Sinorhizobium meliloti factors that affect biofilm formation and symbiosis efficiency

项目总结/摘要 该项目将阐明控制极性粘附素生产、生物膜 形成和宿主定植在α-变形菌中，α-变形菌是一个生理上异质的群体，包括 大量的人类病原体。特别是与公共卫生相关的，生物膜形成起着至关重要的作用。 在不同环境中细菌的生存中的作用：生物膜中的细胞不情愿地附着在生物和非生物膜上。 表面，发展抗菌剂的耐药性增加，并有助于持续感染。 虽然限制生物膜的形成有可能预防和限制微生物疾病，但知之甚少 关于α-变形菌形成生物膜以及它如何促进宿主定植。 我们以前发现了一种与生物膜相关的突变，这种突变在中华根瘤菌的实验室菌株中很常见 苜蓿属，一种模式α-变形杆菌，与相容的豆类形成互惠共生， 定殖根组织并固定氮以交换来自植物宿主的营养。纠正突变 恢复了保守极性因子PodJ的全长产生，从而能够合成固着物（a 极性粘附素）和牢固生物膜的组装，以前从未观察到的表型。我们发现生物膜- 在宿主感染过程中，感受态菌株比生物膜缺陷型菌株具有竞争优势。经由 转座子诱变，我们确定了一些基因参与生物膜的发展，包括一个 编码保守转录因子（LdtR）的一种和编码二鸟苷酸环化酶的另一种，和 磷酸二酯酶，已知调节c-di-GMP第二信使的水平。本提案的目标 是（a）破译生物膜形成和宿主定殖期间的关键调控因子的职责，和（B） 建立共生与环境因子关系的监测体系。我们计划 通过实现以下三个具体目标来实现这些目标。(1)我们将确定LdtR如何 表达是受调节的，以及它执行什么样的细胞功能。(2)我们将评估调节c- di-GMP水平有助于生物膜形成和宿主感染。(3)我们将评估共生是否会影响 宿主对有毒化合物的反应以及化学胁迫和其他微生物如何影响宿主-共生体 交互.调查结果将提供一个更好的模型，说明细胞和外部因素如何 有助于α-变形菌的粘附、生物膜形成和宿主入侵。 除了实现上述科学目标外，对该提案的资助将 提高研究生产力和研究人员的补助竞争力，并允许学生，特别是 那些来自代表性不足的背景，以获得研究培训和生物医学事业的准备。

Project Summary / Abstract The proposed project will elucidate the mechanisms that control polar adhesin production, biofilm formation, and host colonization in alpha-proteobacteria, a physiologically heterogeneous group that includes a number of significant human pathogens. Particularly relevant to public health, biofilm formation plays a crucial role in the survival of bacteria in diverse environments: cells in biofilms attach recalcitrantly to biotic and abiotic surfaces, develop increased resistance to antimicrobial agents, and contribute to persistent infections. Although limiting biofilm formation has the potential to prevent and restrict microbial diseases, little is known about biofilm formation by alpha-proteobacteria and how it facilitates host colonization. We previously discovered a biofilm-associated mutation common in laboratory strains of Sinorhizobium meliloti, a model alpha-proteobacterium that forms mutualistic symbiosis with compatible legumes by colonizing root tissues and fixing nitrogen in exchange for nutrients from plant hosts. Correcting the mutation restored full-length production of the conserved polarity factor PodJ, thus enabling synthesis of the holdfast (a polar adhesin) and assembly of robust biofilms, phenotypes never observed before. We found that biofilm- competent strains possess a competitive advantage over biofilm-deficient strains during host infection. Via transposon mutagenesis, we identified a number of genes involved in biofilm development, including one encoding a conserved transcription factor (LdtR) and another encoding a diguanylate cyclase and phosphodiesterase, known to modulate levels of the c-di-GMP second messenger. The goals of this proposal are (a) to decipher the responsibilities of key regulators during biofilm formation and host colonization and (b) to establish a system for monitoring the relationship between symbiosis and environmental factors. We plan to achieve these goals by accomplishing the following three specific aims. (1) We will determine how LdtR expression is regulated and what cellular functions it performs. (2) We will assess how factors that modulate c- di-GMP levels contribute to biofilm formation and host infection. (3) We will evaluate whether symbiosis affects host response to toxic compounds and how chemical stress and other microbes influence host-symbiont interactions. Results from the investigation will provide a better model of how cellular and external factors can contribute to adhesion, biofilm formation, and host invasion in alpha-proteobacteria. In addition to accomplishing the scientific objectives described above, funding of this proposal will enhance the research productivity and grant competitiveness of the investigator and allow students, particularly those from underrepresented backgrounds, to gain research training and preparation for biomedical careers.