Department of Soil Microbiology and Symbiotic Systems, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain.
Int J Mol Sci. 2022 Mar 21;23(6):3386. doi: 10.3390/ijms23063386.
Nitrous oxide (NO) is a powerful greenhouse gas that contributes to climate change. Denitrification is one of the largest sources of NO in soils. The soybean endosymbiont is a model for rhizobial denitrification studies since, in addition to fixing N, it has the ability to grow anaerobically under free-living conditions by reducing nitrate from the medium through the complete denitrification pathway. This bacterium contains a periplasmic nitrate reductase (Nap), a copper (Cu)-containing nitrite reductase (NirK), a -type nitric oxide reductase (cNor), and a Cu-dependent nitrous oxide reductase (Nos) encoded by the and genes, respectively. In this work, an integrated study of the role of Cu in denitrification has been performed. A notable reduction in , and gene expression observed under Cu limitation was correlated with a significant decrease in NirK, NorC and NosZ protein levels and activities. Meanwhile, expression was not affected by Cu, but a remarkable depletion in Nap activity was found, presumably due to an inhibitory effect of nitrite accumulated under Cu-limiting conditions. Interestingly, a post-transcriptional regulation by increasing Nap and NirK activities, as well as NorC and NosZ protein levels, was observed in response to high Cu. Our results demonstrate, for the first time, the role of Cu in transcriptional and post-transcriptional control of denitrification. Thus, this study will contribute by proposing useful strategies for reducing NO emissions from agricultural soils.
一氧化二氮（NO）是一种强大的温室气体，会导致气候变化。反硝化作用是土壤中 NO 最大的来源之一。大豆共生体是根瘤菌反硝化研究的模式生物，因为除了固定氮之外，它还有在自由生活条件下通过还原培养基中的硝酸盐通过完全反硝化途径进行厌氧生长的能力。该细菌含有周质硝酸盐还原酶（Nap）、含铜（Cu）的亚硝酸盐还原酶（NirK）、a 型一氧化氮还原酶（cNor）和由 和 基因分别编码的 Cu 依赖性一氧化二氮还原酶（Nos）。在这项工作中，对 Cu 在 反硝化中的作用进行了综合研究。在 Cu 限制下观察到的 、 和 基因表达显著减少与 NirK、NorC 和 NosZ 蛋白水平和活性的显著下降相关。同时，Cu 对 表达没有影响，但发现 Nap 活性明显耗尽，推测是由于 Cu 限制条件下积累的亚硝酸盐的抑制作用。有趣的是，观察到在高 Cu 下存在通过增加 Nap 和 NirK 活性以及 NorC 和 NosZ 蛋白水平的转录后调节。我们的研究结果首次证明了 Cu 在 反硝化的转录和转录后控制中的作用。因此，这项研究将通过提出减少农业土壤中 NO 排放的有用策略做出贡献。
