Erwinia amylovora is the causal agent of fire blight, an economically-important disease affecting apple and pear production worldwide. Initial contact and infection of the host by E. amylovora mainly occurs in flowers, or in young leaves at actively-growing shoot tips. Infection via shoot tips encompasses several distinct steps which include the utilization of a Type III secretion system (T3SS) to establish bacterial populations within the apoplast, infection of the parenchyma, invasion of the xylem, attachment to xylem vessels, biofilm formation, and the eventual colonization of the xylem which manifests outwardly as wilting symptoms in the plant. After E. amylovora gains entry into the xylem, initial attachment to the xylem vessels is mediated by type I fimbriae. Conversely, the small RNA (sRNA) chaperone Hfq and associated sRNA ArcZ negatively regulate attachment and promote biofilm maturation. Attachment and biofilm formation within the xylem are enhanced by the mechanical force emerging from the flow of xylem sap. The second messenger molecule cyclic-di-GMP (c-di-GMP) regulates the transition into the biofilm phase of the infection process of E. amylovora. C-di-GMP also regulates the production of critical exopolysaccharides amylovoran and cellulose, that lend to the structural stability and growth of biofilms within the xylem vessels. In this review, we provide an in-depth evaluation of the process of biofilm formation occurring within the host, as a result of E. amylovora infection. We also provide a model encompassing the different physical and signaling factors involved in biofilm initiation and maturation in E. amylovora, and highlight what needs to be done in the future.

中文翻译：

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通过在梨火疫病菌中形成生物膜来剖析木质部定植过程

Erwinia amylovora 是火疫病的病原体，火疫病是一种影响全球苹果和梨生产的重要经济疾病。梨火疫病菌对宿主的初始接触和感染主要发生在花中，或在活跃生长的枝条尖端的幼叶中。通过芽尖感染包括几个不同的步骤，其中包括利用 III 型分泌系统 (T3SS) 在质外体内建立细菌种群、薄壁组织感染、木质部入侵、附着于木质部血管、生物膜形成和最终木质部的定植，表现为植物的萎蔫症状。在梨火疫病菌进入木质部后，对木质部血管的初始附着是由 I 型菌毛介导的。反过来，小 RNA (sRNA) 分子伴侣 Hfq 和相关的 sRNA ArcZ 负向调节附着并促进生物膜成熟。木质部汁液流动产生的机械力增强了木质部内的附着和生物膜形成。第二信使分子 cycl-di-GMP (c-di-GMP) 调节梨火疫病菌感染过程向生物膜阶段的转变。C-di-GMP 还调节关键胞外多糖 amylovoran 和纤维素的产生，这有助于木质部血管内生物膜的结构稳定性和生长。在这篇综述中，我们对由于梨火疫病菌感染而在宿主内发生的生物膜形成过程进行了深入评估。