Agrobacterium fabrum C58 is a plant-associated bacterium that is able to denitrify under anoxic conditions. The cluster of denitrification genes harbored by this strain has been well characterized. It includes nir and nor operons encoding nitrite and nitric oxide reductases, respectively. However, the reductase involved in nitrate reduction has not yet been studied and little information is available on denitrification regulators in A. fabrum C58. In this study, we aimed to (i) characterize the nitrate reductase, (ii) determine its role in A. fabrum C58 fitness and root colonization and (ii) reveal the contribution of small RNA on denitrification regulation. By constructing a mutant strain defective for napA, we demonstrated that the reduction of nitrate to nitrite was catalyzed by the periplasmic nitrate reductase, NapA. We evidenced a positive role of NapA in A. fabrum C58 fitness and suggested that A. fabrum C58 is able to use components exuded by plant roots to respire anaerobically. Here, we showed that NorR small RNA increased the level of norCBQ mRNA and a decrease of NorR is correlated with a decrease in N₂O emission. Together, our results underscore the importance of understanding the denitrification pathway at the strain level in order to develop strategies to mitigate N₂O production at the microbial community level.

中文翻译：

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Fabrum C58农杆菌涉及硝酸还原酶NapA和反义RNA NorR的反硝化作用

Fabrum C58农杆菌是一种植物相关细菌，能够在缺氧条件下反硝化。该菌株具有的反硝化基因簇已被很好地表征。它包括分别编码亚硝酸盐和一氧化氮还原酶的nir和nor操纵子。然而，尚未研究与硝酸盐还原有关的还原酶，并且关于Fabric C58中反硝化调节剂的信息很少。在这项研究中，我们旨在（i）表征硝酸还原酶，（ii）确定其在A.fabrum C58适应性和根定植中的作用，以及（ii）揭示小RNA对反硝化调节的贡献。通过构建对napA有缺陷的突变菌株，我们证明了硝酸盐还原为亚硝酸盐是由周质硝酸还原酶NapA催化的。我们证明了NapA在A. fabrum C58健身中具有积极作用，并建议A. fabrum C58能够使用植物根系分泌的成分进行厌氧呼吸。在这里，我们显示了NorR小RNA增加了norCBQ mRNA的水平，而NorR的减少与N ₂ O排放的减少相关。总之，我们的结果强调了在菌株水平上了解反硝化途径的重要性，以便制定在微生物群落水平上减轻N ₂ O产生的策略。