The soilborne pathogen Ralstonia solanacearum causes a lethal bacterial wilt disease of tomato and many other crops by infecting host roots, then colonizing the water-transporting xylem vessels. Tomato xylem sap is nutritionally limiting but it does contain some carbon sources, including sucrose, trehalose, and myo-inositol. Transcriptomic analyses revealed that R. solanacearum expresses distinct catabolic pathways at low cell density (LCD) and high cell density (HCD). To investigate the links between bacterial catabolism, infection stage, and virulence, we measured in planta fitness of bacterial mutants lacking specific carbon catabolic pathways expressed at either LCD or HCD. We hypothesized that early in disease, during root infection, the bacterium depends on carbon sources catabolized at LCD, while HCD carbon sources are only required later in disease during stem colonization. A R. solanacearum ΔiolG mutant unable to use the LCD-catabolized nutrient myo-inositol was defective in tomato root colonization, but after it reached the stem this strain colonized and caused symptoms as well as wild type. In contrast, R. solanacearum mutants unable to use the HCD-catabolized nutrients sucrose (ΔscrA), trehalose (ΔtreA), or both (ΔscrA/treA), infected roots as well as wild-type R. solanacearum but were defective in colonization and competitive fitness in midstems and had reduced virulence. Further, xylem sap from tomato plants colonized by ΔscrA, ΔtreA, or ΔscrA/treA R. solanacearum mutants contained twice as much sucrose as sap from plants colonized by wild-type R. solanacearum. Together, these findings suggest that quorum sensing specifically adapts R. solanacearum metabolism for success in the different nutritional environments of plant roots and xylem sap.

Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

土传病原体青枯病菌通过感染宿主根部，然后定植于运输水的木质部血管，导致番茄和许多其他作物的致命青枯病。番茄木质部汁液在营养上是有限的，但它确实含有一些碳源，包括蔗糖、海藻糖和肌醇。转录组学分析表明，青枯菌在低细胞密度 (LCD) 和高细胞密度 (HCD) 下表达不同的分解代谢途径。为了研究细菌分解代谢、感染阶段和毒力之间的联系，我们测量了缺乏在 LCD 或 HCD 上表达的特定碳分解代谢途径的细菌突变体的植物适应性。我们假设在疾病早期，在根部感染期间，细菌依赖于 LCD 分解代谢的碳源，而 HCD 碳源仅在茎定植期间疾病后期才需要。甲青枯Δ iolG突变体不能使用LCD-分解代谢营养肌醇是番茄根定殖有缺陷的，但它达到后的干该菌株定植和引起的症状以及野生型。相比之下，R. solanacearum无法使用 HCD 分解代谢的营养物质蔗糖 (Δ scrA)、海藻糖 (Δ treA)或两者 ( ΔscrA/treA ) 的突变体，感染根以及野生型青枯菌，但在中间体中的定植和竞争适应性存在缺陷并降低了毒力。此外，来自被 Δ scrA、Δ treA或 Δ scrA/treA R. solanacearum突变体定殖的番茄植物的木质部汁液所含的蔗糖是野生型青枯菌定植植物的汁液的两倍。总之，这些发现表明群体感应特别适应青枯菌 在植物根部和木质部汁液的不同营养环境中成功的代谢。

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