Genetic Basis of Abscess Formation by B. fragilis

描述(申请人提供)：脆弱类杆菌是厌氧菌血症和腹内脓肿的主要原因。原型菌株9343的衣壳多糖复合体赋予该生物体产生脓肿的特性。9343的包膜多糖复合体由至少8个不同的包膜多糖(PSA1-PSH1)组成。对于菌株9343来说，PSA1不仅对脓肿的形成至关重要，而且是该菌形成脓肿所必需的唯一多糖。脆弱芽孢杆菌染色体上含有PSA1生物合成位点的区域是异质性的，因此，不同的脆弱芽孢杆菌菌株合成的PSA分子在结构上是不同的。目前尚不清楚其他毒力菌株的PSA分子是否也赋予该微生物产生脓肿的潜力。PSA1的两性离子性质，每个重复单位既有正电荷又有负电荷，对于它的脓肿潜能是必不可少的。PSA1生物合成基因的两个基因wcfr和wcfS在所有菌株的PSA生物合成基因中都是保守的。基于同源性的数据表明，这些基因的产物参与了PSA1带正电的单糖AATGaI的形成。因此，很可能所有的脆弱芽孢杆菌菌株都合成了带有相同正电荷的单糖(AATGal)的PSA分子。基于AATGal对9343株PSA1毒力的重要性，我们的总体假设是PSA分子赋予每个毒株的脓肿潜能。这项应用分为三个目标，旨在解决这一假设，首先在物种水平上，通过突变产生结构不同的PSA分子的各种菌株的PSA基因座，并测试这些突变体诱导脓肿的能力。接下来，将对预计参与合成AATGal的基因及其产物进行生化和遗传学分析。我们现在有了工具和足够的科学基础来确定为什么脆弱杆菌物种作为一个整体具有脓肿产生能力，而不仅仅是理解原型菌株的这种现象。从这些目的获得的数据可能使我们实现我们的目标，即阐明该物种形成脓肿的遗传基础。

DESCRIPTION (provided by applicant): Bacteroides fragilis is the leading cause of anaerobic bacteremia and intraabdominal abscesses. The capsular polysaccharide complex of the prototype strain, 9343, confers the abscessogenic properties of the organism. The capsular polysaccharide complex of 9343 is comprised of at least eight distinct capsular polysaccharides (PSA1 - PSH1). For strain 9343, PSA1 is not only crucial for abscess formation, but is the only polysaccharide necessary for abscess formation by this organism. The region of the B. fragilis chromosome containing the PSA1 biosynthesis locus is heterogeneous, therefore, the PSA molecules synthesized by different B. fragilis strains are structurally distinct. It is not known whether the PSA molecules of other virulent strains also confer the abscessogenic potential of that organism. The zwitterionic nature of PSA1 of 9343, having both a positive and negative charge per repeating unit, is essential for its abscessogenic potential. Two genes of the PSA1 biosynthesis locus, wcfR and wcfS, are conserved in the PSA biosynthesis loci of all strains analyzed. Homology-based data suggest that the products of these genes are involved in the formation of the positively charged monosaccharide of PSA1, AATGaI. Therefore, it is likely that all B. fragilis strains synthesize a PSA molecule with this same positively charged monosaccharide (AATGal). Based on the importance of AATGal to the virulence of the PSA1 of 9343, our overall hypothesis is that the PSA molecule confers the abscessogenic potential of each virulent strain. This application is divided into three aims that will address this hypothesis, first at the species level by mutating the PSA loci of various strains that produce structurally distinct PSA molecules and testing these mutants for their ability to induce abscesses. Next, the genes and their products that are predicted to be involved in the synthesis of AATGal will be analyzed biochemically and genetically. We now have the tools and an adequate scientific foundation to determine why the species B. fragilis as a whole has abscessogenic capabilities rather than only understanding this phenomenon for the prototype strain. The data gained from these aims may allow us to realize our goal of elucidating the genetic basis of abscess formation by this species.