Low temperature generally restricts biological activity, slowing down electron transfer in biogeochemical cycles and causing a series of environmental problems such as nitrogen pollution. We present a strategy to boost electron transfer in microbial cell at low temperatures via stimulation with low current. It is demonstrated by establishing a constructed wetland system coupled with solar powered microbial electrolysis cell, which enhances microbial activity through external micro currents (18.9±5.5 μA) for removing nitrogen pollution in winter (average temperature from -6.6 to 4.5 °C). We investigated the efficiency of pollutants removal, microbial activity, N₂O production and its mechanisms using complexes activity detection, RT-qPCR, incubation, and ¹⁵N-¹⁸O dual-isotope labeling techniques. The activity of complexes I, II, III, and IV collectively represent the microbial electron transfer rate. Results indicated that the microcurrents increased the activity of complexes II, III and IV by 96%, 172%, and 313%, respectively. The transcription abundance of amoA genes in ammonia oxidation and nirS/K genes in denitrification by 263% and 51%, respectively. Consequently, NH₄⁺-N removal efficiency improved from 23% to 35%, and NO₃^--N removal efficiency from 21% to 31%. Moreover, microcurrents reduced N₂O emission by 44%. However, external microcurrent stimulation did not alter the microbial production pathway of N₂O as determined by the ¹⁵N-¹⁸O dual isotope labeling technique. The relative abundance of the nitrifying bacteria Nitrosomonas, Nitrosospira, and Nitrospira, as well as the denitrifying bacteria Methylotenera, significantly increased due to microcurrent stimulation. Specifically, Nitrospira exhibited the highest increase of 156%. Our findings provide a novel way to enhance N removal efficiency and simultaneously reduce N₂O emission of biological system like constructed wetlands in winter conditions.

中文翻译：

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增强电子转移，提高低温脱氮效率和减少 N2O


低温通常会限制生物活性，减慢生物地球化学循环中的电子转移，并引起氮污染等一系列环境问题。我们提出了一种策略，通过低电流刺激在低温下促进微生物细胞中的电子转移。通过建立人工湿地系统与太阳能微生物电解池相结合来证明，该系统通过外部微电流 （18.9±5.5 μA） 增强微生物活性，以去除冬季（平均温度为 -6.6 至 4.5 °C）的氮污染。我们使用复合物活性检测、RT-qPCR、孵育和 ^{15 N-18}O 双同位素标记技术研究了污染物去除效率、微生物活性、N₂O 产生及其机制。复合物 I、II、III 和 IV 的活性共同代表微生物电子转移速率。结果表明，微电流使复合物 II 、 III 和 IV 的活性分别提高了 96% 、 172% 和 313%。氨氧化中 amoA 基因的转录丰度和 nirS/K 基因在反硝化作用中的转录丰度分别为 263% 和 51%。因此，NH₄⁺-N 去除效率从 23% 提高到 35%，NO₃^--N 去除效率从 21% 提高到 31%。此外，微电流将 N₂O 排放减少了 44%。然而，外部微电流刺激并没有改变 N₂O 的微生物产生途径，正如 ^{15 N-18}O 双同位素标记技术所确定的那样。 由于微电流刺激，硝化细菌 Nitrosomonas、Nitrosospira 和 Nitrospira 以及反硝化细菌 Methylotenera 的相对丰度显着增加。具体来说，Nitrospira 的增幅最高，为 156%。我们的研究结果提供了一种提高 N 去除效率的新方法，同时减少冬季条件下人工湿地等生物系统的 N₂O 排放。