| Haematococcus pluvialis and Nannochloropsis sp.are two microalgae with wide application prospect.Among them,H.pluvialis is the best source of natural astaxanthin,which has been used in cosmetics,food supplement,food additive and aquaculture.In addition,H.pluvialis contains amounts of lipid,being a promising feedstock for biofuel.Nannochloropsis is rich in lipid,especially EPA,and many kinds of carotenoid,having been applied in biofuel,pharmaceutical,food supplement,food additive and aquaculture.However,there are some problems in application of H.pluvialis and Nannochloropsis,such as low yield and high cost.These are due to the fact that the cultivation method has not been well optimized,and also the metabolic regulation mechanism is still not clear.In this study,the H.pluvialis was exposed to 20,70,150 ?mol m-2 s-1 white LED(W-20,W-70 and W-150),and 70 ?mol m-2 s-1 blue LED(B-70),respectively,with nitrogen being simultaneously depleted on day 2.From the astaxanthin measurement results,the astaxanthin content was higher under W-150 and B-70 than W-20 and W-70.B-70 obtained the highest astaxanthin content of 21.45 mg g-1 on day 8,which was 2.99,1.59 and 1.47 times of that for W-20,W-70 and W-150,respectively.In order to explain the variation of astaxanthin content,the gene expression of astaxanthin biosynthesis pathway was investigated.The expressions of psy,Icy,crtO and crtR-B were upregulated under B-70,while the psy,crtO and bkt2 expressions were upregulated under W-150.From the fatty acid examination results,the total fatty acid content was highest under W-150.Accordingly,the expressions of fata gene and five dgat genes were upregulated under W-150.The expression of dgat2a gene was upregulated for B-70,which is consistent with the astaxanthin esters content.Additionally,the total astaxanthin and fatty acid contents were significantly increased after nitrogen was depleted,and the expressions of related genes were significantly upregulated(except for ipil and ipi2).The effect of different wavelength LEDs on haematocyst germination was investigated in this study.From the results,blue LED improved the germination efficiency,and decreased the nitrogen consumption rate,compared with white and red LEDs.The astaxanthin extractability of day 5 under three LED conditions was significantly higher than day 0,and the astaxanthin extractability of blue LED was 4.0 and 6.7 folds of that for white and red LEDs.Moreover,the astaxanthin content was higher under blue LED.To explain this result,the expressions of blue light receptor gene phot and astaxanthin biosynthesis pathway genes were investigated.On day 4,the expression of phot gene under blue LED was significantly higher than that of white and red LEDs.The expressions of two important genes of astaxanthin biosynthesis pathway(psy and pds)were correlated with phot gene,being significantly upregulated by blue LED.Nitrogen is a key factor of astaxanthin biosynthesis in H.pluvialis,and PII protein is a key protein for controlling nitrogen metabolism.In this study,the H.pluvialis PII protein coding gene was cloned and identified.The full-length of HpGLB1 was 1222 bp;including 621 bp coding sequence(C.DS),103 bp 5'untranslated region(5' UTR),and 498 bp 3' untranslated region(3' UTR).The coding region of HpGLBl in genomic DNA contains 7 exons and 6 introns.The PII protein of H.pluvialis consisted of 206 amino acid.Its calculated molecular weight(Mw)was 22.4 kDa and the theoretical isoelectric point was 9.53.From the phylogenetic analysis,the H.pluvialis PII protein was grouped with the P? proteins of Chlorophyta algae(Chlamydomonas reinhardtii,Chlorella variabilis<Micromonas pusilla).The HpGLBl expression was upregulated 2.46 times When H.pluvialis cells were exposed to nitrogen starvation for 48 h,concomitant with the raise of astaxanthin content.Finally,the Nannochloropsis was exposed to 50 and 150 ?mol m-2 s-1 white,royal blue(440 nm),blue(460 nm),orange-red(630 nm),or red(660 nm)LEDs,respectively,and the biomass,fatty acid and carotenoid yields with respect to light output efficiency were investigated.The biomass and fatty acid yields were higher under high light intensity(150 lpmol m-2 s-1)LEDs than low light intensity(50 ?mol m-2 s-1)LEDs.However,the power efficiencies of biomass and fatty acid(specifically eicosapentaenoic acid)production were higher for low light intensity.Interestingly,low light intensity enhanced both of carotenoid power efficiency of carotenoid biosynthesis and yield.White LEDs of both light intensity were neither advantageous for biomass as well as fatty acid yields,nor the power efficiency of biomass,fatty acid,and carotenoid production.Noticeably,red LED resulted in the highest power efficiency of biomass and fatty acid production. |
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