Glyphosate is a commonly used herbicide with a broad action spectrum. However, at sublethal doses, glyphosate can induce plant growth, a phenomenon known as hormesis. Most glyphosate hormesis studies have been performed under microbe-free or reduced-microbial-diversity conditions; only a few were performed in open systems or agricultural fields, which include a higher diversity of soil microorganisms. Here, we investigated how microbes affect the hormesis induced by low doses of glyphosate. To this end, we used Arabidopsis thaliana and a well-characterized synthetic bacterial community of 185 strains (SynCom) that mimics the root-associated microbiome of Arabidopsis. We found that a dose of 3.6 × 10⁻⁶ g acid equivalent/liter (low dose of glyphosate, or LDG) produced an ∼14% increase in the shoot dry weight (i.e., hormesis) of uninoculated plants. Unexpectedly, in plants inoculated with the SynCom, LDG reduced shoot dry weight by ∼17%. We found that LDG enriched two Firmicutes and two Burkholderia strains in the roots. These specific strains are known to act as root growth inhibitors (RGI) in monoassociation assays. We tested the link between RGI and shoot dry weight reduction in LDG by assembling a new synthetic community lacking RGI strains. Dropping RGI strains out of the community restored growth induction by LDG. Finally, we showed that individual RGI strains from a few specific phyla were sufficient to switch the response to LDG from growth promotion to growth inhibition. Our results indicate that glyphosate hormesis was completely dependent on the root microbiome composition, specifically on the presence of root growth inhibitor strains.

中文翻译：

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根部微生物组调节低剂量草甘膦诱导的植物生长促进。


草甘膦是一种常用的除草剂，具有广泛的作用谱。然而，在亚致死剂量下，草甘膦可以诱导植物生长，这种现象称为毒物兴奋效应。大多数草甘膦兴奋作用研究都是在无微生物或微生物多样性减少的条件下进行的；只有少数是在开放系统或农田中进行的，其中土壤微生物的多样性较高。在这里，我们研究了微生物如何影响低剂量草甘膦诱导的毒物兴奋作用。为此，我们使用了拟南芥和一个由 185 个菌株组成的特征良好的合成细菌群落 (SynCom)，该群落模拟了拟南芥根部相关的微生物组。我们发现，3.6 × 10 ^-6 g酸当量/升（低剂量的草甘膦，或LDG）的剂量使未接种植物的芽干重（即兴奋作用）增加约14%。出乎意料的是，在接种 SynCom 的植物中，LDG 使芽干重减少了约 17%。我们发现 LDG 富集了根部的两种厚壁菌门和两种伯克霍尔德氏菌菌株。已知这些特定菌株在单缔合测定中充当根生长抑制剂 (RGI)。我们通过组装缺乏 RGI 菌株的新合成群落，测试了 RGI 与 LDG 中芽干重减少之间的联系。将 RGI 菌株从群落中剔除可恢复 LDG 的生长诱导。最后，我们表明来自一些特定门的单个 RGI 菌株足以将对 LDG 的反应从促进生长转变为抑制生长。我们的结果表明，草甘膦毒物兴奋作用完全取决于根部微生物组的组成，特别是根部生长抑制剂菌株的存在。