The recently proposed partial denitrification (PD), terminating nitrate reduction to nitrite, has been regarded as a promising alternative to nitrite supplying for anammox bacteria. The most important aspect of the PD process for engineering application is the stable and continuous supply of nitrite. However, the activity of nitrate reductase is often higher than that of nitrite reductase (NIR), making it difficult to accumulate nitrite during the denitrification process. Herein, a strategy for achieving efficient and stable partial denitrification using the biosafe additive dimethyl sulfoxide (DMSO) was constructed, and the mechanism of DMSO inhibiting NIR was analyzed. DMSO addition reduced the expression of NIR gene, and 1% DMSO addition can significantly inhibit NIR enzyme activity to achieve a stable PD process. When the DMSO concentration increased to 3.5%, the NIR enzyme activity was almost inhibited with the enzyme activity of only 0.95 mg nitrite/min. However, the addition of DMSO has almost no inhibitory effect on the nitrate reductase (NAR) enzyme. The affinity constant of DMSO with the NAR enzyme is −2.4 kcal/mol, while the affinity constant of DMSO with the NIR enzyme is as high as −3.1 kcal/mol. DMSO shows a higher affinity for NIR. Moreover, DMSO and nitrite occupy the same catalytic cavity in the NIR enzyme, which is the fundamental reason why DMSO selectively inhibits the NIR enzyme. This study provides a new idea for realizing efficient and stable partial denitrification function.

中文翻译：

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通过使用 Biosafe 非质子溶剂 DMSO 选择性抑制亚硝酸盐还原酶实现稳定的部分反式反应


最近提出的部分反硝化 （PD） 终止硝酸盐还原为亚硝酸盐，被认为是为厌氧氨氧化细菌供应亚硝酸盐的有前途的替代方案。用于工程应用的 PD 工艺最重要的方面是亚硝酸盐的稳定和持续供应。然而，硝酸盐还原酶的活性通常高于亚硝酸盐还原酶 （NIR），因此在反硝化过程中难以积累亚硝酸盐。在此，构建了使用 biosafe 添加剂二甲基亚砜 （DMSO） 实现高效稳定的部分反硝化的策略，并分析了 DMSO 抑制 NIR 的机制。DMSO 添加可降低 NIR 基因的表达，添加 1% DMSO 可显著抑制 NIR 酶活性，实现稳定的 PD 过程。当 DMSO 浓度增加到 3.5% 时，NIR 酶活性几乎受到抑制，酶活性仅为 0.95 mg 亚硝酸盐/分钟。然而，添加 DMSO 对硝酸还原酶 （NAR） 酶几乎没有抑制作用。DMSO 与 NAR 酶的亲和力常数为 −2.4 kcal/mol，而 DMSO 与 NIR 酶的亲和常数高达 −3.1 kcal/mol。DMSO 对 NIR 显示出更高的亲和力。此外，DMSO 和亚硝酸盐在 NIR 酶中占据相同的催化腔，这是 DMSO 选择性抑制 NIR 酶的根本原因。本研究为实现高效稳定的部分反硝化功能提供了新思路。