Porphyromonas gingivalis Horizontal DNA Transfer and Genetic Variation

描述（由申请人提供）：对于许多细菌来说，人类是它们唯一的栖息地，这些细菌的进化是对宿主环境选择压力的反应。由于每个人类宿主都代表一个独特的生态位，因此可能需要为特定宿主定制有助于定植和致病性的细菌毒力因子，以最大限度地提高微生物的适应性。尽管所有细菌都能够通过随机诱变使其基因组多样化，但也在菌株之间转移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（Porphyromonas gingivalis）是一种革兰氏阴性厌氧菌，其在人类龈下缝隙中定植菌斑生物膜，并且是慢性和严重牙周病发展的病原体。牙龈卟啉单胞菌是一种遗传多样性物种，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有助于这些重要病原体的适应性知之甚少。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，本申请的目的是确定牙龈卟啉单胞菌遗传变异性的分子机制，并使用多物种生物膜形成作为模型系统来测量DNA变化对细菌适应性的影响。这些目标是基于在牙龈卟啉单胞菌中发现的一种基本的新行为制定的：我们假设菌株之间的染色体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个假设。目的一：鉴定控制牙龈卟啉单胞菌染色体DNA水平转移的基因。目的二：确定物种内染色体DNA转移的普遍性。目的三：确定牙龈卟啉单胞菌生物膜形成过程中有助于适应性改善的基因型变化。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。识别的细菌基因转移和有利的选择，以应对环境压力将提供一个新的框架，为确定治疗牙周病的治疗目标。 与公共卫生的相关性：牙周病是由牙齿和牙龈的长期细菌感染引起的。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，并且难以用手动清洁方法以及抗生素治疗去除。 我们的研究目标是了解遗传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使用什么方法来改善它们的适应性，那么我们就可以设计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.