The role of the NADH-dependent nitrite reductase, Nir, from Escherichia coli in fermentative ammonification
The role of the NADH-dependent nitrite reductase, Nir, from Escherichia coli in fermentative ammonification
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DOI：
10.1007/s00203-018-1590-3
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发表时间：
2019-05-01
影响因子：
2.8
通讯作者：
Hargrove, Mark S.
中科院分区：
文献类型：
--
作者：
Wang, Xiaoguang;Tamiev, Denis;Hargrove, Mark S.
硝酸盐和亚硝酸盐还原对氮同化和厌氧代谢至关重要，并且了解每个参与还原酶的具体作用对于描述决定细胞对其环境的反应的生化平衡是必要的。大肠杆菌中的可溶性细胞质siroheme NADH-亚硝酸盐还原酶（Nir）是硝酸盐/亚硝酸盐同化所必需的，但也有报道可以使亚硝酸盐解毒，或进行发酵氨化以支持厌氧催化。从理论上讲，亚硝酸盐解毒对硝酸盐厌氧生长很重要，在此期间过量的亚硝酸盐将被还原为铵。Nir的发酵氨化作用对于在亚硝酸盐存在下厌氧生长期间非呼吸性ATP生产的最大化将是重要的。本文报道的实验旨在通过直接培养大肠杆菌来测试NIR在发酵氨化中的潜在作用。大肠杆菌沿着与缺乏Nir或呼吸性亚硝酸还原酶（Nrf）的突变菌株在厌氧条件下在限定培养基中同时监测氮利用和发酵代谢产物。为了关注Nir在发酵氨化中的作用，在大多数实验中使用pH控制以消除由于硝酸形成而导致的亚硝酸盐毒性。我们的研究结果表明，Nir在发酵生长过程中具有显着的益处，反映了发酵氨化而不是解毒。我们的结论是，发酵氨化由NIR允许积极有利的发酵葡萄糖甲酸和乙酸。这些结果和结论进行了讨论，在其他细菌和植物中的作用。
Nitrate and nitrite reduction are of paramount importance for nitrogen assimilation and anaerobic metabolism, and understanding the specific roles of each participating reductase is necessary to describe the biochemical balance that dictates cellular responses to their environments. The soluble, cytoplasmic siroheme NADH-nitrite reductase (Nir) in Escherichia coli is necessary for nitrate/nitrite assimilation but has also been reported to either detoxify nitrite, or to carry out fermentative ammonification in support of anaerobic catabolism. Theoretically, nitrite detoxification would be important for anaerobic growth on nitrate, during which excess nitrite would be reduced to ammonium. Fermentative ammonification by Nir would be important for maximization of non-respiratory ATP production during anaerobic growth in the presence of nitrite. Experiments reported here were designed to test the potential role of Nir in fermentative ammonification directly by growing E. coli along with mutant strains lacking Nir or the respiratory nitrite reductase (Nrf) under anaerobic conditions in defined media while monitoring nitrogen utilization and fermentation metabolites. To focus on the role of Nir in fermentative ammonification, pH control was used in most experiments to eliminate nitrite toxicity due to nitric acid formation. Our results demonstrate that Nir confers a significant benefit during fermentative growth that reflects fermentative ammonification rather than detoxification. We conclude that fermentative ammonification by Nir allows for the energetically favorable fermentation of glucose to formate and acetate. These results and conclusions are discussed in light of the roles of Nir in other bacteria and in plants.