Study On The Effects Of Light Spectrum And Zn²⁺ Concentration On The Growth And Phycocyanin Accumulation Of Spirulina

Light spectrum can be regarded as the wavelength of light,which is one of the important factors affecting photosynthesis in Spirulina and is related to the growth of Spirulina and the synthesis of active ingredients such as phycocyanin.Zinc is an essential trace element for the growth of Spirulina,and Spirulina contains zinc and other nutrients.Zinc is a vital element in living organisms and is closely related to the maintenance of normal metabolism in the organism.Currently,the high-value development and utilization of Spirulina is in a bottleneck.Therefore,the cultivation of Spirulina using suitable light spectrum and zinc ions has the potential to convert inorganic zinc to organic zinc and enhance its phycocyanin production.In this paper,the Spirulina SH（mixed algae）,Spirulina maxima Sm-5 and Spirulina platensis GY-D18-16 from the Key Laboratory of Environment and Resource Utilization,Ministry of Education,Poyang Lake were selected as the study species.We investigated the changes of growth and active ingredient content of Spirulina under zinc stress in the culture medium,explored the effects of light spectrum,Zn²⁺concentration and photoperiod on the growth and phycocyanin accumulation of different Spirulina species as well as optimized the two-stage culture strategy,which finally enhanced the phycocyanin yield and provided some reference values for the production of high value-added Spirulina products.The results of the study were as follows:（1）Using different initial zinc ion concentration stress cultures of Spirulina SH,it was shown that the biomass of SH reached a maximum of 1.72 g/L at a Zn²⁺concentration of 4 mg/L.This Zn²⁺concentration effectively enhanced the content of active ingredients such as phycocyanin.This indicates that the moderate concentration of Zn²⁺stress promoted the growth of Spirulina and the accumulation of bioactive substances.The growth of the algae was inhibited when the Zn²⁺concentration was≥12 mg/L;the highest zinc accumulation was 4829 mg/kg when the Zn²⁺concentration was 20 mg/L.The study indicated that Spirulina has the ability to absorb certain concentration of zinc.（2）Under five different light cultures,the biomass accumulation of Spirulina was ranked from high to low:red light>orange light>white light>green light>blue light,and the highest phycocyanin content was reached under blue light.It showed that red light effectively promoted the growth of algae and blue light could enhance the content of phycocyanin.The results of incubation under red and blue light showed that 4 mg/L zinc ion concentration and 24/0-h（light/dark-h）photoperiod were the best conditions for Spirulina biomass and phycocyanin accumulation.（3）Combination of red and blue light and optimized culture conditions were used to cultivate Spirulina using a two-stage method to enhance phycocyanin yield.Under strategy 1（5 days of red light culture in the first stage and 3 days of blue light culture in the second stage）,SH,Sm-5 and GY-D18-16 accumulated high biomass of 1.65,1.86 and 1.57 g/L,respectively,and the highest phycocyanin content of 26.31%,22.53%and 23.64%,respectively.Under strategy 2（5 days of blue light culture at the beginning and 3 days of red light culture at the end）,Spirulina had higher phycocyanin content at the end of blue light culture,but the change to red light culture led to a significant decrease in phycocyanin content and much lower biomass than strategy 1,resulting in lower phycocyanin production under strategy 2 than strategy 1.Under strategy 1 culture conditions,SH,Sm-5 and GY-D18-16 had the highest phycocyanin yields,which were52.59,57.12 and 44.15 mg/L/d,respectively.The results indicated that the two-stage culture of strategy 1 finally enhanced the phycocyanin yield of Spirulina.