State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
State Key Laboratory of Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
Sci Total Environ. 2022 Jun 20;826:154173. doi: 10.1016/j.scitotenv.2022.154173. Epub 2022 Feb 28.
The direct effect of CO on denitrification has attracted great attention currently. Our previous studies have confirmed that CO inhibited heterotrophic denitrification and caused high nitrite accumulation and nitrous oxide emission. Cysteine is a widely reported bio-accelerator; however, its effect on denitrification under CO exposure remains unknown. In this paper, the effect of cysteine on heterotrophic denitrification and its mechanisms under CO exposure were explored with the model denitrifier, Paracoccus denitrificans. We observed that total nitrogen removal increased from 17.9% to 90.4% as cysteine concentration increased from 0 to 50 μM, probably due to restoration of cell growth and viability. Further study showed that cysteine reduced the inhibition of CO on denitrification due to multiple positive influences: (1) regulating glutathione metabolism to eliminate intracellular reactive nitrogen species (RNS), while reducing extracellular polymeric substances (EPS) levels and altering its composition, ultimately restoring cell membrane integrity (2) facilitating the transport and metabolism of carbon sources to increase NADH production, and (3) increasing intracellular iron and up-regulating the expression of key iron transporters genes (AfuA, AfuB, ExbB and TonB) to restore the transport and consumption of electron. This study suggests that cysteine can be added to recover heterotrophic denitrification performance after inhibition by elevated CO.
CO 对反硝化的直接影响目前引起了极大关注。我们之前的研究已经证实，CO 抑制异养反硝化作用，导致亚硝酸盐积累和氧化亚氮排放增加。半胱氨酸是一种广泛报道的生物促进剂；然而，其在 CO 暴露下对反硝化的影响尚不清楚。在本文中，以模式反硝化菌 Paracoccus denitrificans 为研究对象，探讨了半胱氨酸在 CO 暴露下对异养反硝化的影响及其作用机制。我们观察到，随着半胱氨酸浓度从 0 增加到 50 μM，总氮去除率从 17.9%增加到 90.4%，这可能是由于细胞生长和活力得到恢复。进一步的研究表明，半胱氨酸通过多种积极影响减轻了 CO 对反硝化的抑制作用：（1）调节谷胱甘肽代谢以消除细胞内活性氮物种（RNS），同时降低胞外聚合物（EPS）水平并改变其组成，最终恢复细胞膜完整性；（2）促进碳源的运输和代谢，增加 NADH 生成；（3）增加细胞内铁含量并上调关键铁转运体基因（AfuA、AfuB、ExbB 和 TonB）的表达，以恢复电子的运输和消耗。本研究表明，在 CO 升高抑制异养反硝化后，可以添加半胱氨酸来恢复其反硝化性能。
