Background Nannochloropsis gaditana is a photosynthetic unicellular microalgae considered one of the most interesting marine algae to produce biofuels and food additive due to its rapid growth rate and high lipid accumulation. Although microalgae are attractive platforms for solar energy bioconversion, the overall efficiency of photosynthesis is reduced due to the steep light gradient in photobioreactors. Moreover, accumulation of lipids in microalgae for biofuels production is usually induced in a two-phase cultivation process by nutrient starvation, with additional time and costs associated. In this work, a biotechnological approach was directed for the isolation of strains with improved light penetration in photobioreactor combined with increased lipids productivity. Results Mutants of Nannochloropsis gaditana were obtained by chemical mutagenesis and screened for having both a reduced chlorophyll content per cell and increased affinity for Nile red, a fluorescent dye which binds to cellular lipid fraction. Accordingly, one mutant, called e8, was selected and characterized for having a 30% reduction of chlorophyll content per cell and an almost 80% increase of lipid productivity compared to WT in nutrient-replete conditions, with C16:0 and C18:0 fatty acids being more than doubled in the mutant. Whole-genome sequencing revealed mutations in 234 genes in e8 mutant among which there is a non-conservative mutation in the dgd1 synthase gene. This gene encodes for an enzyme involved in the biosynthesis of DGDG, one of the major lipids found in the thylakoid membrane and it is thus involved in chloroplast biogenesis. Lipid biosynthesis is strongly influenced by light availability in several microalgae species, including Nannochloropsis gaditana: reduced chlorophyll content per cell and more homogenous irradiance in photobioreactor is at the base for the increased lipid productivity observed in the e8 mutant. Conclusions The results herein obtained presents a promising strategy to produce algal biomass enriched in lipid fraction to be used for biofuel and biodiesel production in a single cultivation process, without the additional complexity of the nutrient starvation phase. Genome sequencing and identification of the mutations introduced in e8 mutant suggest possible genes responsible for the observed phenotypes, identifying putative target for future complementation and biotechnological application.

中文翻译：

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通过选择淡绿色突变体，在氮充足的条件下提高了 Nannochloropsis gaditana 的脂质生产力。

背景 Nannochloropsis gaditana 是一种光合单细胞微藻，由于其快速生长和高脂质积累，被认为是生产生物燃料和食品添加剂的最有趣的海藻之一。尽管微藻是太阳能生物转化的有吸引力的平台，但由于光生物反应器中陡峭的光梯度，光合作用的整体效率会降低。此外，用于生物燃料生产的微藻中脂质的积累通常是在营养缺乏的两阶段培养过程中引起的，需要额外的时间和成本。在这项工作中，一种生物技术方法旨在分离在光生物反应器中具有改善的光穿透性并增加脂质生产力的菌株。结果 Nannochloropsis gaditana 的突变体通过化学诱变获得，并筛选出每个细胞的叶绿素含量降低和对尼罗红的亲和力增加，尼罗红是一种与细胞脂质部分结合的荧光染料。因此，选择了一种称为 e8 的突变体，其特征在于在营养充足的条件下，与 WT 相比，每个细胞的叶绿素含量减少 30%，脂质生产力增加近 80%，具有 C16:0 和 C18:0 脂肪酸在突变体中增加了一倍以上。全基因组测序发现e8突变体中有234个基因发生突变，其中dgd1合酶基因有一个非保守突变。该基因编码一种参与 DGDG 生物合成的酶，类囊体膜中发现的主要脂质之一，因此它参与叶绿体的生物发生。脂质生物合成受到几种微藻物种的光利用率的强烈影响，包括 Nannochloropsis gaditana：每个细胞的叶绿素含量降低和光生物反应器中更均匀的辐照度是在 e8 突变体中观察到的脂质生产力增加的基础。结论 本文获得的结果提出了一种很有前景的策略，可以在单一培养过程中生产富含脂质部分的藻类生物质，用于生物燃料和生物柴油生产，而不会增加营养缺乏阶段的额外复杂性。e8 突变体中引入的突变的基因组测序和鉴定表明可能导致观察到的表型的基因，