Streptomyces bacteria are ubiquitous in soils and are well known for producing secondary metabolites, including antimicrobials. Increasingly, they are being isolated from plant roots, and several studies have shown they are specifically recruited to the rhizosphere and the endosphere of the model plant Arabidopsis thaliana. Here, we test the hypothesis that Streptomyces bacteria have a beneficial effect on A. thaliana growth and could potentially be used as plant probiotics. To do this, we selectively isolated streptomycetes from surface-washed A. thaliana roots and generated high-quality genome sequences for five strains, which we named L2, M2, M3, N1, and N2. Reinfection of A. thaliana plants with L2, M2, and M3 significantly increased plant biomass individually and in combination, whereas N1 and N2 had a negative effect on plant growth, likely due to their production of polyene natural products which can bind to phytosterols and reduce plant growth. N2 exhibits broad-spectrum antimicrobial activity and makes filipin-like polyenes, including 14-hydroxyisochainin which inhibits the take-all fungus, Gaeumannomyces graminis var. tritici. N2 antifungal activity as a whole was upregulated ∼2-fold in response to indole-3-acetic acid (IAA), suggesting a possible role during competition in the rhizosphere. Furthermore, coating wheat seeds with N2 spores protected wheat seedlings against take-all disease. We conclude that at least some soil-dwelling streptomycetes confer growth-promoting benefits on A. thaliana, while others might be exploited to protect crops against disease.

中文翻译：

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链霉菌内生菌可促进宿主健康并增强植物物种的生长。

链霉菌细菌在土壤中无处不在，并且众所周知会产生包括抗微生物剂在内的次级代谢产物。它们越来越多地从植物根中分离出来，一些研究表明它们被专门募集到模型植物拟南芥的根际和内层。在这里，我们测试了链霉菌细菌对拟南芥生长具有有益作用并且有可能被用作植物益生菌的假设。为此，我们从表面洗涤过的拟南芥根中选择性分离了链霉菌，并生成了五个菌株的高质量基因组序列，我们将其命名为L2，M2，M3，N1和N2。拟南芥再感染具有L2，M2和M3的植物单独或组合显着增加了植物的生物量，而N1和N2对植物的生长有负面影响，这很可能是由于它们产生的多烯天然产物可以与植物甾醇结合并降低植物的生长。N2表现出广谱的抗菌活性，并制造出类似磷脂的多烯，包括14-羟基异链素，它抑制所有真菌真菌（Gaeumannomyces graminis var）。小麦。响应于吲哚-3-乙酸（IAA），N2的总体抗真菌活性上调了约2倍，这表明其在根际竞争中可能发挥作用。此外，用N2孢子包被小麦种子可以保护小麦幼苗免遭全盘侵染。我们得出的结论是，至少有一些居住在土壤中的链霉菌能给拟南芥带来促进生长的好处，而另一些可能被用来保护农作物免受疾病侵害。