In Dunaliella tertiolecta, a microalga renowned for its extraordinary tolerance to high salinity levels up to 4.5 M NaCl, the mechanisms underlying its stress response have largely remained a mystery. In a groundbreaking discovery, this study identifies a choline dehydrogenase enzyme, termed DtCHDH, capable of converting choline to betaine aldehyde. Remarkably, this is the first identification of such an enzyme not just in D. tertiolecta but across the entire Chlorophyta. A 3D model of DtCHDH was constructed, and molecular docking with choline was performed, revealing a potential binding site for the substrate. The enzyme was heterologously expressed in E. coli Rosetta (DE3) and subsequently purified, achieving enzyme activity of 672.2 U/mg. To elucidate the role of DtCHDH in the salt tolerance of D. tertiolecta, RNAi was employed to knock down DtCHDH gene expression. The results indicated that the Ri‐12 strain exhibited compromised growth under both high and low salt conditions, along with consistent levels of DtCHDH gene expression and betaine content. Additionally, fatty acid analysis indicated that DtCHDH might also be a FAPs enzyme, catalyzing reactions with decarboxylase activity. This study not only illuminates the role of choline metabolism in D. tertiolecta's adaptation to high salinity but also identifies a novel target for enhancing the NaCl tolerance of microalgae in biotechnological applications.

中文翻译：

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胆碱脱氢酶通过甜菜碱合成促进杜氏藻的耐盐性

在杜氏盐藻微藻是一种以对高达 4.5 M NaCl 的高盐度具有非凡耐受性而闻名的微藻，但其应激反应的机制在很大程度上仍然是个谜。这项研究是一项突破性的发现，发现了一种称为 DtCHDH 的胆碱脱氢酶，能够将胆碱转化为甜菜碱醛。值得注意的是，这是首次鉴定出这种酶，不仅在特蒂奥莱克塔但遍及整个绿藻门。构建了 DtCHDH 的 3D 模型，并与胆碱进行分子对接，揭示了底物的潜在结合位点。该酶异源表达于大肠杆菌Rosetta (DE3) 并随后纯化，酶活达到 672.2 U/mg。阐明 DtCHDH 在耐盐性中的作用特蒂奥莱克塔，RNAi被用来敲低DtCHDH基因的表达。结果表明，Ri-12 菌株在高盐和低盐条件下均表现出生长受损，并且 DtCHDH 基因表达和甜菜碱含量水平一致。此外，脂肪酸分析表明，DtCHDH 也可能是一种 FAP 酶，可催化具有脱羧酶活性的反应。这项研究不仅阐明了胆碱代谢在特蒂奥莱克塔不仅适应了高盐度，而且还确定了在生物技术应用中增强微藻耐氯化钠的新目标。