The soybean symbiont Bradyrhizobium diazoefficiens grows anaerobically in the presence of nitrate using the denitrification pathway, which involves the nap, nir, nor, and nos genes. We previously showed that NasT acts as a transcription antitermination regulator for nap and nos gene expression. In the present study, we investigated the targets of NasT in B. diazoefficiens during denitrifying growth by performing transcription profiling with RNA-seq and quantitative reverse-transcription PCR. Most of the genes with altered expression in the absence of NasT were related to nitrogen metabolism, specifically several systems for branched-chain amino acid transport. The present results suggest that the reduced expression of genes involved in nitrogen acquisition leads to the induction of alternative sets of genes with similar functions. The ΔnasT mutant of B. diazoefficiens grew better than the wild type under denitrifying conditions. However, this enhanced growth was completely abolished by an additional loss of the narK or bjgb genes, which encode cytoplasmic systems for nitrite and nitric oxide detoxification, respectively. Since the expression of narK and bjgb was increased in the ΔnasT mutant, the growth of the ΔnasT mutant may be promoted by increased detoxification activity.

中文翻译：

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重氮慢生根瘤菌反硝化过程中抗终止因子NasT调控基因的鉴定

大豆共生菌 Bradyrhizobium diazoefficiens 在硝酸盐存在下使用反硝化途径厌氧生长，该途径涉及 nap、nir、nor 和 nos 基因。我们以前表明 NasT 充当小睡和 nos 基因表达的转录抗终止调节剂。在本研究中，我们通过使用 RNA-seq 和定量逆转录 PCR 进行转录分析，研究了反硝化生长过程中重氮芽孢杆菌中 NasT 的靶标。在没有 NasT 的情况下，大多数表达改变的基因与氮代谢有关，特别是几个支链氨基酸转运系统。目前的结果表明，参与氮获取的基因表达减少导致具有相似功能的替代基因组的诱导。B. diazoefficiens 的 ΔnasT 突变体在反硝化条件下比野生型生长得更好。然而，这种增强的生长被 narK 或 bjgb 基因的额外损失完全消除，这些基因分别编码亚硝酸盐和一氧化氮解毒的细胞质系统。由于 ΔnasT 突变体中 narK 和 bjgb 的表达增加，ΔnasT 突变体的生长可能通过增加的解毒活性来促进。