Bradyrhizobia are abundant soil bacteria, which can form nitrogen-fixing symbioses with leguminous plants, including important crops such as soybean, cowpea and peanut. Many bradyrhizobia can denitrify, but studies have hitherto focused on a few model organisms. We screened 39 diverse Bradyrhizobium strains, isolated from legume nodules. Half of them were unable to reduce N2 O, making them sources of this greenhouse gas. Most others could denitrify NO3 - to N2 . Time-resolved gas kinetics and transcription analyses during transition to anaerobic respiration revealed a common regulation of nirK, norCB and nosZ (encoding NO2 - , NO and N2 O reductases), and differing regulation of napAB (encoding periplasmic NO3 - reductase). A prominent feature in all N2 -producing strains was a virtually complete hampering of NO3 - reduction in the presence of N2 O. In-depth analyses suggest that this was due to a competition between electron transport pathways, strongly favouring N2 O over NO3 - reduction. In a natural context, bacteria with this feature would preferentially reduce available N2 O, produced by themselves or other soil bacteria, making them powerful sinks for this greenhouse gas. One way to augment such populations in agricultural soils is to develop inoculants for legume crops with dual capabilities of efficient N2 -fixation and efficient N2 O reduction.

中文翻译：

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有效减少结节性根瘤菌的各种分离物中N 2 O还原的常见机制。

缓生根瘤菌是丰富的土壤细菌，可与豆科植物（包括重要的农作物，如大豆，cow豆和花生）形成固氮共生酶。许多缓生性根瘤菌可以反硝化，但是迄今为止，研究集中在少数模型生物上。我们筛选了从豆类结节中分离出来的39种不同的Bradyrhizobium菌株。他们中有一半无法还原N2 O，因此成为这种温室气体的来源。其他大多数可以将NO3-反硝化为N2。过渡到厌氧呼吸过程中的时间分辨气体动力学和转录分析显示，nirK，norCB和nosZ（编码NO2-，NO和N2O还原酶）具有共同的调节作用，而napAB（编码周质NO3-还原酶）的调节也不同。在所有产生N2的菌株中，一个突出的特征是在存在N2 O的情况下几乎完全阻碍了NO3-的还原。深入分析表明，这是由于电子传输途径之间的竞争，与N03-还原相比，N2 O更具优势。在自然环境中，具有此功能的细菌会优先减少自身或其他土壤细菌产生的可利用的N2 O，使其成为这种温室气体的有力吸收者。增加农业土壤中此类种群的一种方法是开发具有有效固氮和有效减少N2O双重功能的豆类作物接种剂。具有此功能的细菌会优先减少自身或其他土壤细菌产生的可利用的N2 O，从而使其成为该温室气体的强大汇。增加农业土壤中此类种群的一种方法是开发具有有效固氮和有效减少N2O双重功能的豆类作物接种剂。具有此功能的细菌会优先减少自身或其他土壤细菌产生的可利用的N2 O，从而使其成为该温室气体的强大汇。增加农业土壤中此类种群的一种方法是开发具有有效固氮和有效减少N2O双重功能的豆类作物接种剂。