Beneficial rhizobacteria promote plant growth and protect plants against phytopathogens. Effective colonization on plant roots is critical for the rhizobacteria to exert beneficial activities. How bacteria migrate swiftly in the soil of semisolid or solid nature remains unclear. Here we report that sucrose, a disaccharide ubiquitously deployed by photosynthetic plants for fixed carbon transport and storage, and abundantly secreted from plant roots, promotes solid surface motility (SSM) and root colonization by Bacillus subtilis through a previously uncharacterized mechanism. Sucrose induces robust SSM by triggering a signaling cascade, first through extracellular synthesis of polymeric levan, which in turn stimulates strong production of surfactin and hyper-flagellation of the cells. B. subtilis poorly colonizes the roots of Arabidopsis thaliana mutants deficient in root-exudation of sucrose, while exogenously added sucrose selectively shapes the rhizomicrobiome associated with the tomato plant roots, promoting specifically bacilli and pseudomonad. We propose that sucrose activates a signaling cascade to trigger SSM and promote rhizosphere colonization by B. subtilis. Our findings also suggest a practicable approach to boost prevalence of beneficial Bacillus species in plant protection.

有益的根际细菌促进植物生长并保护植物免受植物病原体的侵害。植物根部的有效定殖对于根际细菌发挥有益活性至关重要。细菌如何在半固体或固体性质的土壤中迅速迁移仍不清楚。在这里，我们报告了蔗糖，一种由光合植物广泛用于固定碳运输和储存的二糖，并从植物根部大量分泌，通过以前未表征的机制促进枯草芽孢杆菌的固体表面运动 (SSM) 和根部定殖。蔗糖通过触发信号级联来诱导强大的 SSM，首先通过聚合果聚糖的细胞外合成，这反过来又刺激了表面活性素的强烈产生和细胞的过度鞭毛。枯草芽孢杆菌缺乏蔗糖根系分泌的拟南芥突变体的根部定殖较差，而外源添加的蔗糖选择性地塑造了与番茄植物根系相关的根际微生物组，特别促进了杆菌和假单胞菌的生长。我们建议蔗糖激活信号级联以触发 SSM 并促进枯草芽孢杆菌的根际定殖。我们的研究结果还提出了一种可行的方法来提高植物保护中有益芽孢杆菌的流行率。