The yield of microalgae biomass is the key to affect the accumulation of fatty acids. A few microalgae can assimilate organic carbon to improve biomass yield. In mixotrophic cultivation, microalgae can use organic carbon source and light energy simultaneously. The preference of the main energy source by microalgae determines the biomass yield. Auxenochlorella protothecoides is an oleaginous mixotrophic microalga that can efficiently assimilate glucose and accumulate a large amount of biomass and fatty acids. The current study focused on the effect of light on the growth and glucose assimilation of A. protothecoides. In this study, we found that the uptake and metabolism of glucose in A. protothecoides could be inhibited by light, resulting in a reduction of biomass growth and lipid accumulation. We employed comparative proteomics to study the influence of light on the regulation of glucose assimilation in A. protothecoides. Proteomics revealed that proteins involving in gene translation and photosynthesis system were up-regulated in the light, such as ribulose-phosphate 3-epimerase and phosphoribulokinase. Calvin cycle-related proteins were also up-regulated, suggesting that light may inhibit glucose metabolism by enhancing the production of glyceraldehyde-3-phosphate (G3P) in the Calvin cycle. In addition, the redox homeostasis-related proteins such as thioredoxin reductase were up-regulated in the light, indicating that light may regulate glucose uptake by changing the redox balance. Moreover, the increase of NADH levels and redox potential of the medium under illumination might inhibit the activity of the glucose transport system and subsequently reduce glucose uptake. A theoretical model of how glucose assimilation in A. protothecoides is negatively influenced by light was proposed, which will facilitate further studies on the complex mechanisms underlying the transition from autotrophy to heterotrophy for improving biomass accumulation.

中文翻译：

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光对原壳小球藻中葡萄糖同化的抑制。

微藻生物量的产量是影响脂肪酸积累的关键。一些微藻可以同化有机碳以提高生物质产量。在混合营养培养中，微藻可以同时利用有机碳源和光能。微藻对主要能源的偏好决定了生物量产量。Auxenolorella protothecoides 是一种含油混合营养微藻，可以有效地同化葡萄糖并积累大量的生物量和脂肪酸。目前的研究重点是光对原壳A. protothecoides生长和葡萄糖同化的影响。在这项研究中，我们发现光可以抑制原壳A. protothecoides对葡萄糖的吸收和代谢，从而导致生物量生长和脂质积累减少。我们采用比较蛋白质组学来研究光对原壳藻葡萄糖同化调节的影响。蛋白质组学显示，参与基因翻译和光合作用系统的蛋白质在光下表达上调，如核酮糖磷酸3-差向异构酶和磷酸核糖激酶。卡尔文循环相关蛋白也上调，表明光可能通过增强卡尔文循环中甘油醛-3-磷酸（G3P）的产生来抑制葡萄糖代谢。此外，氧化还原稳态相关蛋白如硫氧还蛋白还原酶在光下上调，表明光可能通过改变氧化还原平衡来调节葡萄糖的摄取。此外，光照下培养基中 NADH 水平和氧化还原电位的增加可能会抑制葡萄糖转运系统的活性，从而减少葡萄糖的摄取。提出了光如何对原壳A. protothecoides中的葡萄糖同化产生负面影响的理论模型，这将有助于进一步研究从自养向异养转变以提高生物量积累的复杂机制。