Verplaetse Emilie, Slamti Leyla, Gohar Michel, Lereclus Didier
mBio. 2015 Apr 28;6(3):e00138-15. doi: 10.1128/mBio.00138-15.
Bacillus thuringiensis (Bt) is armed to complete a full cycle in its insect host. During infection, virulence factors are expressed under the control of the quorum sensor PlcR to kill the host. After the host's death, the quorum sensor NprR controls a necrotrophic lifestyle, allowing the vegetative cells to use the insect cadaver as a bioincubator and to survive. Only a part of the Bt population sporulates in the insect cadaver, and the precise composition of the whole population and its evolution over time are unknown. Using fluorescent reporters to record gene expression at the single-cell level, we have determined the differentiation course of a Bt population and explored the lineage existing among virulent, necrotrophic, and sporulating cells. The dynamics of cell differentiation were monitored during growth in homogenized medium, biofilm formation, and colonization of insect larvae. We demonstrated that in the insect host and in planktonic culture in rich medium, the virulence, necrotrophism, and sporulation regulators are successively activated in the same cell. In contrast, in biofilms, activation of PlcR is dispensable for NprR activation and we observed a greater heterogeneity than under the other two growth conditions. We also showed that sporulating cells arise almost exclusively from necrotrophic cells. In biofilm and in the insect cadaver, we identified an as-yet-uncharacterized category of cells that do not express any of the reporters used. Overall, we showed that PlcR, NprR, and Spo0A act as interconnected integrators to allow finely tuned adaptation of the pathogen to its environment.
Bt is an entomopathogen found ubiquitously in the environment and is a widely used biopesticide. Studies performed at the population level suggest that the infection process of Bt includes three successive steps (virulence, necrotrophism, and sporulation) controlled by different regulators. This study aimed to determine how these phenotypes are activated at the cellular level and if they are switched on in all cells. We used an insect model of infection and biofilms to decipher the cellular differentiation of this bacterium under naturalistic conditions. Our study reveals the connection and lineage existing among virulent, necrotrophic, and sporulating cells. It also shows that the complex conditions encountered in biofilms and during infection generate great heterogeneity inside the population, which might reflect a bet-hedging strategy to ameliorate survival. These data generate new insights into the role of regulatory networks in the adaptation of a pathogen to its host.
苏云金芽孢杆菌（Bt）能够在其昆虫宿主内完成完整的生命周期。在感染过程中，毒力因子在群体感应传感器PlcR的控制下表达以杀死宿主。宿主死亡后，群体感应传感器NprR控制一种坏死营养型生活方式，使营养细胞能够将昆虫尸体用作生物培养箱并存活下来。只有一部分Bt群体在昆虫尸体中形成芽孢，整个群体的确切组成及其随时间的演变尚不清楚。我们使用荧光报告基因在单细胞水平记录基因表达，确定了Bt群体的分化过程，并探索了致病、坏死营养和产芽孢细胞之间存在的谱系关系。在匀浆培养基中生长、生物膜形成以及昆虫幼虫定殖过程中监测细胞分化的动态。我们证明在昆虫宿主和丰富培养基中的浮游培养中，毒力、坏死营养和芽孢形成调节因子在同一细胞中依次被激活。相比之下，在生物膜中，PlcR的激活对于NprR的激活是可有可无的，并且我们观察到比其他两种生长条件下更大的异质性。我们还表明，产芽孢细胞几乎完全来自坏死营养细胞。在生物膜和昆虫尸体中，我们鉴定出一类尚未表征的细胞，它们不表达所使用的任何报告基因。总体而言，我们表明PlcR、NprR和Spo0A作为相互连接的整合因子，使病原体能够对其环境进行精细调节以适应。
Bt是一种在环境中普遍存在的昆虫病原体，也是一种广泛使用的生物杀虫剂。在群体水平上进行的研究表明，Bt的感染过程包括由不同调节因子控制的三个连续步骤（毒力、坏死营养和芽孢形成）。本研究旨在确定这些表型在细胞水平上是如何被激活的，以及它们是否在所有细胞中都被开启。我们使用昆虫感染模型和生物膜来解读这种细菌在自然条件下的细胞分化。我们的研究揭示了致病、坏死营养和产芽孢细胞之间存在的联系和谱系关系。它还表明，生物膜和感染过程中遇到的复杂条件会在群体内部产生很大的异质性，这可能反映了一种用于提高存活率的风险对冲策略。这些数据为调节网络在病原体适应宿主中的作用提供了新的见解。
