Biotransformation of waste oil into value-added nutraceuticals provides a sustainable strategy. Thraustochytrids are heterotrophic marine protists and promising producers of omega (ω) fatty acids. Although the metabolic routes for the assimilation of hydrophilic carbon substrates such as glucose are known for these microbes, the mechanisms employed for the conversion of hydrophobic substrates are not well established. Here, thraustochytrid Schizochytrium limacinum SR21 was investigated for its ability to convert oils (commercial oils with varying fatty acid composition and waste cooking oil) into ω-3 fatty acid; docosahexaenoic acid (DHA). Within 72 h SR21 consumed ~ 90% of the oils resulting in enhanced biomass (7.5 g L− 1) which was 2-fold higher as compared to glucose. Statistical analysis highlights C16 fatty acids as important precursors of DHA biosynthesis. Transcriptomic data indicated the upregulation of multiple lipases, predicted to possess signal peptides for secretory, membrane-anchored and cytoplasmic localization. Additionally, transcripts encoding for mitochondrial and peroxisomal β-oxidation along with acyl-carnitine transporters were abundant for oil substrates that allowed complete degradation of fatty acids to acetyl CoA. Further, low levels of oxidative biomarkers (H2O2, malondialdehyde) and antioxidants were determined for hydrophobic substrates, suggesting that SR21 efficiently mitigates the metabolic load and diverts the acetyl CoA towards energy generation and DHA accumulation. The findings of this study contribute to uncovering the route of assimilation of oil substrates by SR21. The thraustochytrid employs an intricate crosstalk among the extracellular and intracellular molecular machinery favoring energy generation. The conversion of hydrophobic substrates to DHA can be further improved using synthetic biology tools, thereby providing a unique platform for the sustainable recycling of waste oil substrates.

中文翻译：

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转录组学有助于揭示裂殖壶菌在疏水底物生物转化为二十二碳六烯酸过程中的代谢变化和分子机制

将废油生物转化为增值营养保健品提供了可持续的战略。破囊壶菌是异养海洋原生生物，是有前途的 omega (ω) 脂肪酸生产者。尽管这些微生物同化亲水性碳底物（例如葡萄糖）的代谢途径是已知的，但用于转化疏水性底物的机制尚未明确。在此，研究了破囊壶菌 Schizochytrium limacinum SR21 将油（具有不同脂肪酸组成的商业油和废弃食用油）转化为 ω-3 脂肪酸的能力；二十二碳六烯酸（DHA）。在 72 小时内，SR21 消耗了约 90% 的油，导致生物量增加 (7.5 g L−1)，比葡萄糖高 2 倍。统计分析强调 C16 脂肪酸是 DHA 生物合成的重要前体。转录组数据表明多种脂肪酶的上调，预计这些脂肪酶具有用于分泌、膜锚定和细胞质定位的信号肽。此外，编码线粒体和过氧化物酶体β-氧化的转录物以及酰基肉碱转运蛋白对于油底物来说是丰富的，使得脂肪酸完全降解为乙酰辅酶A。此外，疏水底物的氧化生物标志物（H2O2、丙二醛）和抗氧化剂水平较低，表明 SR21 有效减轻代谢负荷，并将乙酰 CoA 转向能量产生和 DHA 积累。这项研究的结果有助于揭示 SR21 同化油底物的途径。破囊壶菌利用细胞外和细胞内分子机制之间复杂的串扰来产生能量。使用合成生物学工具可以进一步提高疏水底物向 DHA 的转化，从而为废油底物的可持续回收提供独特的平台。