The herbicide florasulam is widely used to control broadleaf weeds in modern agriculture. Although the general ecotoxicity of herbicides has been verified, their effects on non-target soil functional bacteria, e.g., nitrogen-fixing bacteria, remained unknown. Herein, we investigated the potential impacts of florasulam on the nitrogen-fixing model bacterium Azotobacter vinelandii and sought to understand the underlying mechanisms. The growth activity of A. vinelandii was inhibited by florasulam in a concentration-dependent pattern, and the half-lethal concentration (IC₅₀) was calculated as 8.21 mg/L. Surprisingly, the nitrogen-fixing activity and energy metabolism of A. vinelandii were stimulated by florasulam at 4–8 mg/L. Transcriptomic analyses revealed that the gene expression of nitrogen-fixing bacteria changed significantly after florasulam treatment. The genes encoding the iron nitrogenase and the key enzymes in the tricarboxylic acid cycle (TCA cycle) were significantly up-regulated. Metabolomic analyses elucidated that florasulam inhibited the folate metabolism pathways on the third and seventh days, directly impairing the DNA replication processes and consequently hindering the cell division, which led to the reduction of biotin and riboflavin levels. Notably, the up-regulation of amino acid biosynthesis, the TCA cycle, and glutathione metabolism networks likely maintained the high nitrogen fixation capacity of A. vinelandii. Therefore, florasulam enhanced nitrogen fixation and the energy metabolism in A. vinelandii through up-regulating the TCA cycle and the glutathione metabolism, although it inhibited bacterial growth.

中文翻译：

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除草剂 florasulam 对非靶标生物固氮菌 Azotobacter vinelandii 的生长抑制和活性刺激

除草剂 florasulam 在现代农业中广泛用于防治阔叶杂草。尽管除草剂的一般生态毒性已得到验证，但它们对非目标土壤功能细菌（例如固氮菌）的影响仍然未知。在此，我们研究了 florasulam 对固氮模式细菌 Azotobacter vinelandii 的潜在影响，并试图了解其潜在机制。A. vinelandii 的生长活性被 florasulam 以浓度依赖性模式抑制，半数致死浓度 （IC ₅₀ ） 计算为 8.21 mg/L。令人惊讶的是，在 4–8 mg/L 时，A. vinelandii 的固氮活性和能量代谢受到 4–8 mg/L 的刺激。转录组学分析显示，Florasulam 处理后固氮细菌的基因表达发生显着变化。编码铁固氮酶和三羧酸循环 （TCA cycle） 中关键酶的基因显著上调。代谢组学分析阐明，氟磺胺在第 3 天和第 7 天抑制叶酸代谢途径，直接损害 DNA 复制过程，从而阻碍细胞分裂，导致生物素和核黄素水平降低。值得注意的是，氨基酸生物合成、TCA 循环和谷胱甘肽代谢网络的上调可能维持了 A. vinelandii 的高固氮能力。因此，Florasulam 通过上调 TCA 循环和谷胱甘肽代谢来增强 A. vinelandii 的固氮和能量代谢，尽管它抑制了细菌生长。