Significance of Bacteroides fragilis polysaccharide phase variation

描述(申请人提供)：类杆菌是人类肠道微生物区系中数量占优势的属之一，它们是互惠共生的，为人类提供有益的特性。在自然结肠生态位之外，脆弱类杆菌是一种机会性病原体，是厌氧菌血症和腹内脓肿的主要原因。脆弱芽孢杆菌每个菌株合成8个胶囊多糖，这些多糖有助于这种生物在其自然的肠道生态位中提供共生益处，并在细菌进入肠外部位时导致疾病。我们的长期目标是了解这些胶囊多糖在肠道和肠外部位的重要性，以及它们对这两个过程的重要性。我们已经在了解这些多糖的复杂调控的分子机制方面取得了广泛的进展，但是，我们仍然缺乏对这种生物为什么进化到合成8种不同的被膜多糖及其表达的时相变化的基本了解。在这个应用中，我们将应用我们积累的关于这些表面分子的调控的广泛数据来开始回答这个非常重要的生物学问题。对于目标1，我们将确定为什么细菌需要被包裹起来才能在灵生菌小鼠的肠道中定植。我们还将确定单独表达八种荚膜多糖的突变体在与野生型竞争肠道定植方面是否具有同等的能力。在目标2中，我们将使用体外和体内测试来开始解决这些生物进化为合成大量胶囊多糖并协调调节它们的表达和阶段变化背后的生物学意义。在目标3中，我们将直接分析从代表共生和疾病的不同环境中分离的细菌的多糖表达谱。对于这些分析，我们将获取含有脆弱芽孢杆菌的人类粪便和临床样本，以便直接从这些相关样本中分析细菌。这些目标的完成将极大地有助于我们了解肠道微生物区系中的这些重要细菌。这些实验将使我们能够确定为什么这些生物进化出这种有趣的生物学特性，以及它对人类健康和疾病的贡献。 公共卫生相关性：完成这项提案的目标将极大地增加我们对脆弱类杆菌荚膜多糖对人类健康(共生)和疾病(腹内脓肿)的贡献的认识。我们获得的关于荚膜多糖独特调控和表达谱的生物学相关性的数据越多，我们就越能更好地了解我们与这些丰富的肠道细菌的关系。

DESCRIPTION (provided by applicant): The Bacteroides are one of the numerically dominant genera of the human intestinal microbiota where they are mutualistic symbionts providing beneficial properties to humans. Outside of the natural colonic niche, Bacteroides fragilis is an opportunistic pathogen and is the leading cause of anaerobic bacteremia and intraabdominal abscesses. B. fragilis synthesizes eight capsular polysaccharides per strain, which are instrumental in the ability of this organism to both provide symbiotic benefits in its natural intestinal niche, and to cause disease if the bacterium gains access to extraintestinal sites. Our long-term objective is to understand the importance of these capsular polysaccharides in both the intestine and extraintestinal sites and their importance to both processes. We have made extensive progress in understanding the molecular mechanisms governing the complex regulation of these polysaccharides; however, we still lack a fundamental understanding of why this organism has evolved to synthesize eight distinct capsular polysaccharides and phase vary their expression. In this application, we will apply the extensive data we have accumulated regarding regulation of these surface molecules to begin to answer this very important biological question. For Aim 1, we will determine why the bacteria need to be encapsulated in order to colonize the gnotobiotic mouse intestine. We will also determine if mutants expressing each of the eight capsular polysaccharides singly are equivalent in their ability to competitively compete with wild type for intestinal colonization. In Aim 2, we will use both in vitro and in vivo assays to begin to address the biological significance behind why these organisms have evolved to synthesize an extensive number of capsular polysaccharides and coordinately regulate and phase vary their expression. In Aim 3, we will directly analyze polysaccharide expression profiles from bacteria isolated from different environments representing both symbiosis and disease. For these analyses, we will obtain human fecal and clinical samples containing B. fragilis to analyze the bacteria directly from these relevant samples. Completion of these aims will greatly contribute to our understanding of these important bacteria of our intestinal microbiota. These experiments will allow us to determine why these organisms evolved this intriguing biological property and its contribution to human health and disease. PUBLIC HEALTH RELEVANCE: Completion of the aims of this proposal will greatly increase our knowledge of the contribution of the capsular polysaccharides of Bacteroides fragilis to human health (symbiosis) and disease (intraabdominal abscesses). The more data we obtain about the biological relevance of the unique regulation and expression profiles of the capsular polysaccharides, the better we will understand our relationship with these abundant intestinal bacteria.