Significance of Bacteroides fragilis polysaccharide phase variation

描述（由申请人提供）：拟杆菌是人类肠道微生物群中数量占优势的属之一，它们是互利共生体，为人类提供有益的特性。在天然结肠生态位之外，脆弱拟杆菌是一种机会致病菌，是厌氧菌血症和腹内脓肿的主要原因。脆弱拟杆菌每株合成八种荚膜多糖，这有助于该生物体在其天然肠道生态位中提供共生益处，并在细菌进入肠外位点时引起疾病。我们的长期目标是了解这些荚膜多糖在肠道和肠外部位的重要性及其对这两个过程的重要性。我们在了解这些多糖复杂调控的分子机制方面取得了广泛进展；然而，我们仍然缺乏对为什么这种生物体进化到合成八种不同的荚膜多糖并改变它们的表达的基本理解。在此应用中，我们将应用我们积累的有关这些表面分子调控的大量数据来开始回答这个非常重要的生物学问题。对于目标 1，我们将确定为什么需要将细菌封装起来才能在无菌小鼠肠道中定殖。我们还将确定单独表达八种荚膜多糖中每一种的突变体在与野生型竞争肠道定植的能力方面是否相同。在目标 2 中，我们将使用体外和体内测定来开始解决为什么这些生物体进化为合成大量荚膜多糖并协调调节和相变其表达背后的生物学意义。在目标 3 中，我们将直接分析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拟杆菌的人类粪便和临床样本，以直接分析这些相关样本中的细菌。完成这些目标将极大地有助于我们了解肠道微生物群中的这些重要细菌。这些实验将使我们能够确定为什么这些生物体进化出这种有趣的生物特性及其对人类健康和疾病的贡献。 公共健康相关性：完成本提案的目标将大大增加我们对脆弱拟杆菌荚膜多糖对人类健康（共生）和疾病（腹内脓肿）贡献的认识。我们获得的有关荚膜多糖独特调节和表达谱的生物学相关性的数据越多，我们就越能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.