Porphyromonas gingivalis Horizontal DNA Transfer and Genetic Variation

描述(申请人提供)：对于许多细菌来说，人类是他们唯一的栖息地，这些细菌的进化是对来自宿主环境的选择压力的反应。由于每个人类宿主代表着一个独特的生态位，因此可能需要针对特定的宿主定制有助于定植和致病的细菌毒力因子，以便最大限度地适合微生物。尽管所有的细菌都能够通过随机突变来使其基因组多样化，但在菌株之间转移DNA的物种在将有用的突变重新分类到同一细菌细胞中的能力方面具有额外的优势。牙龈卟啉单胞菌是一种革兰氏阴性厌氧菌，它定植于人的龈下缝隙中的菌斑生物膜，是慢性和严重牙周病的病原体。牙龈假单胞菌是一个遗传多样性的物种，但人们对这种多样性是如何产生的，或者它如何在慢性感染期间帮助这些重要病原体的适合性知之甚少。该项目的长期目标是了解遗传多样性如何有助于慢性牙周感染的健康。作为实现这一目标的第一步，这项应用的目标是确定牙龈假单胞菌遗传变异的分子机制，并以多物种生物膜形成为模型系统，测量DNA变化对细菌适合度的影响。这些目标是基于在牙龈假单胞菌中发现的一个基本的新行为：我们假设的菌株之间的染色体DNA转移是这些口腔病原体的主要多样性产生机制。我们将追求以下三个具体目标来解决这一假设。目的一：寻找控制牙龈假单胞菌染色体DNA水平转移的基因。目的二：确定物种内染色体DNA转移的流行率。目的三：确定在牙龈假单胞菌生物被膜形成过程中有助于健康改善的基因改变。本提案中描述的实验将确定水平DNA转移对复杂细菌表型的影响。识别在环境压力下被转移和有利选择的细菌基因将为识别牙周病的治疗靶点提供新的框架。 公共卫生相关性：牙周病是牙齿和牙床长期细菌感染的结果。某些细菌病原体，如牙龈卟啉单胞菌，能够避免宿主免疫反应，很难用手动清洁方法和抗生素治疗来清除。我们的研究目标是了解基因适应如何使牙龈卟啉单胞菌在人类口腔中持续存在。如果我们能够了解细菌正在使用什么方法来改善它们的健康状况，那么我们就可以设计出更好的治疗方法来治疗患者。

DESCRIPTION (provided by applicant): For many bacteria, humans are their only habitat, and evolution in these bacteria is in response to selective pressure from the host environment. As each human host represents a unique ecological niche, bacterial virulence factors that contribute to colonization and pathogenicity may need to be tailored to the specific host, in order to maximize fitness of the microorganism. Although all bacteria are able to diversify their genomes by random mutagenesis, species that also transfer DNA between strains have an added advantage in their ability to re-assort useful mutations into the same bacterial cell. Porphyromonas gingivalis is a Gram-negative anaerobe that colonizes plaque biofilms in the human subgingival crevice, and is a causative agent in the development of chronic and severe periodontal disease. P. gingivalis is a genetically diverse species, but little is known about how this diversity is generated, or how it contributes to the fitness of these important pathogens during chronic infections. The long-term goal of this project is to understand how genetic diversity contributes to fitness in chronic periodontal infections. As a first step towards this goal, the objective of this application is to determine the molecular mechanisms underlying genetic variability in P. gingivalis, and to measure the effect of DNA changes on bacterial fitness, using multi-species biofilm formation as a model system. These goals have been formulated based on a fundamental new behavior discovered in P. gingivalis: chromosomal DNA transfer between strains, which we hypothesize, is a major diversity generating mechanism for these oral pathogens. We will pursue the following three specific aims to address this hypothesis. Aim One: Identify the genes that control horizontal transfer of chromosomal DNA in P. gingivalis. Aim Two: Determine the prevalence of chromosomal DNA transfer within the species. Aim Three: Identify genotypic changes that contribute to fitness improvements during P. gingivalis biofilm formation. The experiments described in this proposal will determine the effect of horizontal DNA transfer on complex bacterial phenotypes. The identification of bacterial genes that are transferred and favorably selected in response to environmental pressure will provide a novel framework for the identification of therapeutic targets for treatment of periodontal disease. PUBLIC HEALTH RELEVANCE: Periodontal disease results from a long-term bacterial infection of the teeth and gums. Certain bacterial pathogens, such as Porphyromonas gingivalis, are able to avoid host immune responses, and are difficult to remove with manual cleaning methods as well as antibiotic treatments. Our research goals are to understand how genetic adaptation allows Porphyromonas gingivalis to persist in the human mouth. If we can understand what methods the bacteria are using to improve their fitness, then we can design better therapies for treating patients.