| Haematococcus pluvialis, a freshwater unicellular microalgae, receivedcomprehensive attention due to its great ability to accumulating large quantity ofastaxanthin in recent years. Currently, two main methods applied in large scaleproduction of astaxanthin were using open-ponds and photo-bioreactors respectively.But problems of low biomass productivity and susceptible to contamination in thesetwo cultivation systems were still difficult to be solved. In this paper, we used a newmethod named―Attached cultivation‖for the cultivation and induction ofHaematococcus pluvialis. This work investigated the optimal cultivation conditions, thenitrogen supply strategy and the difference between suspended and attached cultivationon astaxanthin induction, hoping for providing theoretical and experimental basis to theindustrilization of Haematococcus pluvialis.First, we investigated the optimal inoculation amount, light intensity, CO2andnitrogen concentration. The results showed that when the inoculation amount and lightintensity were10g m-2,100μmol·m-2s-1, the biomass producitivity achieved6.62±0.01g·m-2d-1. When light intensity was higher than100μmol·m-2s-1, astaxanthinaccumulated. The optimal concentration of CO2was0.5%which the biomassproductivity could reach6.75±0.18g·m-2d-1. Higher CO2concentration showed nopromotion effect on biomass productivity. The optimal nitrogen concentration was1.77mM which the biomass productivity reached6.85±0.09g·m-2d-1and under nitrogenfree condition, astaxanthin content has the highest value of1.45±0.03%. This resultshowed that by using attached cultivation method, nitrogen concentration lower than 1.77mM could induce the accumulation of astaxanthin.In attached cultivation, with the increase of the nitrogen amount, the biomassproductivity of Haematococcus pluvialis could reach the maximum value of7.99±0.03g·m-2d-1when nitrogen amount was3.53mmol. The maximum value ofastxanthin content of2.27±0.1%which obtained when nitrogen amount was0.177mmol. When the culture medium volume was1L, the maximum biomass productivityachieved6.84±0.17g m-2d-1. The maximum astaxanthin content and productivity of2.19±0.04%and133.22±2.17mg m-2d-1were both obtained when the culture mediumvolume was0.5L. The final nitrogen supply strategy was determined as dissolving0.15g nitrate sodium into0.5L medium and based on this strategy, we calculated thattotally volume of30L was demanded for cultivating an area of1m2of Haematococcuspluvialis by utilizing attached cultivation system.Then we compared the efficiency of astaxanthin accumulation of suspended andattached cultivation. Results showed that attached cultivation could achieve a highervalue of astaxanthin content of2.32±0.02%. But in terms of astaxanthin productivity,single layer attached cultivation system did not show a clear advantage over traditionalsuspended cultivation system. Based on these results, we determined the optimalinduction strategy was making algae cells subjected to the adverse conditions for a6-days‘period to accumulating astaxanthin when the biomass reached25g m-2.Comprehensive analysis on the above results showed that the attached cultivationsystem was not only suitable for cultivating Haematococcus pluvialis, but also have abetter performance compared to traditional suspended cultivation. In terms ofastaxanthin induction, attached cultivation can shorten induction period and improveastaxanthin content. Therefore, attached cultivation system has great potential andpractical value for the cultivation of Haematococcus pluvialis and induction ofastaxanthin. |
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