| Microalgae is a good raw material for the production of biodiesel because of its potential advantages of simple cell structure,high lipid content and high photosynthetic efficiency.At present,the commercial production of microalgal lipids and biofuels faces the core problem of high production costs.In order to increase lipid productivity and reduce production cost,cultivating microalgae through different nutritional conditions and cultivation methods is an effective strategy to achieve economically sustainable microalgae lipid accumulation.Previously studies confirmed that appropriate nitrogen limitation can promote the growth and lipid content of Scenedesmus acuminatus,and sulfur-replete was conducive to the growth of S.acuminatus,but the lipid productivity of algae cellswas low under sulfur-replete batch culture.This paper focuses on the core problem of efficient lipid accumulation in S.acuminatus,and mainly studies the effects of different nitrogen and sulfur nutrient conditions and cultivation modes?batch and two-step culture?on the growth and fatty acids accumulation of S.acuminatus.In this study,first,low-nitrogen and sulfur-replete single-factor batch cultivation of S.acuminatus was carried out to determine the content of biomass,pigments,lipid,protein,carbohydrates and fatty acids,and calculate the lipid productivity;combining the characteristics of growth and lipid production of S.acuminatus under low nitrogen and sulfur enrichment,low nitrogen two-step cultivation and sulfur-repleted-low nitrogen two-step cultivation were carried out respectively,and choose 4,8,and 12 days of culture to change the medium,analyze the changes of the growth,the biochemical components and the fatty acids,and obtain the most valuable cultivation strategies for S.acuminatus.The main findings are as follows:?1?Both low nitrogen and sulfur-replete batch cultures significantly increased the biomass of S.acuminatus?p<0.05?.Low nitrogen batch culture yielded maximum biomass,lipid content and productivity,which were 9.95 g/L,54.5%,0.2618 g·L-1·d-1,respectively.Sulfur-replete culture promotes pigment accumulation,and the protein content is significantly higher than that of low nitrogen culture?p<0.05?.The C16and C18 fatty acids of S.acuminatus accounted for more than 90%of the total fatty acids content.The relative content of C18:1 in the low nitrogen group could reach41%.?2?Under the two-step low nitrogen culture,the second stage starting on day 8was selected to promote the biomass and lipid accumulation of S.acuminatus.The initial nitrogen concentration in the second stage is directly proportional to the pigment content and the protein and carbohydrate content on day 20.In the 8-day replacement mode,the maximum biomass of the 2/5N1S group was 12.43 g/L,which was not significantly different the with 1/5N1S group?p>0.05?;the lipid content of the 0N1S group was the largest,60.91%;the 1/5N1S group had the highest lipid productivity of 0.3461 g·L-1·d-1,which was significantly higher than the low nitrogen batch culture?p<0.05?;the relative content of C18:1 was the largest when it was changed to the 2/5N1S group in 12 days,51.93%.?3?In the two-step sulfur-replete and low nitrogen cultivation,the biomass is higher as the second stage starts later,and the biomass is highest when the initial nitrogen concentration in the second stage is 1/5N1S.The pigment content is proportional to the initial nitrogen concentration in the second stage.The 8-day replacement lipid content and the highest lipid productivity were 43.96%and 0.2523g·L-1·d-1.In summary,compared with batch culture,the two-step culture mode can effectively improve the lipid production efficiency of S.acuminatus.Under the two-step low-nitrogen culture mode,S.acuminatus can obtain higher lipid productivity and fatty acids content.This study provides a theoretical basis for the control of microalgae nitrogen and sulfur nutrition conditions and large-scale cultivation. |
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