was optimized.And the cell density reached 154 g/L at 697 h,exceeding the highest density reported in the literature.Then the heterotrophic culture of G.sulphuraria 074G was enlarged on a 500 L fermentation tank.And the cell density reached 54.9 g/L at 398 h,which was 19.35%higher than that in the 50L tank at the same time(46 g/L at 404h).And this heterotrophic scale is the largest scale in the reported literature about the heterotrophic culture of G.sulphuraria.(3)In the study of photoinduction optimization,the optimal time point for heterotrophic cells to photoinduction was determined at 200 h.It was determined that low-speed centrifugation will not adversely affect the subsequent photoinduction of heterotrophic cells.It is determined that the mixotrophy mode cannot achieve the accumulation of G.sulphuraria 074G biomass,and the specific growth rate of cells under photoautotrophic conditions is up to 0.39 g/L/d,which is 2.63 times that of mixotrophy conditions.It is confirmed that the photoinduction effect of heterotrophic cells will decrease after more than 12h of preservation,whether at normal or cold temperature.(4)In the study of the photoinduction scaling up,the G.sulphuraria 074G was photoinducted using an outdoor 800L horizontal tube reactor.The final cell density reached 1.84 g/L,and the phycocyanin yield was 21.26 mg/L/d,which is better than that in the outdoor 120 L runway pool conducted previously in our lab(phycocyanin yield is only 17.25 mg/L/d),suggesting the photoinduction cultivation of G.sulphuraria 074G was scaled up successfully in a 800L horizontal tube reactor.(5)A new photoinduction strategy of gradient dilution for G.sulphuraria 074G heterotrophic cells was proposed,"Sequential Heterotrophy-Photoadaptation-Photoinduction"(SHPP)namely:first diluting the heterotrophic cells for the first time,and then perform photoadaptation.After the cells were switched to photoautotrophic mode,the cell was again diluted by half.The cell growth and phycocyanin yield of the diluted experimental group were 2.16 times and 1.38 times of those in the initial inoculation density experimental group,respectively.