Lipid production in Dunaliella bardawil under autotrophic, heterotrophic and mixotrophic conditions

ABSTRACT Many microalgae are rich in lipid. Due to their low growth rates in the autotrophic culture, the best alternative is to cultivate cells under different conditions such as heterotrophic or mixotrophic, which results in the highest yield of biomass and lipid in the shortest duration. In this study, Dunaliela bardawil (UTEX 2538) green microalgae was cultivated under different culture conditions, autotrophic, heterotrophic and mixotrophic, and effects on cell concentration, lipid production and reactive oxygen species (ROS), total chlorophyll and beta-carotene concentrations were investigated. Due to very low cellular growth, this alga is not recommended for heterotrophic culture. In terms of mixotrophic conditions containing different concentrations of glucose or acetate, the highest cell growth and lipid production in 60mM glucose was similar to the control (autotrophic condition), while the concentrations of chlorophyll and beta-carotene decreased. However, at all concentrations of acetate, a slight increase in cell growth was achieved, while the lipid content decreased. Additionally, the concentrations of chlorophyll and beta-carotene increased. A positive correlation was observed between beta-carotene biosynthesis and lipid production, as well as levels of reactive species of oxygen and lipid production in the presence of glucose and acetate. This study showed that for D. bardawil the mixotrophic culture with 60mM glucose was the most suitable type of culture for increasing lipid content and cell growth rates in less time (one week).

摘要 许多微藻富含脂质。由于微藻在自养培养条件下生长速率较低，因此异养或混养等不同培养方式是最佳替代方案，可在最短周期内获得最高的生物量与脂质产量。本研究以巴氏杜氏藻（Dunaliela bardawil，UTEX 2538）为研究对象，设置自养、异养、混养三种不同培养条件，考察其对细胞浓度、脂质产量、活性氧（reactive oxygen species, ROS）、总叶绿素及β-胡萝卜素浓度的影响。由于该藻的细胞生长速率极低，因此不建议采用异养培养方式。在设置不同浓度葡萄糖或乙酸盐的混养条件中，添加60mM葡萄糖组的细胞生长与脂质产量最高，与对照组（自养培养条件）相当，但叶绿素与β-胡萝卜素浓度有所下降。而所有乙酸盐浓度梯度下，细胞生长均出现小幅提升，但脂质含量有所降低，与此同时，叶绿素与β-胡萝卜素浓度则有所升高。研究还发现，在葡萄糖与乙酸盐培养条件下，β-胡萝卜素生物合成与脂质产量之间，以及活性氧水平与脂质产量之间均存在正相关关系。本研究表明，对于巴氏杜氏藻而言，添加60mM葡萄糖的混养培养方式是最适宜的培养方案，可在更短周期（一周）内提升脂质含量与细胞生长速率。